Clotting factor product administration and same-day occurrence of thrombotic events, as recorded in a large healthcare database during 2008-2013.

BACKGROUND: Thrombotic events (TEs) are serious adverse events that can occur following administration of clotting factors (CFs). OBJECTIVES: To evaluate occurrence of same-day TEs for different CF products and potential risk factors. METHODS: A retrospective cohort study of individuals exposed to CF products during 2008-2013 was conducted using a large commercial insurance database. CF products were identified by procedure codes, and TEs were ascertained via diagnosis codes. Crude same-day TE rates (per 1000 persons exposed) were estimated overall and by congenital factor deficiency (CFD) status, CF products, age and gender. Multivariable logistic regression analyses were used to control for confounding. Laboratory analysis was used to compare the procoagulant activities of FIX products. RESULTS: Of 3801 individuals exposed to CFs, 117 (30.8 per 1000) had same-day TEs recorded. The crude same-day TE rate was higher for CF users without CFD, 70.2 (102 of 1452), as compared with those with CFD, 6.4 (15 of 2349) (RR, 11.0; 95% CI, 6.4-18.9). For individuals without CFD, a significantly increased same-day TE risk was identified for factor IX complex (OR, 6.92; 95% CI, 3.11-15.40), factor VIIa (OR, 9.42; 95% CI, 4.99-17.78) and other products when compared with fibrin sealant. An increased risk of a TE was found with older age (≥ 45 years), history of TEs and underlying health conditions. The laboratory identified elevated procoagulant activity in Profilnine(®) and Benefix(®) . CONCLUSIONS: The study shows an increased same-day TE risk for CF users without CFD and suggests substantial off-label CF use. The study findings also show elevated same-day TE rates for different CF products and suggest the importance of product properties and patient factors.

Platelet transfusion: a clinical practice guideline from the AABB

BACKGROUND: The AABB (formerly, the American Association of Blood Banks) developed this guideline on appropriate use of platelet transfusion in adult patients. METHODS: These guidelines are based on a systematic review of randomized, clinical trials and observational studies (1900 to September 2014) that reported clinical outcomes on patients receiving prophylactic or therapeutic platelet transfusions. An expert panel reviewed the data and developed recommendations using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) framework. RECOMMENDATION 1: The AABB recommends that platelets should be transfused prophylactically to reduce the risk for spontaneous bleeding in hospitalized adult patients with therapy-induced hypoproliferative thrombocytopenia. The AABB recommends transfusing hospitalized adult patients with a platelet count of 10 × 109 cells/L or less to reduce the risk for spontaneous bleeding. The AABB recommends transfusing up to a single apheresis unit or equivalent. Greater doses are not more effective, and lower doses equal to one half of a standard apheresis unit are equally effective. (Grade: strong recommendation; moderate-quality evidence). RECOMMENDATION 2: The AABB suggests prophylactic platelet transfusion for patients having elective central venous catheter placement with a platelet count less than 20 × 109 cells/L. (Grade: weak recommendation; low-quality evidence). RECOMMENDATION 3: The AABB suggests prophylactic platelet transfusion for patients having elective diagnostic lumbar puncture with a platelet count less than 50 × 109 cells/L. (Grade: weak recommendation; very-low-quality evidence). RECOMMENDATION 4: The AABB suggests prophylactic platelet transfusion for patients having major elective nonneuraxial surgery with a platelet count less than 50 × 109 cells/L. (Grade: weak recommendation; very-low-quality evidence). RECOMMENDATION 5: The AABB recommends against routine prophylactic platelet transfusion for patients who are nonthrombocytopenic and have cardiac surgery with cardiopulmonary bypass. The AABB suggests platelet transfusion for patients having bypass who exhibit perioperative bleeding with thrombocytopenia and/or evidence of platelet dysfunction. (Grade: weak recommendation; very-low-quality evidence). RECOMMENDATION 6: The AABB cannot recommend for or against platelet transfusion for patients receiving antiplatelet therapy who have intracranial hemorrhage (traumatic or spontaneous). (Grade: uncertain recommendation; very-low-quality evidence).(AU)

Febrile non-haemolytic transfusion reaction occurrence and potential risk factors among the U.S. elderly transfused in the inpatient setting, as recorded in Medicare databases during 2011-2012.

