Submitted to Transfusion

Oavis - 1

Evaluation of blood filters for the exclusion of leukocytes from red cell

transfusions

Davis RE, Donegan EA, Vyas GN

Department of Laboratory Medicine

University of California

San Francisco, CA 94143-0100

Address correspondence and request for reprints to:

Girish N. Vyas, Ph.D.

Box 0100, Department of Laboratory Medicine

Universi ty of Cal i fornia

San Francisco, CA 94143

(415) 476-4678

Running head: Evaluation of leukocyte filters

/&$PW8\

rDavis - 2

Abstract

Filtration is a useful method for the exclusion of leukocytes from red

c e l l t r a n s f u s i o n s , p r i m a r i l y f o r t h e p r e v e n t i o n o f f e b r i l e n o n h e m o l y t i c

reactions. We experimentally evaluated five commercially-available leukocyte

fi l t e r s w i t h r e s p e c t t o r e d c e l l r e c o v e r y a n d l e u k o c y t e e x c l u s i o n i n

fi l t ra t ion of packed red eel Is . The resul ts of publ ished evaluat ions and

cl in ica l s tudies of these fi l ters, inc luding the indiv idual character is t ics of

the fi l te rs , a re p resen ted as they re la te to the i r c l in i ca l use . We have

determined that among the avai lable blood filters the Sepacel l fil ter offers

the best combinat ion of leukocyte exclusion, red cel l recovery and cost-

effect iveness in a c l in ical set t ing.

j j j i p * ^ . ,

d /h

/ P * N

Davis - 3

Introduct ion

Leukocytes in donated blood are unwanted in transfusion therapy and

f requent ly cause a l lo immuniza t ion tha t i s e t io log ic o f febr i le reac t ions1-

Since leukocytes harbor la tent and pers is tent v i ra l in fect ions, i t may be

desirable to exclude them from donated blood. Filtration of blood to exclude

the t rans fus ion o f leukocy tes in red ce l l therapy has recent ly a t t rac ted

considerable interest and has been extensively reviewed^. As compared to

other means of leukocyte removal, i t offers numerous potential advantages

including lower cost, lack of sophist icated equipment, and in some cases

longer storage life or greater leukocyte removal. We report the experimental

evaluation of five FDA-approved filters for the exclusion of leukocytes from

red cel l t ransfusions.

— ; i f e j & U - ^ r ^ ^ i ^ ^ M i w , , . — = ^

Davis - 4

f ^ M a t e r i a l s a n d m e t h o d s

F i l t e r s w e r e p r o v i d e d b y t h e r e s p e c t i v e m a n u f a c t u r e r s , a n d t h e i r

characteristics are shown in Table 1. All units tested were packed red cell

masses s to red i n Adso l (Fenwa l Labora to r i es , Deerfie ld , I L ) o r CPDA-1

(citrate-phosphate-dextrose-adenine) preservative solutions. These units were

col lected f rom volunteer donors and in tended for c l in ica l t ransfus ion, but

were excluded on the basis of an elevated serum alanine aminotransferase (>40

IU/mL) or an ant ibody to the hepat i t is B core ant igen, or both. Al l uni ts

were maintained at 4 °C. unti l the start of f i l trat ion. The age of the units

at testing, as defined by the days elapsed between collection and filtration,

is shown in Table 2. Red cell and leukocyte counts were determined before and

af te r fi l t ra t ion us ing samples drawn f rom the donor bag or the rec ip ien t

{ t ransfer bag, and were run in dupl icate on a Coul ter S automated cel l counter

(Coul ter E lect ron ics, Hia leah, FL) . For those fi l ters which depend on the

f o r m a t i o n o f m i c r o a g g r e g a t e s p r i o r t o fi l t r a t i o n ( F e n w a l a n d P a l l ) , a

modificat ion of the spin and cool method of Parrav ic in i e t a l^ was used.

