Nichols, William L.

Abstract Introduction Type 1 von Willebrand disease (VWD 1) accounts for ~75% of VWD. The National Heart, Lung, and Blood (NHLBI) VWD guidelines recommend VWF:Ag and VWF:RCo cut-off levels of <30 (IU/dL or %) for definite laboratory diagnosis of VWD 1. However, guidelines indicate that patients with "low VWF" (VWF:Ag and VWF:RCo in the 30-50 IU/dl range) could be candidates for agents to increase VWF levels if they are at risk for bleeding. Here we examine the diagnostic practices for VWD at Mayo Clinic Rochester by determining the proportion of patient currently classified as VWD 1 that meet NHLBI criteria for "low VWF". In addition, we assess changes in the laboratory phenotype of the aging population of patients with "low VWF" and VWD 1. Methods Patients with a diagnosis of VWD 1 at our institution were identified through our institutional hemophilia treatment center database (1986 to 2017). All available VWF:Ag and VWF activity (ristocetin cofactor assay [VWF:RCo] and latex immuno-activity assay [VWF:Ab]) levels performed at our institution and available in our electronic medical record (EMR) were recorded. Exclusion criteria included confounding variables known to effect VWF levels (eg,. hormonal therapy, pregnancy, desmopressin, or VWF/VIII concentrate administration) at the time of first laboratory assessment (VWF:Ag and VWF activity (by either VWF:Ab or VWF: RCo) at our institution. Bleeding score, retrospectively assessed using the MCMDM-1 VWD bleeding assessment tool (BAT), at the time of first clinical evaluation was recorded if enough information was available in the EMR. All VWF testing was recorded for comparative analysis between the first and the most recent measurements within the study period. Patients were not included in age-related analysis if the most recent laboratory values were obtained in the presence of the confounding variables noted above. Statistical analysis was performed using JMPfor paired t-tests and STATA for multilevel mixed-effects regression analysis. Results 78 patients (50 F) met study criteria. Median age at initial presentation at our institution was 27.5 (0-75) years. Medians (ranges) for VWF:Ag (n=78), VWF:Ab (n=41), and VWF:RCo (n=75) were 39 (5-60)%, 37 (19-53)%, and 36 (11-62)%, respectively (reference ranges 55-200% for VWF and factor VIII values). Coagulation factor VIII activity (FVIII:C) was 63 (10-122)% (n=78). Of 37 patient with available blood type results, 23 (62%) were blood group O. 56% of patients (n=44) met NHLBI criteria for classification as "low VWF" (Figure 1, Panel A). There was no difference in bleeding score between patients with VWD 1 (median bleeding score: 4 (0-14), n=22) compared to those with "low VWF" (median bleeding score: 4 (0-14), n=37). 54 patients had repeat laboratory testing at 4.5 (0-29) years after initial testing. VWF antigen and activity levels were compared in those who had repeat testing done >1 year (n=36) after initial lab testing at our institution. Median age of patients at time of most recent measurement was 42.5 (5-87) years compared to 35.5 (0-75) years at first measurement. VWF:Ag was significantly higher in the most recent measurement compared to the first measurement (p< 0.05, Figure 1, Panel B ). There was no statistically significant difference between VWF activity levels in the first versus the most recent measurement. There was a non-significant trend towards increasing VWF:Ag with increasing age; however when stratified into "low VWF" and VWD 1 disease groups, there was a significant relationship between VWF Ag and age in the "low VWF" group with mixed effects regression model (coefficient: 0.207, p:0.043). Conclusion Approximately 55% of patients with a clinical diagnosis for VWD 1 meet criteria for "low VWF." In our cohort, there was no difference in bleeding (BAT) scores between the two groups; however our analysis is limited by its retrospective nature. We also demonstrate a statistically significant increase in VWF:Ag with aging; however, with regression analysis, this change was only noted in those in the "low VWF" group. Larger prospective studies controlling for confounding factors are needed to further demonstrate the effect of age on VWF antigen and activity levels. Disclosures No relevant conflicts of interest to declare.