BACKGROUND AND OBJECTIVES: Febrile non-haemolytic transfusion reaction (FNHTR) is an acute transfusion complication resulting in fever, chills and/or rigours. Study's objective was to assess FNHTR occurrence and potential risk factors among inpatient U.S. elderly Medicare beneficiaries, ages 65 and older, during 2011-2012. MATERIALS AND METHODS: Our retrospective claims-based study utilized large Medicare administrative databases. FNHTR was ascertained via ICD-9-CM diagnosis code, and transfusions were identified by recorded procedure and revenue centre codes. The study ascertained FNHTR rates among the inpatient elderly overall and by age, gender, race, blood components and units transfused. Multivariate logistic regression analyses were used to assess potential risk factors. RESULTS: Among 4 336 338 inpatient transfusion stays for elderly during 2011-2012, 2517 had FNHTR diagnosis recorded, an overall rate of 58.0 per 100,000 stays. FNHTR rates (per 100,000 stays) varied by age, gender, number of units and blood components transfused. FNHTR rates were substantially higher for RBCs- and platelets-containing transfusions as compared to plasma only. Significantly higher odds of FNHTR were identified with greater number of units transfused (P < 0.01), for females vs. males (OR = 1.15, 95% CI 1.04-1.27), and with 1-year histories of transfusion (OR = 1.25, 95% CI 1.10-1.42), lymphoma (OR = 1.22, 95% CI 1.02-1.46), leukaemia (OR = 1.90, 95% CI 1.56-2.31) and other diseases. CONCLUSIONS: Our study shows increased FNHTR occurrence among elderly with greater number of units and with RBCs- and platelets-containing transfusions, suggesting need to evaluate effectiveness of prestorage leucoreduction in elderly. The study also suggests importance of prior recipient alloimmunization and underlying health conditions in the development of FNHTR.

Irradiation eradication and pathogen reduction. Ceasing cesium irradiation of blood products.

The irradiation of cellular blood components to prevent transfusion-associated (TA)-GVHD is an established practice in the developed world. Susceptible patients include those who are immunosuppressed, fetuses, very premature neonates and patients who have an increased likelihood of possessing one HLA haplotype for which the blood component donor is homozygous. Problems and challenges associated with blood component irradiation include transfusion delay, cost, failure to irradiate when indicated, increased potassium accumulation in and decreased shelf life of RBC units, reduced RBC recovery and, in the United States, substantial and onerous security requirements for cesium-137 source irradiators and their operators. Microbial contamination of blood components can pose life-threatening risks for transfusion recipients. Donor history screening and infectious disease testing are a reactive response and expensive, as well as an imperfect and incomplete means for preventing these infectious risks. In response to these threats, pathogen reduction technologies have been developed. Two such innovations (INTERCEPT, Cerus Corporation, Concord, CA, USA; and Mirasol, CaridianBCT Biotechnologies, Lakewood, CO, USA) are approved for clinical use in many countries, though not in the United States. These processes have been shown to effectively prevent proliferation of nucleic acid-containing microbes, thereby providing broad protection against transfusion-transmitted infection. These technologies have also been shown to prevent the replication of WBC. In this report, we review the substantial in vitro, clinical trial and clinical practice observational evidence that non-irradiated INTERCEPT- and Mirasol-treated cellular blood components do not cause TA-GVHD. Implementation of these processes precludes the necessity for irradiating cellular blood components to prevent TA-GVHD.

Transfusion triggers for blood components.

Whereas there are general guidelines for acceptable transfusion therapy, optimal transfusion therapy has not been determined for most clinical settings. Recent research has focused on controlled studies of red cell transfusion in specific clinical settings. Better determinations of oxygen delivery and consumption are needed to guide clinicians in determining whether transfusion is justified for patients during the perioperative period, those with coronary artery disease, and those in intensive care units. For sickle cell disease, the role of transfusion for acute complications can be life saving; however, the role of chronic transfusion regimens awaits further research into efficacy. Finally, whereas criteria for the prophylactic transfusion of platelets in hematologic diseases are well described, relatively little information is available on the value of platelet transfusion where the absolute count is less than 100,000 but greater than 50,000. The value of fresh frozen plasma components, both standard and sterilized, also requires elucidation.

Fibrin sealant: clinical use and the development of the University of Virginia Tissue Adhesive Center.