Af ter obta in ing samples for prefi l t ra t ion counts , un i ts were cent r i fuged at

5000g for 20 minutes in the upright position in a swinging-bucket rotor, using

a Beckmann J-6M/E centrifuge (Beckmann Instruments, Palo Alto, CA), carefully

t ransferred to a refr igerator so as not to d isturb the buffy coat , and lef t

undisturbed at 4 °C. for at least 4 hours. For those f i l ters which require

"pr iming" to remove ai r, pyrogens, and/or ac ids f rom the fi l t rat ion column

(Imugard and Erypur), at least 400 mL of 0.9% saline solution was filtered and

discarded. All units were filtered and collected in a manner to simulate

j$fSf!\

Davis - 5

actual clinical transfusion, i.e. suspended 50-150 cm above the collection ba<

and allowed to filter at a rate of 4 mL/min, except for those filters intendec

for blood bank use prior to actual transfusion (Imugard and Erypur). Initial

inst i l lat ion of sal ine into the donor bag, wett ing of the fil ter, and use o1

t rans fus ion se ts were in accordance w i th the respec t i ve manufac tu re r ' s

d i rect ions and standard t ransfus ion pract ice. Al l but the Pal l fi l ters were

flushed wi th sa l ine a f ter fi l t ra t ion o f the un i t unt i l c lear, to improve rec

cel l recovery. When mul t ip le uni ts were successive ly fi l tered through the

same filter, similar flushing unti l clear was used between units, except for

t h e P a l l fi l t e r . H e m o l y s i s d u e t o fi l t r a t i o n w a s e x c l u d e d b y v i s u a l

inspect ion of the plasma in at least one unit f rom al l fi l ters. Volumes of

blood were calculated based on their weights and a specific gravity of 1.135.

msmmmm

J^-

Davis - 5

actual clinical transfusion, i.e. suspended 50-150 cm above the collection bag

and allowed to filter at a rate of 4 mL/min, except for those filters intended

for blood bank use prior to actual transfusion (Imugard and Erypur). Initial

inst i l la t ion of sal ine into the donor bag, wett ing of the fi l ter, and use of

t rans fus ion se ts were i n acco rdance w i th the respec t i ve manu fac tu re r ' s

d i rect ions and s tandard t ransfus ion pract ice. A l l but the Pal l fi l ters were

flushed wi th sa l ine a f ter fi l t ra t ion o f the un i t unt i l c lear, to improve red

ce l l recovery. When mul t ip le un i ts were success ive ly fi l tered through the

same filter, similar flushing unti l clear was used between units, except for

t h e P a l l fi l t e r . H e m o l y s i s d u e t o fi l t r a t i o n w a s e x c l u d e d b y v i s u a l

inspect ion of the plasma in at least one uni t f rom al l fi l ters. Volumes of

blood were calculated based on their weights and a specific gravity of 1.135.

\

Jfa.

Davis - 6

Results

A comparative summary of published results and our results is shown in

Table 2. Leukocyte removal is shown both by the percentage of or ig inal

leukocytes removed, and by the more relevant statistic of the absolute number

r e m a i n i n g a f t e r fi l t r a t i o n . R e d c e l l r e c o v e r y i s d e fi n e d s i m p l y b y t h e

percentage o f the o r ig ina l number. "Second" un i ts re fe rs to those un i ts

filtered after one unit had already been passed through the same filter. In

fi l t ra t ion o f s ing le un i t s , the re was no s ign ifican t d i f fe rence in red ce l l

r e c o v e r y b e t w e e n t h e v a r i o u s fi l t e r s ( S t u d e n t ' s t , p > . 0 5 ) . I n l e u k o c y t e

exc lus ion , the Pa l l fi l te r was s ign ificant ly less e f fec t ive than the Erypur

and Sepacel l fi l ters (p<.01), based on the absolute number of leukocytes

remaining. The Pal l fi l ter was not s ignificant ly d i fferent f rom the Imugard