Abstract Background Platelet dense granule (DG) deficiencies, including Hermansky-Pudlak syndrome, are relatively common and frequently under-diagnosed hereditary platelet hypofunctional disorders. Among various laboratory tests, platelet whole mount (WM) transmission electron microscopy (TEM) is considered the gold standard method for diagnosing DG deficiencies. Nevertheless, platelet DG TEM testing is still largely a research tool and has not been thoroughly validated and standardized as a clinical test. Furthermore, reference ranges (RR) of DG count/platelet (DGC) have not been adequately established. Aim Our goals were to validate and standardize platelet WM TEM testing and establish reference ranges for platelet DGC. Methods Based on previously established methods (Blood, 33:598-606), we first optimized and standardized various pre-analytical, analytical and post-analytical procedures including sample matrix, sample stability, platelet-rich plasma (PRP) preparation, platelet mounting procedure and DG counting criteria. Then whole blood samples in ACD-B tubes were collected from a total of 128 healthy donors (64 males and 64 females). Platelet DGC, percentage of platelets without any DG (empty platelets), platelet count (PC), mean platelet volume (MPV) and immature platelet fraction (IPF) were measured. In addition, platelet aggregometry analyses were performed on citrated PRP samples from the same donors. Standard statistical analyses were employed in this study. Results DGC and platelet ultra-structure were stable when whole blood samples were stored at room temperature (RT) for up to 4 days. Reproducible DGC and adequate preservation of platelet ultrastructure depended on an optimized mounting method. The DG counting criteria were developed based on previous publications and guidance from Dr. James G. White. Using the same WM TEM images and DG counting criteria, agreements among different technologists (n=5) improved from 60% to 95%. Finally, DGC reference range study using 128 healthy donor samples (age range 18, 72 years) and scoring 100-200 platelets from each donor showed that the DGC distribution of each donor sample was left-skewed with a median of 15% of empty platelets (range: 3, 40). The median DGC was 2.6 with a range of 1.0—5.1. Reference ranges established at the lower 95th percentile for DGC empty platelets is ≤ 31% (95% CI 28, 34) and for the mid-95th percentiles of DGCs between 1.5 and 4.0. DGCs were weakly associated with MPV and IPF (ρ between 0.22 and 0.28); and inversely associated with the percentage of empty platelets (ρ between -0.26 and -0.25). DGC showed no significant association with PC, platelet maximum aggregation or primary slope of aggregation, nor age or gender. Conclusion We validated platelet WM TEM procedures and for the first time established an adult reference range for platelet DGC. The results of association analyses implied that immature platelets may have slightly more DGs. Disclosures: No relevant conflicts of interest to declare.

Abstract Accurate measurement of plasma von Willebrand factor (VWF) activity is essential for the laboratory diagnosis and treatment monitoring of von Willebrand disease (VWD). Currently available VWF activity assays include VWF ristocetin cofactor activity by manual light transmission platelet aggregometry (VWF:RCo–Agg) or flow cytometry (VWF:RCo–FL), collagen I and III binding activity (VWF:Co–I and –III) (Technozym), and platelet activity by latex agglutination (VWF:Lx) (Instrumental Laboratory). In this study we evaluated and compared the accuracy and precision of these 5 assay methods. Plasma samples from 11 normal donors and 41 patients categorized as type 1 (n=20) or type 2 (n=21) VWD based on clinical evaluation, fVIII:C activity, VWF:RCo–Agg, VWF antigen (VWF:Ag) level and plasma VWF multimer analysis by agarose gel electrophoresis were assayed for VWF activity by VWF:RCo–FL, VWF:Co–I, VWF:Co–III and VWF:Lx methods. The VWF:Ag/VWF activity ratio by VWF activity assay method was calculated for each sample. For normal donors and type I VWD patients, VWF:RCo–FL and VWF:Lx correlated well with VWF:RCo–Agg (R2=0.87, and 0.97, respectively), while VWF:Co–I and –III were lower compared to VWF:RCo-Agg. For type 2 VWD patients, different VWF:Ag/VWF activity ratio cutoffs (range 0.3–0.7) were used (Figure). Both VWF:RCo–Agg and –FL were sensitive (95%) and specific (97%) for type 2 VWD while the VWF:Lx was slightly less sensitive (81%) but was very specific (100%). VWF:Co–I and –III were the least sensitive (<90%) and specific (<90%); both methods had high false positive and negative rates for type 2 VWD. In Summary, for normals and type 1 VWD patients, VWF:RCo–FL and VWF:Lx correlate well with VWF:RCo–Agg and have similar sensitivities and specificities for type 2 VWD. VWF:Co–I and –III are unreliable for assessing plasma VWF activity.