The utilization of fibrin sealants to augment hemostasis, seal tissues, and facilitate targeted delivery of drugs is increasing. In 1985, a hospital-based program was established to provide autologous and allogeneic cryoprecipitate that serves as a fibrin sealant when combined with bovine thrombin. To date, more than 4,000 patients have been treated with this product at our institution, with an efficacy rate greater than 90%. Collaboration among surgical services and the blood bank fostered multispecialty expertise with this product that led, in 1997, to the establishment of the University of Virginia Tissue Adhesive Center. The Tissue Adhesive Center is a multidisciplinary center whose physician director and nursing and administrative support staff facilitate basic research, laboratory investigation, and preclinical and clinical trials with collaborators throughout the university. The Tissue Adhesive Center also provides educational programs and clinical consultation, and tracks and participates in peer review of sealant use. The licensure of a commercially produced, virally inactivated, pooled-plasma fibrin sealant in May 1998 provided an alternative source of adhesive. Utilization of the commercial product surpassed use of the blood bank product in April 1999. At present, use of the commercial product is approximately 3 times that of the blood bank-produced sealant. This report reviews the clinical uses of fibrin sealant, its regulatory history, the production of fibrin sealants, the evolution of a blood bank fibrin sealant program, the development of the Tissue Adhesive Center, and the utilization of commercial and blood bank-produced sealant at our university hospital.

Autologous fibrin sealant reduces pain after tonsillectomy.

OBJECTIVES/HYPOTHESIS: Pain is a major cause of morbidity after tonsillectomy. Although various efforts have been made to reduce pain, the use of oral analgesics, which can have adverse side effects, remains the standard of care. It is hypothesized that fibrin sealant, used to achieve hemostasis and enhance healing in many surgical procedures, might help decrease pain after this operation. STUDY DESIGN: A prospective, randomized, blinded study was performed on 20 children aged 5 to 17 years who were undergoing tonsillectomy, to evaluate the efficacy of FIBRIN SEALANT in reducing postoperative pain. METHODS: All patients pre-donated 40 mL of blood from which autologous concentrated fibrinogen was prepared by cryoprecipitation. In the fibrin sealant group, fibrinogen and topical bovine thrombin were sprayed onto the surgical site to form fibrin sealant at the conclusion of tonsillectomy. The 10 patients in the control group (C) received no fibrin sealant. Patients rated their level of pain immediately after surgery and at regular intervals for 3 days after surgery using the Wong-Baker Faces Pain Rating Scale (1-6). Emesis, postoperative bleeding, medications, and adverse events were also evaluated. RESULTS: At 7.00 P.M. on postoperative day (POD) 0, the mean +/- SD fibrin sealant group pain score (2.9+/-0.41 units) was significantly lower than for the C group (4.1+/-0.43 units; P < or = .05). There was also a trend in favor of less pain in the fibrin sealant group at 7:00 P.M. on POD 1, with a mean of 3.5+/-0.43 units versus 2.4+/-0.48 units for C (P = .15). The odds of a patient in C experiencing emesis were 8.16 times higher, (P < or = .05) than for patients in the fibrin sealant group. CONCLUSIONS: Fibrin sealant significantly reduced pain the evening after pediatric tonsillectomy and also decreased the chance of experiencing emesis. Thus fibrin sealant may be clinically useful as an adjunct to tonsillectomy.

MAM: a "new" high-incidence antigen found on multiple cell lines.

BACKGROUND: Three women have been identified with an antibody to a "new" high-incidence antigen found on multiple cell lines. CASE REPORTS: The proposita, M.A.M., presented during her third pregnancy with an antibody reacting with all RBCs tested except her own. She delivered a thrombocytopenic infant with a 3+ DAT, but without symptoms of HDN. The second example, A.N., presented during her third pregnancy with an antibody reacting with all RBCs tested except her own and those of M.A.M. She delivered a slightly thrombocytopenic but severely anemic infant. The third example, F.K., a sister of A.N., has an antibody reacting with all RBCs tested except her own and those of M.A.M. and A.N. CONCLUSION: This "new" high-incidence antigen has been named MAM and assigned high-incidence antigen number 901016 by the International Society of Blood Transfusion. The corresponding antibody, anti-MAM, has been shown to cause HDN and has the potential to shorten RBC survival after the transfusion of incompatible RBC units, as determined by monocyte monolayer assay. Immunoblotting and flow cytometry show that this new antibody reacts with various WBC lines in addition to RBCs. This antibody also appears to react with platelets in some assays.