filter on the basis of the absolute number of leukocytes remaining, but was

significantly different on the basis of the percentage excluded (p<.05). On

t h e b a s i s o f a b s o l u t e l e u k o c y t e s r e m a i n i n g , t h e r e w a s n o s i g n i fi c a n t

difference between the Sepacell and Erypur filters, or the Erypur and Imugard

filters; there was a significant difference between the Sepacell and Imugard

fi l te rs (p< .05) . The Fenwa l fi l te r was no t s ign ifican t l y d i f fe ren t f rom the

other filters in either red cel l recovery or leukocyte exclusion, despite the

apparently large difference in the sample means; this was probably due to the

s m a l l n u m b e r o f u n i t s fi l t e r e d w i t h t h i s fi l t e r. I n c o m p a r i n g t h e m e a n

performance of fiI ters in single vs. second units, there was no significant

difference in red cel l recovery for either the Pal l or Fenwal fil ters. Based

on the absolute number of leukocytes removed, the Fenwal filter performed

s ign i fican t l y wo rse on the second un i t s (p< .05 ) , whe reas the re was no

s ign i fican t d i f f e rence fo r t he Pa l l fi l t e r.

r

Davis - 7

Discussion

The greatest interest in removing leukocytes from red cell transfusions

has been in preventing febrile nonhemolytic reactions. The likelihood of such

a reac t ion has been cor re la ted w i th the abso lu te number o f l eukocy tes

transfused. However, there is considerable variat ion between patients (and

perhaps donors) in the minimum number of leukocytes necessary to produce a

reaction, ranging from 0.25 x 10^ to 2.5 x 109 14. Furthermore, the number of

leukocytes may be insufficient to produce a detectable reaction in a patient,

but suffic ient to cause or enhance a l lo immunizat ion. Therefore, i t seems

desirable, when practical, to reduce the number of transfused leukocytes to

t h e l o w e s t p o s s i b l e l e v e l . F u r t h e r i n c e n t i v e f o r r e d u c i n g l e u k o c y t e

transfusion exists in the possibi l i ty that leukocytes are a major vector in

the transmission of viruses: CMV15, HBV15, non-A non-B hepatitis17, EBV, and

HIV. The po ten t ia l ex is ts fo r remova l o f leukocy tes , and thus any v i ra l

agents contained therein, by filtration incorporated into the donor collection

system18; th is would have cer ta in pract ica l advantages, and prevent the

problem of viral release due to any leukocyte lysis during storage. Removal

of platelets may also be desirable, as these are usual ly nonfunctional in

packed red cell products but may cause alloimmunization. The filters l isted

here are reported to achieve varying degrees of platelet removal (Table 2).

T h e s p i n - c o o l - fi 1 t e r m e t h o d t o r e m o v e l e u k o c y t e s c o n t a i n e d a s

microaggregates can produce what might be termed a leukocyte-poor red eel 1

unit, with a total number of 0.25 to 0.5 x 109 leukocytes. Studies using this

method in chronically transfused patients have shown a dramatic reduction in

the i nc idence o f f eb r i l e nonhemo ly t i c reac t i ons ; howeve r, t he e f fec t on

alloimmunization is uncertain4*5*19*20. The adsorption column filters (Erypur

Davis - 8

and Imugard) can produce what has been termed a leukocyte-free red cell unit,

with a total number of less than 0.1 x 109 leukocytes. In several of the

units we filtered with these, the concentrat ion of leukocytes after fil trat ion

was a t o r be low the l im i t o f re l iab le de tec t ion w i th the au tomated ce l l

counter (100/microliter), so that the total number of leukocytes may even have

been less than the number calculated. Our results show that the Sepacel 1

fi l ter is a lso capable o f de l iver ing a re la t ive ly leukocyte- f ree product ; in

fact, i t had the greatest absolute leukocyte exclusion of the filters tested.