Abstract Abstract 2279 Surgery for patients with von Willebrand disease (VWD) is increasingly common, however there is a paucity of data on hemostatic outcomes for VWD patients undergoing joint replacement surgery when compared to patients without bleeding disorders. The aim of this study was to evaluate hemostatic prophylaxis and outcomes in VWD patients who underwent hip or knee joint replacement, with comparison to matched case control patients. Methods: We retrospectively reviewed medical records of VWD patients who underwent total hip (THA) or total knee (TKA) arthroplasty between February 1993 and January 2011 at Mayo Clinic Rochester. Outcomes for each VWD patient were compared with two case controls matched for age, gender, surgeon and surgery. For VWD patients the hemostatic prophylaxis regimen during and following surgical procedures was evaluated including results of serial monitoring of plasma levels of VWF:RCo, VWF:Ag and FVIII:C. We compared VWD and control cases for bleeding complications (major and minor), transfusion requirements, DVT (deep vein thrombosis) prophylaxis and occurrence, duration of hospitalization, and other complications. Results: Twelve VWD patients (7 female) underwent 12 TKA and 7 THA surgeries; the median age was 62 (range 42–76) years. Seven had Type 1 VWD, one had Type 3 and four had Types 2A, 2B or 2M VWD. The 19 surgical episodes were matched to 38 control surgeries. Indications for arthroplasties were mainly degenerative joint disease in both subject groups. The median BMI was 30 (range 21–45) in the VWD patients and 31.9 (20–53) in controls. Three patients with mild Type 1 VWD received during 5 surgeries only one preoperative dose of DDAVP (desmopressin 0.3μg/kg body weight). Infusions of VWF/FVIII concentrates (Humate-P or occasionally Koate-DVI) were prescribed for twelve procedures, with median preoperative dose 52 IU/kg (range 19–71). Postoperative maintenance doses were infused once or twice daily usually for up to 7 days (more than 7 days only for one Type 3 and one Type 2A VWD patient), with median ranges 22 to 38 IU/kg, and highest dose 90 IU/kg and lowest dose 11 IU/kg (typically when treatment was administrated twice daily). These substantial ranges may be explained by dose adjustments based on monitoring postoperative plasma levels of VWF:RCo and FVIII:C. The median number of infusions per procedure was 5.5 (range 1–13). One hour after the preoperative dose the median of all factors was more than 110 IU/dL, specifically VWF:RCo 154 UI/dL (range 72–277), VWF:Ag 178 IU/dL (range 101–307), and FVIII:C 114 IU/dL (range 64–290). The lowest factor levels measured during daily postoperative follow-up are represented in Figure 1. Assessment of red blood cell transfusion requirements showed no difference between baseline and D1 blood hemoglobin levels for VWD and control groups (decline of 3.0 g/dL). During follow-up, hemoglobin levels and total blood losses were also not different between both groups. However, the number of patients transfused was twice as high for the VWD group (63% vs 32% for controls, respectively), and the mean number of RBC units transfused was higher in VWD patients than in controls (1.5 vs. 0.6 units, respectively). DVT prophylaxis (low molecular weight heparin (LMWH) injections or warfarin), was administrated to 58% of VWD patients vs. 97% of controls. No postoperative thrombotic events were identified in either group. Finally, the median duration of hospitalization for VWD patients and controls was not different: 5 days (range 3–13) and 5 days (range 3–7) respectively. Conclusions: Few data are available in published literature analyzing treatment regimens and hemostatic outcomes for patients with VWD undergoing THA or TKA, a relatively common treatment for advanced degenerative joint disease. This is the first large retrospective study which reports the effectiveness of prophylactic regimens specifically in joint replacement for patients with VWD. Our results support that, as recommended in the 2008 NHLBI/NIH treatment guidelines, monitoring of plasma VWF and FVIII levels at least once daily allows for efficient and relatively low dose maintenance administration. Further, our study helps identify an adequate duration of treatment for these major surgeries, without substantively increased blood loss for VWD patients compared with controls. Disclosures: No relevant conflicts of interest to declare.

