A Comparison between Capillary and Venous Blood in

the Determination of Anaemia in Pregnancy

A Project Report submitted to the University of Nigeria, in partial fulfilment

of the requirement for the award of the Master of Science in Human

Physiology

By

DIM, Cyril Chukwudi

(PG/MSC/06/46404)

Department of Physiology

Faculty of Medical Sciences

University of Nigeria Enugu Campus

Supervisor: - Ugochukwu Bond Anyaehie, PhD

July, 2013

CERTIFICATION

We certify that the contents of this project were conceptualized and developed

after a problem identification and discussion with the supervisor. We are certain

that the candidate conducted the study conscientiously. He has also satisfactorily

completed the requirements of the course work. The work is original, and has not

been presented to any examining body.

................................................ ......................................Dr. U. B. Anyaehie Date (Project Supervisor)

............................................... .........................................Dr. E. E. Iyare Date(Head of Department)

i

DECLARATION

I hereby declare that the research work presented in this Project Report was carried

out by me after ethical approval by the Institutional Review Board of University of

Nigeria Teaching Hospital (UNTH) Enugu.

I declare no conflict of interests. Where other peoples’ works were used in this

document, they were acknowledged and cited appropriately.

…………………………..Dim, Cyril C.

ii

DEDICATION

This Project Report is dedicated to my dear mother Lady Catherine E. DIM, who

passed on to eternal glory, during the final preparation of this work.

iii

ACKNOWLEDGEMENTS

My sincere gratitude goes to the University of Nigeria for offering me the

opportunity to participate in the programme. I thank all my lecturers especially Dr.

Udeh J. F. and Prof. Igwe J. C. for their dedication to duty. I am also very grateful

to Prof. Igwe J. C. who was supervising this project before his relocation to

another University. I commend the Head of Department – Dr. Iyare E. E. and my

current supervisor Dr. Anyaehie B. U. for their commitment to the post-graduate

programme in Human Physiology in the University of Nigeria.

I acknowledge my field officers – Drs. Obiora, Ugwu, and Ebube for assisting me

during data collection despite their busy schedule.

The project would not have been possible without the support and understanding

of my wife Ngozi, and children - Chidi, Chukwuma, and Amarachi.

Finally, I give thanks and praises to God Almighty, the giver of life for sustaining

me during the M.Sc programme.

Dim CC

iv

TABLE OF CONTENTS

Contents

CERTIFICATION................................................................................................................i

DECLARATION.................................................................................................................ii

DEDICATION....................................................................................................................iii

ACKNOWLEDGEMENTS................................................................................................iv

TABLE OF CONTENTS.....................................................................................................v

LIST OF FIGURES...........................................................................................................vii

LIST OF TABLES............................................................................................................viii

ABBREVIATIONS............................................................................................................ix

ABSTRACT.........................................................................................................................x

CHAPTER ONE: INTRODUCTION..................................................................................1

1.1 Background............................................................................................................1

1.2 Study justification..................................................................................................3

1.3 Study hypothesis....................................................................................................4

1.4 Aim and objectives................................................................................................5

1.41 Aim....................................................................................................................5

1.42 Objectives..........................................................................................................5

CHAPTER TWO: LITERATURE REVIEW......................................................................6

2.1 Human blood and pregnancy.................................................................................6

2.2 Physiologic anatomy of the capillary and vein......................................................8

2.3 Anaemia and pregnancy........................................................................................9

2.4 Capillary and venous haematocrit.......................................................................10

CHAPTER THREE: PATIENTS AND METHODS.........................................................13

3.1 Study center.........................................................................................................13

3.2 Study area............................................................................................................14

3.3 Patients................................................................................................................15

v

3.4 Eligibility.............................................................................................................15

3.5 Exclusion criteria.................................................................................................15

3.6 Study design and sample selection......................................................................16

3.7 Sample size determination...................................................................................16

3.8 Ethical clearance..................................................................................................17

3.9 Data collection and analysis................................................................................17

3.10 Quality control measures.................................................................................19

3.11 Primary outcome measure................................................................................19

3.12 Secondary outcome measures..........................................................................19

CHAPTER FOUR: RESULTS..........................................................................................20

4.1 Socio-demographic characteristics......................................................................20

4.2 Capillary and venous packed cell volume...........................................................22

4.3 Anaemia in pregnancy and its variation with source of blood............................24

4.4 Arm preference for blood sample collection.......................................................27

CHAPTER FIVE: DISCUSSION AND CONCLUSION..................................................30

5.1 Discussion............................................................................................................30

5.2 Conclusion...........................................................................................................34

5.3 Recommendations...............................................................................................34

References......................................................................................................................35

APPENDIX 1: Study profoma.......................................................................................39

APPENDIX 2: Ethical clearance certificate...................................................................40

vi

LIST OF FIGURES

Figure 1: Changes in total blood volume, plasma volume, and RBC during

pregnancy

Figure 2: Structure of blood vessels

Figure 3: Scatter diagram of cPCV versus vPCV

Figure 4: Participants arm preference for blood sample collection

vii

LIST OF TABLES

Table 1: Distribution of participants’ characteristics....................................21

Table 2: Prevalence of anaemia and gestional age groups............................25