Hemolysis during leukocyte-reduction filtration of stored red blood cells.

Hemolysis has been reported in red blood cells (RBCs) that have undergone leukocyte-reduction filtration. This study investigated whether the age of RBCs or the filter type affected hemolysis. One hundred eighty units of RBCs (adenine-saline added) were leukocyte-reduced by filtration. At each of the 6 weeks of shelf life, 10 units were filtered with the "BPF4" filter, 10 units with the "Purecell RCQ" filter, and 10 units with the "Sepacell" filter. Filtration was performed with strict adherence to the manufacturers' directions. Pre- and post-filtration samples were assayed for plasma hemoglobin by measuring the plasma absorbances at 578 nm and 562 nm. The increase of plasma hemoglobin concentration following filtration was significantly greater (p < 0.05) in older units, compared to fresher units, when the Sepacell and BPF4 filters were used. For example, the increase of plasma hemoglobin at week 6 (83.47 mg/dl:Sepacell, 128.93 mg/dl BPF4) was significantly greater than at week 1 (7.07 mg/dl Sepacell, 4.77 mg/dl BPF4) (Sepacell: p=0.008; BPF4: p=0.006). For units stored 1, 2, 4, 5, or 6 weeks, the increase of plasma hemoglobin concentration post-filtration was significantly greater with the BPF4 filter, compared to the Purecell RCQ filter (p <0.045); for units stored 5 weeks, the increase in plasma hemoglobin concentration post-filtration was significantly greater with the BPF4 filter compared to the Sepacell filter (p = 0.009). Mean filtration times were significantly longer in older units compared to fresh units. This study shows that increased storage duration of RBCs (adenine-saline added) is attended by greater hemolysis during leukocyte-reduction filtration and by prolongation of the filtration time. In addition, the amount of hemolysis may be influenced by the type of filter.

A fully automated blood typing system for hospital transfusion services. ABS2000 Study Group.

BACKGROUND: The results of routine blood bank testing by a fully automated blood typing system (ABS2000) were compared with those obtained by standard manual methods in six hospital transfusion services. STUDY DESIGN AND METHODS: The ABS2000 system uses microtiter plates for determining ABO and D types, solid-phase red cell adherence (SPRCA) assays for antibody detection, and modified SPRCA plates for IgG crossmatches. The transfusion services used their standard manual test tube methods. RESULTS: Of 3779 donors' samples tested for ABO types (red cell typings only), 3.0 percent could not be interpreted by the ABS2000 system's neural network, because of clots, hemolysis, or lipemic samples. The results for ABO types were concordant for 99.8 percent of the remaining samples. Of 3779 donors' samples tested for D types, the results were concordant for 98.7 percent. Of 7580 patients' samples tested for ABO types (red cell and plasma typings), 5.8 percent could not be interpreted by the ABS2000 system. There was 100-percent concordance of ABO typing results for the remaining 7140 samples. There was 99. 7-percent concordance of results for patients' D types. The results of 96.7 percent of antibody detection tests and 98.8 percent of crossmatches were concordant. Neither method failed to detect a serologically incompatible crossmatch that was associated with a specific, clinically significant alloantibody. The ABS2000 system performed 45 confirmatory donor ABO and D types in 115 minutes, 22 antibody detection tests in 116 minutes, 16 patients' ABO/D types in 149 minutes, and 40 crossmatches in 140 minutes. CONCLUSION: The ABS2000 blood typing system automates routine blood bank tests with accuracy comparable to that of hospital transfusion services' standard manual methods.

Rapid preparation of small-volume autologous fibrinogen concentrate and its same day use in bleb leaks after glaucoma filtration surgery.