Abstract Introduction: Gardner-Diamond Syndrome (GDS), also known as psychogenic purpura, is a rare disorder characterized by unexplained recurrent painful bruising typically arising after physical and/or psycho-emotional stress. Classically ecchymoses (ecch) spontaneously appear and are associated with a prodrome of warmth and pain at the ecch sites. Prior GDS reports are limited to single cases or small series. Aims:To characterize presentation, natural history, management and long term outcomes (LTO) of GDS. Methods: In this retrospective study, after IRB approval, patients (pt) with GDS, encountered between 1976 and 2016, were identified from within Mayo Clinic Rochester clinical databases. Medical records of consenting pts were reviewed. Results: 75 females (ages 16-69 years (yr)) and 2 males (46-65 yr) met our study criteria. Pt presented 3.2 yrs (range 0-27) after onset of initial symptoms (sym). 52 pt (67.5%) had an antecedent history of physical abuse (n=2), trauma (n=12), an emotional event (n=13), surgery (n=11), or infection (n=3). Prodromal sensations prior to appearance of ecch in 55 pts (71.4%) were described as itching (n=15), burning (n=19), stinging (n=11), and/or pain (n=44). Other localized sym after appearance of ecch included swelling (n=46) and pain (n=67). Maximum size of ecch ranged from >0 and ≤5 cm (n=26), ≥6 and ≤ 10 cm (n=14), and >10 cm (n=13) and not described in 24 pts Systemic sym at time of ecch, reported in 49 pts, included malaise (n=26), myalgia (n=21), headaches (n=19), fevers (n=15), and abdominal pain (n=10). 50 (65%) of pts' lesions were isolated to arms and legs, while 27 (35%) had trunk and head involvement in addition to extremity involvement. Ecch duration varied: 0-7 days (n=14), 1 week-1 month (n=31), or >1 month (n=5) and not described in 27 pts. Complete blood count was normal (nl) in 84% (64/76) of pts tested; anemia was the most common abnormality. PT, APTT, VWF, and Factor XIII screen were nl in 100% (67/67), 98.4% (63/64), 97.9% (46/47), and 100 % (30/30) of pts respectively. Platelet aggregation studies were nl in 83% (25/30) with abnormalities attributed to drug effect. Bleeding (bld) scores (ISTH BAT), calculated with exclusion of cutaneous (cut) manifestations in scoring, were: 0 (n=48), 1 (n=12), 2 (n=9), 4 (n=2), 5-6 (n=2), 7 (n=2), and 9 (n=2). 21 pts had testing with subcut injections of autologous red cells (SCIAR) with 9 positive and 2 equivocal. 28 pts had skin biopsies with the most common finding being subcut hemorrhages. 45 pts (58.4%) underwent psychiatric (psych) evaluations and 7 (15%) pts were found not to have a psych dx. 42 pts had a psych dx including depression (n=23), hysterical personality (n=8), anxiety (n=2), personality disorder (n=2), psych other (n=7). Of these pts, 4 did not undergo further psych eval given prior dx. 42 pts had a history of a neurological dx including headaches (n=34), paresthesias (n=10), and seizures (n=7). Additional pharmacological treatments (pharmt) were recommended for 30 pts: antidepressants (n=4), antihistamines (n=13), anti-inflammatory/immunosuppressants (n=11), or hormonal (n=2) medications. 47 pts were treated with observation and/or counseling alone to address psychological stressors. 28 pts had follow-up (fu) at least 1 yr (1 to 34 yrs) after the initial visit. 13 of these pts had no mention of recurrence during fu while 15 pts had continued recurrence. Of those with recurrence, 7 pts continued to seek fu for GDS. Conclusion: In this large clinical cohort of GDS pts we confirm and expand on known clinical findings of GDS. Majority of pts had fairly benign disease (dz) manifestations; however, in a subset, a negative impact on pt quality of life was noted due mainly to persistent/recurrent pain. Refractory dz was mostly associated with ongoing/ recurrent stressors. The relatively low bld scores, together with laboratory assessments, support that GDS is primarily a dermal rather than a systemic bld diathesis. SCIAR did not provide additional value in dx. CBC, PT, APTT & VWF testing should be performed, and platelet testing considered, to rule out other hemostatic dz. Addressing stressors was the most effective treatment for pts, however pharmt was given for refractory dz. Though our study provides new insights regarding dx, therapy and LTO, future work investigating the pathophysiology leading to the hemostatic abnormalities in GDS would be valuable. Disclosures No relevant conflicts of interest to declare.