Table 3: Anaemia in pregnancy and sources of blood sample......................26

Table 4: Participants' arm preferences and reasons.......................................29

viii

ABBREVIATIONS

ANC: Antenatal clinic

Hb: Haemoglobin

Hct: Haematocrit

n.d: No date

PCV: Packed cell volume

cPCV: Capillary packed cell volume

vPCV: Venous packed cell volume

RBC: Red blood cells

UNEC: University of Nigeria Enugu Campus

UNTH: University of Nigeria Teaching Hospital

ix

ABSTRACT

Blood samples for packed cell volume (PCV) estimation are obtained from either

the veins or capillaries. However, the volume of red cells in capillary blood varies

from venous blood. The extent of this variation as well as its impact on the

diagnosis of anaemia has not been studied in pregnancy. To determine whether

capillary blood PCV differed from venous blood PCV of apparently healthy

pregnant women in Enugu, Nigeria, as well as the effect of the source of blood on

prevalence of anaemia in pregnancy. PCV was estimated using pairs of venous and

capillary blood samples collected from a cohort of 200 consecutive pregnant

women at the antenatal clinic of UNTH Enugu. Questionnaires were used to obtain

data on participant’s arm preference for blood sample collection. Data analysis was

both descriptive and inferential at 95% confidence level. The mean capillary PCV

(cPCV) of participants was 33.5 ± 3.57% while that of venous PVC (vPCV) was

34.3 ± 3.74% (P < 0.001). The difference between cPCV and vPCV pairs ranges

from -5% to +5% (mean = -0.83 ±1.54). Prevalence of anaemia was 33.5% or

28.0% using the capillary or venous blood respectively [O.R = 1.3 (CI 95%: 0.85,

1.98)]. A majority (47.5%) of participants did not express any specific arm

preference for blood sample collection. PCV from capillary blood is significantly

lower than that of venous blood among normal pregnant women in Enugu, Nigeria.

Likewise the prevalence of anaemia in pregnancy derived from cPCV is higher

than that of vPCV. Maternity units should use venous blood for PCV estimation.

x

CHAPTER ONE: INTRODUCTION

1.1 Background

Blood is a specialized fluid made up of cells suspended in plasma. It is

essentially confined within the blood vessels which vary in structure and

function, depending on the type. The capillaries connect the arterial to the

venous vascular system and are responsible for the exchange of gases and

nutrients between cells and the blood. Only 5% of the blood is in the

capillaries and in dilated state, the calibre of the capillary is just sufficient to

permit red blood cells (RBC) to squeeze through it in a single file (Ganong,

2005). Some sites such as the fingers, ear lobes, and the heels have extensive

capillary network and are often used for the collection of blood samples for

laboratory investigations, especially packed cell volume (PCV) or

haematocrits (Hct), which is one of the most widely measured

parameters in medical practice (Baskurt et al., 2006). On the

other hand, the veins have intact walls and transmit blood from the

capillaries, through the venules, to the right chamber of the heart. They are

superficial when compared to the arteries, especially in the limbs, and are

used for collection of blood specimen for haematological and other

investigations.

Anaemia is defined as having below normal values for the total volume of

red blood cells, the number of normal red blood cells, or the amount of

hemoglobin in these cells (USAID, 1997). The proportion of blood made of

1

red blood cells is referred to as the Hct or PCV. In pregnancy, anaemia

implies a PCV of less than 33% or a haemoglobin concentration of less

11gm% (WHO, 1992). Anaemia in pregnancy continues to be a major health

problem in many developing countries and is associated with increased rates

of maternal and perinatal mortality, premature delivery, low birth weight,

and other adverse outcomes (Mahomed, 2004; Nyuke and Letsky, 2000).

More than half of the pregnant women in the world have haemoglobin levels

indicative of anaemia (WHO, 1992). However, while only 15% of pregnant

women are anaemic in developed countries, the prevalence of anaemia in

developing countries is relatively high (33-75%) (Dim and Onah 2007;

Massawe et al., 1999; Nyuke and Letsky, 2000; WHO, 1992). The

commonest cause of anaemia in pregnancy worldwide is iron deficiency

(Nyuke and Letsky, 2000). The predisposing factors include

grandmultiparity, low socio-economic status, malaria infestation, late

booking, Human Immunodeficiency Virus (HIV) infection, and inadequate

child spacing amongst others (Adinma et al., 2002; Aimaku et al, 2003;

Aluka et al., 2001; Amadi et al., 2000). Pregnant women are therefore

screened for anaemia during antenatal service and placed on prophylactic

oral iron therapy. This is an important secondary preventive health strategy

aimed at early detection and treatment of anaemia in pregnancy.

It has been shown that the red cell volume of capillary blood is less accurate

when compared to that of venous blood, especially in severe anaemia

2

(USAID, 1997). In pregnancy, there is marked physiological and anatomical

changes including the disproportionate increase in blood volume and red

blood cell mass (Koos and Moore, 2003). These changes may affect the

accuracy of capillary blood PCV which may negatively influence the

diagnoses and management of anaemia in pregnancy.