The authors evaluated small-volume preparation of autologous fibrin glue (AFG) and same day use in postglaucoma filtration surgery patients with Seidel positive bleb leaks and determined fibrinogen concentrations in autologous fibrinogen concentrates (AFCs) from 10 volunteers. Thirty milliliters of blood was centrifuged (5 min, 2400 x g); plasma was frozen (5 min-ethanol and ice), thawed (1-6 C, 30-60 min), and centrifuged (10 min, 5 C, 2800 x g); and the precipitate was transferred to a 1.0-ml tuberculosis syringe. Thrombin (1000 U) was dissolved (0.8 sterile water, 0.2 ml aminocaproic acid) and warmed (37 C). Average preparation time was 90 minutes. Alternating drops of AFC and thrombin were applied to bleb leaks until AFC clotted. Seidel testing with fluorescein determined success. AFC was prepared from 10 volunteers and fibrinogen was measured. AFG was initially successful with two (Seidel negative) eyes; one eye remained negative. AFG was unsuccessful in one briskly Seidel-positive leak. Mean +/- SD fibrinogen concentration in AFCs from the 10 volunteers was 2314 +/- 643 mg/dl (range 1608-3431 mg/dl). AFG may successfully close bleb leaks in outpatient settings. Brisk aqueous flow may impair effectiveness of AFG. Fibrinogen concentrations were comparable with previous reports.

Fibrin sealant: an evaluation of methods of production and the role of the blood bank.

Blood banks can prepare fibrin sealant by several methods. Allogeneic components allow for banking of the fibrinogen concentrate for immediate use. Autologous components eliminate the risk of transfusion-transmitted disease to the recipient, but not necessarily to the preparer. Ethanol and ammonium sulfate precipitation of fibrinogen concentrate allow use of autologous blood and fast preparation (less than 90 minutes). Cryoprecipitation from liquid plasma is adequate, conserving fresh frozen plasma. Cryoprecipitation by the "freeze-thaw" method has been reported to have the highest fibrinogen yield (7840 mg/dL +/- 1800 mg/dL), whereas ammonium sulfate precipitation has been reported to have the highest bonding strength (41 g/cm2 10 minutes after thrombin addition). Cost, storage, preparation time, and transfusion-transmitted disease all play a role in choice of method.

Evaluation of CAPTURE CMV solid phase testing over the allowable shelf-life of red blood cells (adenine-saline added).

BACKGROUND: CAPTURE CMV (IMMUCOR Inc., Norcross, GA) is a solid-phase screening test used to detect IgM and IgG antibodies to cytomegalovirus (CMV). CAPTURE CMV is licensed for testing whole blood (WB) in citrate phosphate dextrose (CPD) preserved segments of units of red blood cells (RBC) only up to 7 days of storage. We determined if CAPTURE CMV could produce consistent results in CPD preserved WB segments from RBC adenine-saline added (ASA) for their 42 day shelf-life. METHODS: Ten CMV-seropositive and 10 CMV-seronegative RBC (ASA) tested by CAPTURE CMV during the first week of storage were studied. Segments were tested weekly for 6 weeks. RESULTS: All 10 units that initially tested as CMV-seropositive remained strongly seropositive. All 10 units initially CMV-seronegative, remained seronegative. CONCLUSION: CAPTURE CMV testing provides consistent results over the entire shelf-life of RBC (ASA).

Effects of gamma irradiation on red cells from donors with sickle cell trait.

BACKGROUND: Transfusion-associated graft-versus-host disease can be prevented by gamma irradiation of blood components. Red cells (RBCs) from sickle cell disease patients may exhibit oxidative changes of RBC membranes due to the instability of hemoglobin (Hb) S. Persons with sickle cell trait are eligible to donate blood, and 35 to 45 percent of their total Hb is Hb S. The effect of gamma irradiation on RBCs from such persons is of interest. STUDY DESIGN AND METHODS: RBCs from 12 donors with sickle cell trait (Hb AS) and from 12 with normal Hb (Hb AA) were studied. Each of the 24 RBC units was divided equally into two transfer bags via a sterile connecting device. One bag from each RBC unit received a 2500-cGy dose of gamma irradiation at its mid-plane and was stored at 4 degrees C; the second set of bags was stored without irradiation. For RBCs from 6 donors with Hb AS and 6 donors with Hb AA, units were irradiated on Day 7 and studied on Day 35 of storage (Group 1). For the RBCs from the other 6 donors with Hb AS and the other 6 donors with Hb AA, units were irradiated on Day 28 and studied on Day 42 of storage (Group 2). RESULTS: For Group 1 and Group 2, plasma potassium and plasma Hb concentrations were significantly higher and RBC ATP concentrations were slightly lower in the irradiated units than in the nonirradiated units. In Group 1 and Group 2, there were no significant differences in the plasma potassium or RBC ATP concentrations in either the irradiated or the nonirradiated units of RBCs from donors with Hb AS and donors with Hb AA. Plasma Hb concentrations were consistently lower in the units from donors with Hb AS, whether or not they were irradiated. However, in both groups, proportionally similar changes in plasma Hb concentration were detected when the irradiated Hb AS and Hb AA units were compared to nonirradiated Hb AS and Hb AA units. CONCLUSION: Gamma irradiation of RBCs from donors with Hb AS or with Hb AA resulted in comparable changes in plasma potassium, RBC ATP, and plasma Hb concentrations, although donors with Hb AS had lower plasma Hb. RBCs from donors with Hb AS subjected to 2500 cGy of gamma irradiation did not evidence a storage lesion greater than that seen in RBCs from donors with Hb AA.