Stud ies us ing adsorpt ion co lumn fi l ters have shown v i r tua l e l iminat ion o f

febrile non-hemolytic reactions, as well as prevention and even regression of

a l lo immun iza t ion , as ev idenced by the d isappearance o f an t i - l ymphocy te

antibodies6,7,9, l l# Limited studies of the Sepacel l fil ter have also reported

no febri le reactions12*13.

I f fi l t r a t i o n i s c h o s e n b y a b l o o d b a n k a n d / o r h o s p i t a l t o r e d u c e

leukocyte transfusion, a number of factors should be considered in selecting

the type and model of fi l ter. These include: cost of the fil ter, as wel l as

additional equipment and solutions; open vs. closed systems, i.e. whether the

storage life is shortened by processing; demands on blood bank personnel;

s p e e d o f fi l t r a t i o n a n d t h e c a p a c i t y f o r m u l t i p l e u n i t s , i f u s e d u r i n g

su rge ry o r rap id t rans fus ion i s des i red ; e f fic iency o f red ce l l r ecove ry ;

platelet exclusion; and whether a leukocyte-poor, as opposed to a leukocyte-

free, product is needed. Microaggregate fil ters have the advantages of low

cost per filter and unchanged storage life; however, they require the use of a

centrifuge and blood bank personnel in spinning and cooling, and leukocyte

Davis

( ^ r e m o v a l i s o n l y s u f fi c i e n t f o r a l e u k o c y t e - p o o r p r o d u c t . I n a d d i t i o n ,formation of microaggregates (and thus leukocyte removal) increases with the

age of the unit18; depending on the degree of leukocyte exclusion desired, the

age be fo re wh i ch t he un i t canno t be fi l t e red may l eave on l y a l im i t ed

remain ing s torage l i fe , desp i te the sys tem be ing c losed. The adsorp t ion

column fil ters provide excel lent red cel l recovery and leukocyte exclusion,

a n d t h u s c a n p r o v i d e a l e u k o c y t e - f r e e p r o d u c t ; t h e y d o n o t r e q u i r e a

centrifuge or advanced preparation of the unit. However, the cost per filter

is higher, solutions are required, the storage life is limited, and blood bank

personnel time is required.

The new Sepacel l fi l ter appears to have the most advantages of the

f i 1 ters we tested. There is no decrease in storage 1 ife, del ay due to unit

- ^ p repa ra t i on , o r ex t ra wo rk f o r b l ood bank pe rsonne l . I t has been repo r ted

tha t the Sepace l l fi l te r permi ts rap id fi l t ra t ion13* ; in fi l t ra t ion - o f s ing le

un i t s , i t was t he f as tes t o f t he fi l t e r s m t es ted I n fi l t r a t i on o f second

units, the results were comparable to those of the single units, but some

fil tered too s lowly to be pract ical ; therefore, mul t ip le-uni t capaci ty cannot

be claimed for the Sepacel 1 fi1ter. A leukocyte-free product is produced,

w h i c h i s a l s o s u b s t a n t i a l l y d e p l e t e d o f p l a t e l e t s . T h e o n l y s i g n i fi c a n t

disadvantage is a greater cost per filter than for the microaggregate filters,

which may be offset by other savings.

Davis - 10

Acknowledgements

The authors wish to thank the respective manufacturers, for providing the

fi l te rs fo r tes t ing ; the I rw in Memor ia l B lood Bank in San Franc isco , fo r

providing packed red cell units; and Dr. Herbert Perkins for his crit ique of

the manuscript.

10

Davis - 11References

1) Toy PTCY, Vyas GN. Blood transfusion reactions. In: Engelfriet CP, van

Loghem JJ, von dem Borne AEGKr, eds. Immunohaematology. Amsterdam: Elsevier

Science Publishers BV, 1984:119-135. (Turk JL, ed. Research Monographs in

Immunology; vol. 5)

2) Meryman HT, Hornblower M. The preparat ion of red ce l ls depleted of

leukocytes: review and evaluation. Transfusion 1986;26:101-106

3) Mijovic V, Brozovic B, Hughes ASB, Davies TD. Leukocyte-depleted blood: A

comparison of filtration techniques. Transfusion 1983;23:30-32

4) Parravicini A, Rebul la P, Apuzzo J, Wenz B, Sirchia G. The preparation of

leukocyte-poor red cells for transfusion by a simple cost-effective technique.