1.2 Study justification

Pregnancy is a physiological condition characterized by lots of systemic

changes necessary to support the growth of the fetus. Though most

pregnancies are normal, complications often arise causing varying degrees of

maternal and perinatal morbidity and mortality. A very important

complication of pregnancy in sub-Saharan Africa is anaemia. A report from

the study area showed a high prevalence (41.9%) of anaemia among

pregnant women at booking (Dim and Onah, 2007).

Blood samples for assessment of PCV are often collected from the veins or

the capillaries and the results got are accepted without regards to the source

of the specimen. Most often, especially in emergency situations, the capillary

blood sample from finger pricks are often used for PCV estimation probably

because it is easier and faster. However, because of peculiarities of blood

and the capillary microcirculation, it has been shown that the volume of red

cells in capillary blood varies from that of the venous blood (Baskurt et al.,

2006). This disparity between capillary and venous blood PCV has been

3

reported in several studies (Daae et al., 1988; Daae et al., 1991; Yang et al.,

2001) but none of them involved pregnant women. It is not known whether

pregnancy state attenuates the disparity or worsens it. The concern is

heightened by the fact that PCV results from both capillary and venous blood

are used interchangeably in the study area Therefore, it becomes very

important to study the similarity or otherwise of capillary and venous PCV in

pregnancy. This will ensure uniformity as regards the diagnosis of anaemia

in pregnancy.

On the other hand, it is expected that patient’s arm preference should be

sought for and respected by a caregiver / phlebotomist during the collection

of blood sample for any investigations (University of Virginia (UVA) Health

System, 2011); this should be more important during antenatal care because

a majority of pregnant women are healthy. However, this consideration does

not seem to be the practice in the study area based on the investigator’s

personal observation. Therefore, in order to initiate and encourage the

practice of seeking for and respecting arm preference during blood sample

collection from pregnant women at the study center, it is important to

demonstrate that this group of women do have varying arm preferences.

1.3 Study hypothesis

There is no difference between the mean values of capillary and venous PCV

of pregnant women in Enugu, South-eastern Nigeria.

4

1.4 Aim and objectives

1.41 Aim

To determine whether capillary blood PCV differs from venous blood

PCV of healthy pregnant women in Enugu, South-eastern Nigeria.

1.42 Objectives

To compare the mean capillary PCV(cPCV) and venous PCV

(vPCV) of normal pregnant women in Enugu

To determine the prevalence of anaemia in pregnancy and its

variation with the source of blood (capillary or venous)

To determine patients arm preference as regards to the source of

blood for PCV estimation in pregnancy.

5

CHAPTER TWO: LITERATURE REVIEW

2.1 Human blood and pregnancy

The human blood is made of cellular elements – red blood cells, white blood

cells, and platelets, suspended in plasma. The normal total circulating blood

volume is about 7% of the body weight. About 60% of this volume is plasma

while 40% is RBC, but these percentages can vary considerably depending

on gender, weight, and other factors including pregnancy (Guyton and Hall,

2006). The nature of blood as a suspension with characteristic flow

properties is the basis of the uneven distribution of total red cell mass and

plasma volume in the cardiovascular system (Gaehtgens, 1984).

In pregnancy, the most striking maternal physiologic alteration is increase in

blood volume (Koos and Moore, 2003). The average increase in volume at

term is 45-50%. The magnitude of increase is affected by the woman’s size,

gravidity, parity, and number of fetuses (Koos and Moore, 2003).

The increase in red blood cell mass is about 33%, or approximately 450 ml

of erythrocytes. However, plasma volume increases earlier in pregnancy and

faster than red blood cell volume leading to a fall in Hct until the end of the

second trimester, when the increase in RBC is synchronized with the plasma

volume increase (Koos and Moore, 2003). A graphical description of the

physiological changes in blood volume and RBC during pregnancy is shown

in figure 1.

6

Figure 1: Changes in total blood volume, plasma volume, and RBC during pregnancy

Furthermore, as part of the physiologic changes in pregnancy, there are

remarkable changes in white blood cells, platelets, and clotting factors (Koos

and Moore, 2003).

7

2.2 Physiologic anatomy of the capillary and vein

Figure 2: Structure of blood vessels

Capillaries are extremely narrow blood vessels of approximately 5-20 micro-

metres in diameter. They are supplied with blood by arterioles and drained

by venules. There are extensive networks of capillaries in most of the organs

and tissues of the body with an estimated wall area of over 6300m2 in the

adult (Ganong, 2005). This distribution of capillary network at the body

extremities such as the finger-tips and ear lobes, are utilized in clinical

practice for the collection of blood specimen for various laboratory

investigation. Capillary walls, which are about 1 micrometer thick, are made

up of a single layer of endothelial cells (Fig. 2), which permits exchanges of

material between the contents of the capillary and the surrounding tissue as

opposed to simply moving the blood around the body as in the case of other

blood vessels (IvyRose, 2012).

8

On the other hand, the walls of veins consist of three layers of tissues that are

thinner and less elastic than the corresponding layers of arteries. Unlike the

capillaries, there is no exchange of materials across walls of the veins rather;

they are responsible for transport of blood from the capillaries through the

venules to the heart (IvyRose, 2012). The intima of the limb veins is folded

at intervals to form venous valves that prevent retrograde flow of blood

(Ganong, 2005).