Abstract Background Congenital/hereditary qualitative platelet disorders (CQPD) can be classified by platelet count (eg, normal or decreased) and platelet size as well as by functional defect. Based on mean platelet volume (MPV), congenital thrombocytopenias (CT) are classified as macro-thrombocytopenias (eg, Bernard-Soulier syndrome [BSS], MYH-9 [myosin heavy chain 9, non-muscle]-associated thrombocytopenias, gray platelet syndrome [GPS], etc.); microthrombocytopenias (eg, Wiskott-Aldrich syndrome and variants); and those with normal platelet size. CQPDs with normal platelet count include Glanzmann thrombasthenia (GT), dense granule storage pool disorders (DG-SPD) including Hermansky-Pudlak syndrome (HPS), platelet secretion disorders and many others. Diagnosis has relied on platelet counting and sizing, blood smear light microscopy, platelet aggregation (agg) and platelet function analyzer (PFA-100) studies. Platelet transmission electron microscopy (PTEM) and flow cytometry can provide supplementary information and molecular analysis is also evolving. The objective of this study was to determine the roles of platelet transmission electron microscopy (PTEM) and flow cytometry in the diagnosis of CQPD and CT. Methods In this retrospective cohort study, after IRB approval, the electronic medical record system was queried for patients (pt) with a confirmed CQPD or CT seen at Mayo Clinic between 2000 and 2015. A detailed chart review was undertaken. Results 54 pt (64% female) met our study criteria; median age was 32 years (range 1 day to 81 years). 18/54 (33%) pt had macrothrombocytopenia: BSS 4 (7%); MYH-9 10 (19%); gray platelet syndrome 4 (7%). 36/54 (66%) had normal MPV: Glanzmann thrombasthenia 6 (11%); storage pool disorders including DG-SPD 10 (19%) and HPS 2 (3%), mild alpha granule deficiency 3 (6%) and York platelet syndrome 4 (7%); platelet secretion disorders 4 (7%); ANKRD26 mutation 3 (6%); congenital amegakaryocytic thrombocytopenia 1 (2%); GATA-1 mutation 1 (2%); RUNX-1 mutation 1 (2%); and Jacobsen syndrome 1 (2%). 44 pt (81%) had a positive bleeding history: epistaxis 52%, cutaneous bleeding 57%, gastrointestinal bleeding 21% and menorrhagia 54%; 10 pt (19%) had a negative bleeding history. Results of standard and esoteric platelet testing are summarized in Table 1. Diagnosis in the 10 pt with glycoprotein deficiency (BSS or GT) was established by agg; flow cytometry was confirmatory but not necessary. Of the 23 pt with SPD, 5 had a negative bleeding history; 4 pt had normal agg and PFA-100 and were diagnosed exclusively by PTEM. In this group, the abnormalities on platelet aggregation and PFA were variable and PTEM allowed for a better definition of the specific abnormalities. For MYH-9 patients, PTEM confirmed leukocyte inclusions that had already been identified on light microscopy. PTEM was the only diagnostic modality able to identify the abnormality in York platelet syndrome. In 5/54 (9%) genetic testing was necessary for diagnosis (GATA-1, ANKRD26 and RUNX-1) Conclusion In this cohort, standard platelet assays established the diagnosis in the large majority of CQPD and CT. PTEM was essential for confirmation in DG-SPD, mild alpha granule deficiency and York platelet syndrome and useful in combination with molecular testing to establish a diagnosis in selected cases. Guidance on selection of patients for such specialized testing requires further study. Table 1. Results of standard and esoteric platelet testing for 54 patients with congenital qualitative platelet disorders and/or thrombocytopenia Disorder n (%) Platelet aggregation PFA PTEM Flow cytometry Confirmation by genetics Done Abnormal Done Abnormal Done Abnormal Done Abnormal Glanzmann thrombasthenia 6 (11) 6 6 5 5 1 0 3 3 0 Bernard-Soulier syndrome & variants 4 (7) 4 4 4 4 3 0 4 4 0 MYH-9 related disorders 10 (19) 7 2 8 3 5 5 4 2 5 Dense granule deficiency and HPS 12 (22) 12 8 12 8 12 12 4 0 0 Alpha granule deficiency* 7 (13) 7 4 7 6 7 7 4 4 1 York platelet syndrome 4 (7) 1 0 1 1 4 4 1 1 0 TXA2 or PG synthesis/receptor defect 4 (7) 4 4 4 3 3 0 3 0 0 CATM 1 (2) 0 - 0 - 0 - 0 - 1 ANKRD26 3 (6) 3 3 3 2 3 3 3 3 3 GATA-1 1 (2) 0 - 1 1 1 1 1 1 1 RUNX-1 1 (2) 1 0 1 1 0 - 0 - 1 Jacobsen syndrome 1 (2) 1 0 1 1 1 1 1 0 1 MYH-9: myosin heavy chain 9, non-muscle (MHY-9) associated thrombocytopenia, HPS: Hermansky-Pudlak Syndrome, TXA2: thromboxane A2, PG: prostaglandin CATM: congenital amegakaryocytic thrombocytopenia. * Includes gray platelet syndrome Disclosures Pardanani: Stemline: Research Funding.