Transfusion 1984;24:508-509

5 ) We n z B . M i c r o a g g r e g a t e b l o o d fi l t r a t i o n a n d t h e f e b r i l e t r a n s f u s i o n

reaction: a comparative study. Transfusion 1983;23:95-98

6) Sirchia G, Parravicini A, Rebulla P, Greppi N, Scalamogna M, Morelati F.

Effect iveness of red b lood eel Is fi1tered through cot ton wool to prevent

an t i l eukocy te an t ibody p roduc t ion in mu l t i t rans fused pa t ien ts . Vox Sang

1982;42:190-197

7) Si rch ia G, Parrav ic in i A, Rebul la P, Fat tor i L , Mi lani S. Evaluat ion of

three procedures for the preparation of leukocyte-poor and leukocyte-free red

blood cells for transfusion. Vox Sang 1980;38:197-204

8) Reesink HW, Veldman H, Henrichs HJ, Prins HK, Loos JA. Removal of

l e u k o c y t e s f r o m b l o o d b y fi b r e fi l t r a t i o n : A c o m p a r i s o n s t u d y o n t h e

performance of two commercially available filters. Vox Sang 1982;42:281-288

9) MacNamara E, Clarke S, McCann SR. Provision of leukocyte poor blood at the

bedside. J Clin Pathol 1984;37:669-672

11

Davis - 12

10) Feng CS, de Jongh OS, Bouchette 0, Wallace ME, Kao YS. Evaluation of

cotton-wool filters for preparing leukocyte-poor blood. Lab Med 1984;15:47-49

11) Lichtiger B, del Val le L, Armintor M, Trujil lo JM. Use of Imugard IG500

filters for preparation of leukocyte-poor blood for cancer patients. Vox Sang

1984;46:136-141

12) Johnson J, Mijovic V, Brozovic B. Evaluation of a new filter for leukocyte

depletion of blood. J Clin Pathol 1983;36:1200-1

13) Johnson EJ, Mijovic V, Brozovic B. Further evaluation of a new filter for

leukocyte depletion of blood. J Clin Pathol 1984;37:1415-6

14) Perkins HA, Payne R, Ferguson J, Wood M. Nonhemolytic febrile transfusion

r e a c t i o n s : q u a n t i t a t i v e e f f e c t s o f b l o o d c o m p o n e n t s w i t h e m p h a s i s o n

isoantigenic incompatibility of leukocytes. Vox Sang 1966;11:578-600

1 5 ) Te g t m e i e r G E . Tr a n s f u s i o n - t r a n s m i t t e d c y t o m e g a l o v i r u s i n f e c t i o n s :

significance and control. Vox Sang 1986;51(suppl. l):22-30

16) Yoffe B, Noonan A, Melnick JL, Hollinger FB. Hepatitis B virus DNA in

mononuclear cells. J Inf Dis 1986;153:471-477

17) Hel lings JA. Non-A, non-B hepatitis: an update. Vox Sang 1986;51(suppl.

l ) :63-66

18) Lovric VA, Schuller M, Raftos J, Wisdom L. Filtered microaggregate-free

erythrocyte concentrates with a 35-day shelf life. Vox Sang 1981;41:6-10

19) Wenz B, Gurtlinger KF, 0'Toole AM, Ougan EP. Preparation of granulocyte-

poor red blood cells by microaggregate filtration. Vox Sang 1980;39:282-287

2 0 ) S c h n e d A R , S i l v e r H . T h e u s e o f m i c r o a g g r e g a t e fi l t r a t i o n i n t h e

prevention of febrile transfusion reactions. Transfusion 1981;21:675-681

12

Davis - 13

Table 1: Character ist ics of five leukocyte fil ters tested in vi t ro

Pall: Ultipor SQ40S (Pall Biomedical Products Corp., East Hills, NY). This is

a screen filter of polyester to remove microaggregates; the estimated pore size

is 40 microns. It is designed for use during transfusion, so the unit storage

life is not reduced. Formation of microaggregates is enhanced by spinning and

cooling the unit, thus blood bank personnel t ime is required. Multiple units

may be filtered through one filter. Approximate cost: $5.