2.3 Anaemia and pregnancy

Anaemia in pregnancy is defined by the WHO as a haemoglobin

concentration of less than 11.0 gram% or a packed cell volume of less than

33% (WHO, 1992). It is an important cause of both maternal morbidity and

mortality. More than half of the pregnant women in the world have

haemoglobin levels indicative of anaemia (WHO, 1992). However, while

only 15% of pregnant women are anaemic in developed countries (WHO,

1993), the prevalence of anaemia in developing countries is relatively high

(33-75%) (Dim and Onah 2007; Massawe et al., 1999; Nyuke and Letsky,

2000; WHO, 1992).

The commonest cause of anaemia in pregnancy worldwide is iron deficiency

(Nyuke and Letsky, 2000). The predisposing factors include

grandmultiparity, low socio-economic status, malaria infestation, late

booking, Human Immunodeficiency Virus (HIV) infection, and inadequate

child spacing amongst others (Adinma et al., 2002; Aimaku et al, 2003;

9

Aluka et al., 2001; Amadi et al., 2000). Pregnant women are therefore

screened for anaemia during antenatal service and placed on prophylactic

oral iron therapy. This is an important secondary preventive health strategy

aimed at early detection and treatment of anaemia in pregnancy.

2.4 Capillary and venous haematocrit

Blood samples for PCV estimation are often collected from the veins or the

capillaries. However, it has been shown that the volume of red cells in

capillary blood is lower than that of the venous blood by 1% to 3% (Baskurt

et al., 2006; USAID, 1997). Also, the Hct of capillary blood is regularly

about 25% lower than the whole-body Hct (Ganong, 2001). The mechanisms

involved are the uneven distribution of red blood cells (RBCs) to daughter

branches at microvascular bifurcations, often referred to as "plasma

skimming”, the axial accumulation of erythrocytes in the small blood vessels,

as well as the difference in travelling speed between cells and plasma in the

microcirculation (Fahraeus effect) (Baskurt, 2006; Carr and Wickham, 1991;

Gaehtgens, 1981). Furthermore, insufficient deformation of RBC prevents

the cells from entering a small capillary (screening effect) (Perkkio and

Keskinen, 1983). These mechanisms are for different reasons, affected by

changes in vascular smooth muscle activity; as a consequence, haematocrit

distribution is coupled to the mechanisms regulating vascular resistance

(Gaehtgens, 1984). The effect of the pregnancy state on this disparity is

however not known.

10

In a cross-sectional study of 43 healthy adults of both sexes in Norway, Daae

et al. (1988) found that the capillary Hct and haemoglobin values

significantly exceeded those of venous blood by about 3%. The mean

capillary PCV was 41.4% while that of the venous PCV was 40.2% – the

difference ranges from – 4.9% to + 7.2%. They noted that the observed

difference might not be of any practical relevance.

In another study in Norway (Daae et al., 1991), haematological parameters

between capillary and venous blood were compared using 16 hospitalized

children aged 3 months to 14 years. The capillary Hct and haemoglobin

values exceeded those of the control (venous blood) by 3% - the mean

capillary and venous PCV were 37% and 36 % respectively. Also, the

average difference of capillary and venous PCV was +2.43% (range: -4.0%

to +11.5%). The authors suggested that blood from skin puncture was mainly

arteriolar and they attributed the difference in observed PCV to the lamina

flow which is characterized by a central and rapid stream of concentrated

RBCs.

Another cross-sectional study in China, compared the variations of blood

pictures in venous, fingertip and arterial blood (Yang et al., 2001). A pair of

venous and fingertip blood samples were simultaneously collected from 24

volunteers, and another pair of venous and arterial samples from another 12

volunteers. The volunteers were healthy adults (medical students), aged 20-

22 years, with equal males and females distribution. The mean capillary

11

(finger prick) Hct of 40.5% was not significantly different from the observed

mean venous Hct of 40.1%. However, venous Hct was significantly higher

than arterial blood by about 3.1%. Contrary to the opinions expressed by

Daae et al (1991) above, Yang and co-workers felt that the study results

suggested that blood from pin prick mainly came from capillary and small

veins rather than arterioles.

Finally, though the PCV is the percentage of the volume of occupied by red

blood cells (Ganong, 2005), it is however, impossible to completely pack the

red cells together; therefore, about 3 – 4% of the plasma remains entrapped

among the cells after centrifuging of the blood, and the true haematocrit is

only about 96% of the measured haematocrit (Guyton and Hall, 2006). This

difference results in a consistent error in PCV determination which is

disregarded in clinical practice (Lewis and Kumari, 2000).

12

CHAPTER THREE: PATIENTS AND METHODS

3.1 Study center

The study was carried out at the antenatal clinic (ANC) of University of

Nigeria Teaching Hospital (UNTH), Ituku-Ozalla, Enugu, Nigeria. The

hospital is a tertiary health care institution owned by the Federal government

of Nigeria. The new permanent hospital complex at Ituku-Ozalla is located

21 kilometers from Enugu metropolis , along Enugu-Port Harcourt Express

way (Vamed Newsletter, 2007). It was recently renovated and equipped

under the Federal Government assisted VAMED Engineering equipment

Programme. Afterwards, all services including the ANC clinic, hitherto

rendered at the old site were transferred to the permanent site with effect

from 8th January 2007 when the former was officially closed. The hospital

complex covers an area of about 200 acres and the current bed capacity is

500. There are ongoing expansion and development of the hospital within

the allocated land space of 747acres (306 hectares) (Vamed Newsletter,

2007).