Rejuvenation of irradiated AS-1 red cells.

BACKGROUND: Gamma irradiation of blood components is used to prevent transfusion-associated graft-versus-host disease. The demand for irradiated blood components is increasing because of the increase in directed donation by family members. Irradiated units currently have a recommended maximum storage life of 28 days. Since in vivo recovery is related to red cell ATP levels, rejuvenation of stored irradiated units using a pyruvate-inosine phosphate-adenine additive was explored. STUDY DESIGN AND METHODS: Units of AS-1 red cells from 16 volunteer donors were divided into two equal volumes and one split unit from each was irradiated with 25 Gy. Ten units were irradiated on Day 5, 6, or 7 of 4 degrees C storage and 6 units were irradiated on Day 1 of 4 degrees C storage. All units were rejuvenated for 1 hour at 37 degrees C using a pyruvate-inosine-phosphate-adenine additive on Day 42 of 4 degrees C storage. Units were assayed for ATP, 2, 3 DPG and supernatant sodium, potassium, and glucose. RESULTS: ATP and 2, 3 DPG levels were restored equally well in irradiated and non-irradiated units. The previously reported irradiation-induced red cell potassium-sodium shift was demonstrated. Supernatant potassium and sodium levels did not reverse 1 hour after rejuvenation was completed. There was no significant difference in results between units irradiated on Day 1 or Day 5, 6, or 7. CONCLUSION: Red cell ATP and 2, 3 DPG levels were restored in irradiated AS-1 units stored at 4 degrees C for 42 days using a pyruvate-inosine-phosphate-adenine rejuvenation additive.

Comparison of platelet loss during leukocyte reduction at 4, 24, and 48 hours postcollection using a Closed System Apheresis Kit with Integral filter.

Prestorage leukocyte reduction of platelet concentrates may reduce adverse effects of transfusion while affording better quality control. Platelets and leukocytes may undergo activation during storage, which could affect the performance of leukocyte reduction filters. The purpose of this study was to evaluate the efficiency of leukocyte reduction and concomitant platelet loss with a new apheresis kit with an integral leukocyte reduction filter. Twelve donors underwent plateletpheresis on three occasions using the CS-3000 PLUS Blood Cell Separator with the Access Management System and the Access Closed System Apheresis Kit with Integral Sepacell Leukocyte Reduction Filter and Double Return Line Needle (Baxter-Fenwal Division, Deerfield, IL). Of the three products from each donor, one each was filtered at 4, 24, and 48 hours after completion of the plateletpheresis. Mean prefiltration platelet count was 4.43 x 10(11) and mean postfiltration platelet count was 3.56 x 10(11). Mean platelet recovery at 4, 24, and 48 hours filtration was 75%, 83%, and 84%, respectively. Analysis of variance (ANOVA) demonstrated that platelet recovery with filtration at four hours was significantly less than with filtration at 24 hours (P = 0.0236) and filtration at 48 hours (P = 0.0122). Platelet recovery with filtration at 24 hours did not differ significantly from filtration at 48 hours (P = 0.7684). Mean prefiltration WBC count was 0.93 x 10(6) and mean postfiltration WBC count was 0.12 x 10(6). Efficiency of leukocyte reduction was not significantly related to when filtration was performed. There was no significant variation from donor in platelet recovery or in leukocyte reduction efficiency. This method of prestorage leukocyte reduction demonstrated slightly but statistically significantly better platelet recovery with filtration at 24 or 48 hours after platelet collection compared to four hours. All filtration times provided acceptable platelet yields with very low residual WBC.