Sampling

Contents:

• Specimens used for analysis

• Factors affecting the results of blood samples

• Precautions for collecting blood specimens

• Collection of Urine Specimens

SamplingSpecimens used for analysis include:

1 .Blood.

2 .Urine.

3 .CSF.

4 .Fluids obtained by tapping Pleural

Peritoneal

Pericardial

Synovial

5. Amniotic Fluid.

6. Gut Secretions : Gastric

Intestinal 7. Sweat.

8. Saliva.

9. Calculi : Renal

10. Feces. Biliary

11. Bile.

Specimens obtained must be:

• Properly labeled for identification.

• Of good quality e.g. No hemolysis in blood.

• Suitably preserved anticoagulant

refrigeration

others e.g. ice bath

Factors affecting the results of blood samples:

The most important points to bear in mind

while collecting blood samples are :

• Relation to diet

• Relation to drugs

• Relation to day time

Carbohydrate meal Bl. Glucose

Diet Protein meal Urea

Fat meal marked TG

little Cholesterol

Drugs

Oral contraceptives containing estrogens

Cortisol

T3, T4

HDL-Cholest.

TG

Therapeutic Drug Monitoring

Few to several hours after last dose.

Just before next dose

Glucose Tolerance

Diurnal variations : Cortisol am. pm.

Precautions for collecting blood specimens:1. Blood is an infectious agent.

2. Condition of the patient :

Completely relaxed

Physically (no exertion)

Mentally (allay apprehension)

30 min before

collection

Specially important for

Cortisol

Blood gases

Lactate

3. Posture of the patient:

Lying down for 20 min,

recommended for :

Plasma proteins & substances bound to them

( Ca, T3 &T4, Cortisol, Lipids)

by standing up

(redistribution

of body fluids)

by standing up

(Renin)

Aldosterone

4 .Choice of vein:

• Choose a wide vein even if palpable but not visible.

• Never collect blood from a vein in which an IV infusion is being given, even if distal to the infusion site.

5 .Cleansing of skin: Ethanol ( Not to be used if ethanol in blood is

70 % to be determined )

Isopropanol

6 .Venous Stasis:

Should be minimal

specially for:

Plasma proteins

Lactate

Coagulation Studies

Ca, Cortisol, T3&T4 , Lipids

7 .Avoid Hemolysis:

• Alcohol used for cleansing, should dry before

needle introduction.• Choice of wide vein.• Minimal venous stasis.• Clean introduction of needle into vein.• Moderate drainage of blood.• If you are using syringe for drainage, remove

the needle before delivery of blood into the tube.• Gentle mixing with the anticoagulant.

Effects of Hemolysis:

• Electrolytes : K & Mg

• Proteins E/P : -globulin

• Enzymes : LDH other enzymes e.g. AST

• May interfere with some tests

8 .Care of sample after collection: -Blood gases

-Lactate

-Pyruvate

Rapidly process the blood sample OR keep in ice bath until analysis

- Generally , separate plasma or serum as soon as possible, if not, the following changes may be observed:

a) Glucose lactate, except if collected on fluoride

b) Some substances may leak from RBCs K, LDH & P

c) Loss of CO2 & giving of O2

d) Certain enzymes are labile e.g. Acid phosphatase

Collection of Urine Specimens:• Many measurements may be done on a random

sample.

• A better value is obtained if measurement is done on a timed collection of urine e.g. 24-h sample:

1. Start at 8.00 h by completely emptying the bladder, this urine is discarded.

2. Thereafter, collect all urine voided into a container which is kept in the refrigerator. An alternative is to add a suitable preservative to the container and to mix it well with the urine each time the urine is added.

3. At 8.00 h next day urine is voided and added to the urine collected.