In the past, UNTH Enugu was the only tertiary health care facility in the

south eastern region of the country. However with the establishment of at

least one federal health center per state of the federation, the catchment area

of the hospital is restricted mainly to Enugu state with few referrals from

neighbouring states.

13

The ANC holds every weekday. It is an obstetrician–led prenatal care where

the services are rendered by obstetricians and their resident doctors.

3.2 Study area

Enugu state is one of the five states in southeast geopolitical zone of Nigeria.

It was created in 1991 from the old Anambra state. Its capital city is Enugu.

It lies within the West African rain forest region (latitudes 5 55 and 7 10

North and longitudes 6 50 and 7 55 East), through a land area of

approximately 8000 km2 (Enugu state of Nigeria, 2004). It shares borders

with Abia State to the South, Ebonyi State to the East, Benue State to the

Northeast, Kogi State to the northwest and Anambra State to the West. The

state has 17 local government areas most of which are predominantly rural

except the three within Enugu metropolis and some parts of Oji River. The

major occupations of inhabitants range from trading and civil service in the

urban area to subsistence farming and animal pasturing in the rural areas.

Economically, the incidence of poverty in the state is about 60% which

implies all the associated problems of low incomes, poor education and

health (Enugu state of Nigeria, 2004). According to the 2006 population

census, the Enugu state and Enugu Metropolis have population of 3,267,837

and 722,664 respectively with a female to male ratio of approximately

1:1(Federal Republic of Nigeria, 2006). The State has an annual population

growth rate of about 2.83% and the population is predominantly Igbos with

pockets of other tribes (Enugu state of Nigeria, 2004). Other health facilities

14

within the state include the Enugu State University Teaching Hospital

Parklane, Enugu. In addition, there are numerous mission and private

hospitals/clinics in the State, as well as seven District Hospitals at Enugu

Urban, Udi, Agbani, Awgu, Ikem, Enugu-Ezike, and Nsukka. Also, there is

at least one health center or cottage hospital in every one of the seventeen

Local Government Areas and thirty nine Development Centers in the State

(Enugu state of Nigeria, 2004).

3.3 Patients

The study participants were selected from pregnant women attending the

ANC clinic of the study center.

3.4 Eligibility

The eligibility criterion for the study was:

Apparently health women with singleton pregnancy

3.5 Exclusion criteria

The exclusion criteria were:

Pregnant women with associated medical illness such as diabetes

mellitus and HIV infection.

Pregnant women who were acutely ill or those who presented with

obstetrics complications including pre-eclampsia, antepartum

haemorrhage.

Pregnant women who were not sure of their last menstrual period

Women who were not on haematinics

15

3.6 Study design and sample selection

The study was a cross-sectional analytical study30 of consecutive consenting

normal pregnant women attending the ANC clinic of the UNTH, Enugu,

Nigeria from the 15th day of May 2012 to 25th June 2012.

Within the study period, pregnant women who visited the hospital every

weekday for antenatal care were given a group counselling about the study.

Those who expressed interest were screened for eligibility after which

individual counselling were offered and informed consent obtained. Each

selected woman served as her own control. The recruitment continued till the

targeted sample size was achieved.

3.7 Sample size determination

The sample size (n) was determined using the formula (Bahl et al., 2010):

n = (Z1 + Z2)2 × 2S2 / (µ1 - µ2)2

Where Z1 = 1.96 i.e. Z score for α error at 5% (95% confidence level)

Z2 = 1.28 i.e. Z score for estimated study power of 90%

S = Standard deviation for the outcome in the control (mean venous PCV).

μ1-μ2 = Minimum meaningful difference between means of study and

control groups .

In clinical studies, μ1-μ2 = Effect size (E), which is

= S × standardized effect size (assumed to be 0.35)

In a study among pregnant women in Enugu, Nigeria, Nneli and Egene

(2007) found a standard deviation (s) of the mean venous PCV of 1.41%

16

Therefore E = 1.41 × 0.35 = 0.49

Therefore, n = (1.96 + 1.24)2 × 2(1.41)2 / (1.41 × 0.35)2 = 171.4 ~ 172

For the study, a sample size of 200 was used.

3.8 Ethical clearance

The study was approved by the Institutional Review Board (IRB) of UNTH

Enugu. Certificate is attached.

3.9 Data collection and analysis

There was individual counselling of each woman recruited for the study,

after which her consent was obtained. The counselling centered on the need

for research in the health sector so as to improve patient care. It also

highlighted that the information requested would be treated with utmost

confidentiality and would be used strictly for research purposes. She was

also informed that the study involved finger pricks which would elicit pain.

Afterwards, information on each woman’s socio-demographic characteristic

was obtained by trained assistants (Medical interns).