Fenwal: 4C 2423 (Fenwal Laboratories, Deerfield, IL). This is similar in use

t o t h e P a l l fi l t e r , b u t i s a d e p t h / s c r e e n fi l t e r w i t h a p o r e s i z e o f 2 0

microns. Single unit capacity. Approximate cost: $6.

Imugard: Imugard IG500 (Terumo Corporat ion, Piscataway, NJ) . This is a

depth/adsorption column filter composed of cotton wool. The filter must be

primed with 300-500 mL of saline, and pressure must be used when filtering

blood. Thus it is designed for use in the blood bank, and the unit storage

l i fe is l imi ted. Single uni t capaci ty. Approximate cost : $10.

Erypur : Erypur g-0 (Organon Teknika Corp. , Oklahoma Ci ty, OK). This is

s i m i l a r t o t h e I m u g a r d fi l t e r , e x c e p t t h a t i t i s c o m p o s e d o f c e l l u l o s e

acetate, and blood may be filtered without pressure. Approximate cost: $15.

Sepacel 1: Sepacell R-500 (Asahi Medical Co. Ltd., Tokyo, Japan; distributed in

the U.S . by Fenwa l Labora to r ies ) . Th is i s an in - l i ne adsorp t ion fi l te r o f

polyester, with an estimated pore size of 20 microns. It is designed for use

dur ing t rans fus ion , so the re i s no l im i ta t ion in un i t s to rage l i f e o r un i t

preparation by the blood bank. Single unit capacity. Approximate cost $14.

13

Davis - 14

Table 2: Comparison of in vitro performance of five leukocyte filters

c

F i l t e r P a l l Fenwal -Imugard Erypur Sepacel1

Published results

(References) (4) (2*) (2,3,6-11) (3,6-9) (12,13)

Reduction WBC (%) 84.4 65 90-98.3 97.9-99 99.7,99.1

Absolute WBC x 109 0.36 0.55 0.02-0.27 0.02-0.14 0.04

Recovery RBC (%) 92.7 73 85.9-97.1 89.4-100+ 89.8,91.1

P la te le ts% removedref. 44.83 63.53 51.08,68.43 87.98,80.93 96.412,83.:

Our results

Single units,number tested

19 2 4 5 10

Reduction WBC (%) 55.0*23.2 66.0*8.5 89.7+9.9 98.1*0.9 97.9*1.9

Absolute WBC x 109 1.03*.60 0.3 4,*. 12 0.51+0.7 0.05+.03 0 .03+.02

Recovery RBC {%) 92.0+9.8 60.5+16.2 92.6*14.0 91.5*8.0 93.1*6.3

Second units,number tested 5 2 1 I t 2t

Reduction WBC (%) 47!0+30.6 26.5*14.8 98 90 97

Absolute WBC x 109 1.35*1.17 1.15*.12 0.05 0.37 0.07*.03

Recovery RBC (%) 91.2*17.3 74.5*13.4 96 86 85.0*1.4

Age at testing indays, range (mean) 1-32 (4.8) 5-9 3-7 3-7 6-18 (9.4)

Values shown are the mean * the standard deviation

*Spun without cooling

^-Unable to complete all units tested

14

Davis - 15

Information on authors

1) R. Eric Davis, M.D., Resident

2) Elizabeth A. Donegan, M.D., Assistant Professor

3) Girish N. Vyas, Ph.D., Professor

Department of Laboratory Medicine

Universi ty of Cal i fornia

San Francisco, CA

j Q $ ^ \

15