The woman’s arm preference was sought for. The thumb (palmar surface of

distal phalanx) and the cubital fossa of the preferred arm were cleaned using

cotton wool soaked with 70% alcohol (USAID, 1997). Then, a quick stab-

puncture was made with a sterile lancet on the thumb of the chosen arm and

the freely flowing blood was collected into two plain standard-sized

heparinised capillary tube without squeezing the thumb, until each was 75%

full (USAID, 1997).

17

Afterwards, 0.5 ml of blood was collected from the antecubital vein of the

preferred arm with a sterile 2 ml syringe. The blood was transferred

immediately into 2 other plain heparinised capillary tubes. Each capillary

tube containing blood sample was sealed at the inferior end with an

appropriately coloured clay sealant (red for venous blood and blue for

capillary blood), and centrifuged for 5 minutes using micro-haematocrit

centrifuge. The PCV for each capillary tube was read immediately after

centrifuging, with a micro-haematocrit reader. The mean value for each

category (capillary or venous) was recorded on a data sheet designed for the

study. The result of the venous PCV for each study participant was issued to

her on the same day and those whose results indicated anaemia were

promptly referred to their attending obstetricians

Participants’ socio-demographic characteristics such as age, educational

status, marital status and parity were sought for using semi-structured

questionnaires. All data collected from the study were keyed into the

Statistical Package for Social Sciences (SPSS) computer software version

15.0 for windows. Data analyses were both descriptive and inferential

statistics at 95% confidence level. Association were compared using

Wilcoxon Signed-Ranks Test and Spearman’s Correlation Coefficient for

continuous data, cross-tabulation and Multinomial Logistic Regression for

categorical data. Results were presented using simple percentages, tables,

18

and charts as appropriate. Association between variable were shown using p-

values, odd ratios and confidence intervals.

3.10 Quality control measures

The following measures were carried out to ensure quality control for the

study.

a. There was a clear and written study guidelines consisting of eligibility /

exclusion criteria, and study protocol for PCV estimation as well as the

recording of patients data

b. The three study assistants (2 medical interns and a resident doctor) were

trained on the study guidelines by a laboratory scientist working at the

study center.

c. The efficiency of centrifugation of the centrifuge after five minutes was

certified before the commencement of the study and weekly afterwards.

d. PCV values were read and confirmed by two assistance before recording

e. Other quality control measures were as described within the data

collection section.

3.11 Primary outcome measure

The difference between the mean venous and capillary PCV of healthy

pregnant women in Enugu, South-eastern Nigeria

3.12 Secondary outcome measures

The prevalence of anaemia in pregnancy and its variation with the source of

the blood sample.

19

CHAPTER FOUR : RESULTS

4.1 Socio-demographic characteristics

Two hundred healthy pregnant women participated in the study – each

woman served as her own control. The mean age of participants was 30.1 ±

5.05 years (range = 19 – 45). Their modal age group was 31 – 35 years

(38.0%). Only 2 participants were single while the others (99.0%) were

married. Ten (5.0%) women had primary education, 42 (21.0%) secondary

education, while 148 (74%) women had tertiary education. All participants

were Christians of varying denominations. The median parity was 1, with a

mean of 1.3 ± 1.51 (range = 0 – 6). Eighty eight women (44.0%) were

nullipara, 44 (22.0%) primipara, 60 (30.0%) multipara, and 8 (4.0%) were

grandmultipara. A majority (59.0%) of the woman had gestational ages of 28

weeks or more. Further details of participants’ characteristics are shown in

tables 1.

20

Table 1: Distribution of participants’ characteristics

Maternal characteristic

(n = 200)Sub-category Frequency (%)

Age groups (years)

16 – 20 5 (2.5)

21 – 25 33 (16.5)

26 – 30 65 (32.5)

31 – 35 76 (38.0)

36 – 40 12 (6.0)

41 – 45 9 (4.5)

Christian denomination

Roman catholic 79 (39.5)

Anglican 39 (19.5)

Methodist 8 (4.0)

Pentecostal 73 (36.5)

Jehovah witness 1 (0.5)

Tribe

Igbo 191 (95.5)

Yoruba 2 (1.0)

Hausa 0 (0.0)

Others 7 (3.5)

Gestational age groups

(weeks)

< 28 82 (41.0)

≥ 28 118 (59.0)

Body weight groups (kg)< 90 27 (13.5)

≥ 90 173 (86.5)

21

4.2 Capillary and venous packed cell volume

The mean value for the capillary PCV (cPCV) of participants was 33.5 ±

3.57% while that of venous PVC (vPCV) was 34. 3 ± 3.74%. This translated

to a 2.3% reduction of the capillary PVC from the control (venous) value.

The ranges of the cPCV and vPCV were 20 – 44 % and 21 – 44 %

respectively. Out of the 200 PCV pairs, cPCV were higher than vPCV in 18

(9.0%) women, equal in 68 (34.0%) women, but less than vPCV in 114

(57%) women. As shown in figure 3, the cPCV values of participants had

strong positive correlation with their venous values (r = 0.883, P < 0.001).

The difference between cPCV and vPCV pairs ranges from -5% to +5%, and

the mean was -0.83 ±1.54. The observed difference between the cPCV and

vPVC values of participants was statistically significant (P < 0.001).

22

23

25 30 35 40

Venous PCV (%)

20

25

30

35

40

Cap

illar

y PC

V (%

)

Figure 3: Scatter diagram of cPCV versus vPCV

4.3 Anaemia in pregnancy and its variation with source of blood

Sixty seven (33.5%) and 56 (28.0%) women were anaemic (PCV < 33%)

using the capillary or venous blood respectively. This difference of 5.5%

translated to a 19.6% increase in the prevalence of anaemia in pregnancy

derived from cPCV values when compared with that of vPCV. However, this

observed difference in the prevalence of anaemia between the two sources of

blood was not statistically significant [O.R = 1.3 (CI 95%: 0.85, 1.98) P =

0.233] – details in table 2. When controlled for the effect of lower

gestational age (<28 weeks), the odds of identifying anaemia in pregnancy

using capillary blood remained unchanged when compared to venous blood

[O.R = 1.3 (CI 95%: 0.85, 1.99) P = 0.231]

To further study the effect of lower gestational age (GA) on the prevalence

of anaemia, participants were stratified into two gestational age categories

using 28 weeks as cut off. Results of sub-analysis within these GA

categories are shown in tables 2 and 3. Thus, for women at GA of less than

28 weeks, the prevalence of anaemia increased by 6.7% for cPCV, and 4.9%

for vPCV). On the other hand, for women at GA of 28 weeks or greater, the

prevalence of anaemia reduced by 4.7% for cPCV and 3.4 for vPCV (table

3). However, within each GA category, the prevalence of anaemia had no

association with the source of the blood (P > 0.05) (table 3).

24

Table 2: Prevalence of anaemia and gestional age groups

GA category (weeks)

Source of blood

Anaemia in pregnancy P value O.R (CI: 95%)

Yes (%) No (%)

All GA

Capillary 67 (33.5) 133 (66.5) 0.233 1.3 (0.85, 1.98)

Venous 56 (28.0) 144 (72.0) -

< 28 Capillary 33 (40.2) 49 (59.8) 0.331 1.4 (0.73, 2.60)

Venous 27 (32.9) 55 (67.1) -

>= 28 Capillary 34 (28.8) 84 (71.2) 0.462 1.2 (0.70, 2.22)

Venous 29 (24.6) 89 (75.4) -

25

Source of

blood

Prevalence of anaemia (%) Difference in

prevalence

(%)

Mean

difference

(%)All GA < 28 weeks

Capillary 33.5 40.2 +6.75.8

Venous 28.0 32.9 +4.9

All GA ≥ 28 weeks

Capillary 33.5 28.8 -4.7-4.1

Venous 28.0 24.6 -3.4

Table 3: Anaemia in pregnancy and sources of blood sample

26

4.4 Arm preference for blood sample collection

In response to the structured question thus: which of your arms do you prefer

for blood collection? A majority (47.5%) of participants did not express any

specific arm preference (i.e. tolerated either arm equally), while 69 (34.5%)

women preferred the left arm. Details of the distribution of participants’ arm

preference are shown in figure 4.

Out of the 105 participants who preferred either the right or left arm, a

majority (61.9%) had no reason, 29 (27.6%) did not want the pain following

the sample collection to affect the use of their dominant arms, and the

remaining 11 (10.5%) women felt that access to blood vessels was easier on

their preferred arm. Details of the participants’ responses in relation to their

arm preferences are shown in table 4.

27

36; 18%

69; 35%

95; 48% Right armLeft armEither arm

Figure 4: Participants arm preference for blood sample collection

28

Table 4: Participants' arm preferences and reasons

ReasonArm preference

Total (%)Right arm (%) Left arm (%)

No reason 26 (40.0) 39 (60.0) 65 (100.0)

Avoid effect of after pains 6 (20.7) 23 (79.3) 29 (100.0)

Easy blood vessel access 4 (36.4) 7 (63.6) 11 (100.0)

Total 36 (34.3) 69 (65.7) 105 (100.0)

29

CHAPTER FIVE: DISCUSSION AND CONCLUSION

5.1 Discussion

This study showed that over 40% of pregnant women in the study area

belong to the 26 – 35 year age group which is not surprising since the

average age at first pregnancy at the study center is 26.2 years (Nwagha et

al., 2008). Also, the distribution of marital status of participants was

consistent with previous report (Onah et al, 2009). Furthermore, a high

proportion of study participants had tertiary education which may suggest

that women with higher education seek antenatal care at the study center;

this finding has also been observed in earlier studies (Onah et al, 2009; Dim

et al, 2011). This assumption may be correct because higher education is

expected to drive quality health seeking behaviour.

This study found that the cPCV was significantly lower than vPCV by about

1% which conforms to the report that red cell volume in capillary blood is

1% – 3% lower than venous blood (USAID, 1997). It is however, not

consistent with studies among non-pregnant adults in Norway and China

which reported higher cPCV when compared to vPCV (Daae et al., 1998;

Yang et al., 2001). The small sample sizes used by both studies were likely

to have affected their precision and validity. Unfortunately, an extensive

literature search did not identify any related studies among pregnant women

with which to compare the results of this study. The reasons for the reduced

capillary red cell volume in this study were likely due to the inherent

30

mechanisms within the human microvasculature which impacts on the

dynamics of blood flow – one of the implicated mechanisms is the

“screening effect” which implies the prevention of RBC entry into the small

capillary due to insufficient deformation (Perkkio and Keskinen, 1983).

Other mechanisms include the uneven distribution of RBCs to daughter

branches at microvascular bifurcations (plasma skimming), the axial

accumulation of erythrocytes in the small blood vessels, and the difference in

travelling speed between cells and plasma in the microcirculation (Fahraeus

effect) (Baskurt et al., 2006; Carr and Wickham, 1991; Gaehtgens, 1981).

These mechanisms are affected by vascular smooth muscle activity

(Gaehtgens, 1984). Therefore, since normal pregnancy is associated with

reduction in vascular resistance, it is likely that the magnitude of the cPCV

and vPCV disparity observed in this study will differ from that of non-

pregnant population. There is need for further studies in that area.

In this study, the maximum variability between capillary and venous PCV

pairs was 5%. This magnitude of variability can impact on patients’

management especially as regards the decision to transfuse blood or blood

products. It is therefore suggested that clinical units should define the blood

source that should be used for their patients’ management so as to ensure

consistent and reproducible results. Where such guideline does not exist,

serial PCV monitoring in patients such as during antenatal care, should

employ a consistent blood source for the same reason.

31

Furthermore, the study showed a disparity between the prevalence of

anaemia recorded by the cPCV and vPCV. Though the observed difference

was not statistically significant, it was appreciable. In view of this possible

magnitude of variability, comparison of results of studies on anaemia in

pregnancy should pay attention to the sources of blood samples. It is

interesting to note that the prevalence of anaemia (all sources) increased

among women at GA of less than 28 weeks but reduced among those in 3rd

trimester (≥ 28 weeks). This observation may be due to the effect of

physiological anaemia of pregnancy which is known to be pronounced in 2nd

trimester (Koos and Moore, 2003).

Also, with respect to the prevalence of anemia in pregnancy, the difference

between the values got from cPCV and vpCV was appreciably higher for

women less than 28 weeks of GA when compared with women in 3 rd

trimester. The reason for this obvious disparity is not clear but, it may still be

related to the varying peripheral vascular resistance which falls in early

pregnancy but increases slowly in 3rd trimester until term (Silverside and

Colman, n.d.).

For varying reasons, over half of the study participants preferred one of

either left or right arm for blood sample collection. This is interesting

because it has been observed that most health providers and phlebotomist in

our environment decide on the patient’s arm to be used for blood sample

collection without recourse to the patient’s arm preference. This study

32

findings calls for more patients respect, and exposes the need for training

and retraining of health staff in act of blood sample collection.

The study was limited by its base in one hospital which might affect its

generalization to all pregnant women in Enugu, Nigeria. Also, the

participants’ educational status which was majorly tertiary education might

suggest an inherent selection bias. If higher education is assumed to be

associated with improved nutrition then, it is likely that the average PCV (all

sources) found in this study may be higher than that of the general

population of pregnant women in the study area. However, this might not be

the case in this study because all participants were on haematinics.

Furthermore, the rigorous quality control measures observed during the

study ensured its internal validity. On the other hand, the strength of the

study lies in the fact that it is the first reported effort in Nigeria to

demonstrate the disparity between capillary and venous PCV, irrespective of

the study population. It also highlights the need for care givers to be

conscious of the source of blood used in the determination of PCV for

pregnant women.

33

5.2 Conclusion

This study has found that PCV from capillary blood is significantly lower

than that of venous blood. It also noted that the prevalence of anaemia in

pregnancy derived from cPCV is higher than that of vPCV by 5.5%.

Therefore, maternity units should use venous blood for PCV estimation or at

the least be consistent with any chosen source of blood for PCV estimation.

5.3 Recommendations

- Considering the obvious disparity between the values of cPCV and

vPCV in pregnancy, maternity units should encourage their laboratories

to use venous blood for PCV estimation. In situations where capillary

blood is used, it should be specified to guide the care giver.

- In centers where either cPCV or vPCV is used interchangeably, a source

of blood should be used consistently per patient during serial monitoring

to ensure comparability of results. Also, in cases where moderate to

severe anaemia is suspected clinically, vPCV should be used as a matter

of policy because it gives more accurate result (USAID, 1997).

- It is important that phlebotomist and caregivers enquire about, and

respect the arm preference of pregnant women during blood sample

collection for any investigation.

34

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38

APPENDIX 1: Study profoma

Serial number ______

1. Age in years (as at last birthday) __________

2. Marital status □1Single □2Married □3Widowed □4divorced

3. Religion __________________/ Denomination_____________________

4. Tribe ________________

5. What is your highest level of education _______________________

6. Which number of pregnancy is the current one (gestation) __________________

7. How many time have you delivered - dead or alive (parity) ________________

8. What your LMP ___________ Gestational age (weeks) __________

9. Which of your arms do you prefer for blood collection?

□1Right □2Left □3either

why? __________________________________________

Height (meters) ________ Weight (Kg) _______ BMI (Kg/m2) _________

Capillary PVC (%) 1 ___________ 2 ___________ Average __________

Venous PCV (%) 1 _____________ 2 ____________Average __________

39

APPENDIX 2: Ethical clearance certificate

40