Diagnosis of Bernard-Soulier syndrome (BSS) is complicated by the difficulty of separating the giant platelets from other blood cells to pursue analyses of platelet function and structure. We report on the utility of three whole blood assay techniques for diagnosis of a patient with BSS. To our knowledge, these three techniques have not been simultaneously applied or compared for efficacy in laboratory diagnosis of BSS. (1) Whole blood platelet aggregation responses, studied with an electrical impedence aggregometer, were equivalent to those more laboriously obtained using platelet-rich plasma prepared by unit gravity sedimentation, studied with an optical light transmittance aggregometer. Platelet aggregation responses were normal with ADP or collagen stimulation, and absent with Ristocetin or bovine plasma stimulation. (2) Whole blood radioimmunoassay of platelet glycoprotein (GP) expression was performed using iodinated murine monoclonal antibodies HP1-1D (anti-GP IIb/IIIa) and 6D1 (anti-GPlb, kindly supplied by Dr. Barry Coller, Stony Brook, NY). After incubation with citrated whole blood, centrifugation was used to separate cell-bound antibody which was quantitated with a gamma counter. The patient’s whole blood had a normal level of cell-bound GP Ilb/IIIa, but a markedly reduced level of cell-bound GP lb (5% of normal mean; n = 20). (3) Whole blood smear immunocytochemical staining with the monoclonals (indirect immuno-alkaline phosphatase technique), and qualitative analysis by light microscopy, revealed a marked reduction of GP lb expression by the patient’s giant platelets, whereas GP Ilb/IIIa expression was normal. This latter technique might be especially valuable as a screening technique when the patient is not directly available for laboratory study. Together with the patient’s life-long history of thrombocytopenia and moderate bleeding diathesis, and other laboratory observations including markedly prolonged bleeding times and reduced whole blood prothrombin consumption, these data established diagnosis of BSS. We conclude that these three relatively simple assays of platelets in whole blood should be of particular value in the laboratory differential diagnosis of patients with congenital thrombocytopenias and giant platelet syndromes.

A 39-year-old 75 kg man with Type I Glanzmann's thrombasthenia developed recurring severe therapy-refractory nosebleeds, associated with nasal septal deformity, synechial scarring, and previous radiotherapy. During a 21 month period he required 16 hospitalizations for treatment of severe epistaxis. At initial hospitalization it was observed that his epistaxis ceased shortly after transfusion of 10 bags (units) of plasma cryoprecipitate (cryo), although transfusion with HLA-matched apheresis platelets from 3 donors, and topical therapy (cautery, packing), had been ineffective. Serum anti-platelet antibodies were not detectable by indirect immunofluorescence. During 9 subsequent hospitalizations his epistaxis stopped promptly (usually within 1 hour) following cryo transfusion (10 or 20 bags), including 6 occasions when cryo was the only therapy. On 6 additional occasions his epistaxis did not stop following cryo transfusion, but did stop after subsequent platelet transfusions or topical therapy. Eventually he underwent nasal septal reconstructive surgery surgery, and severe epistaxis has not recurred. Hemostatic studies, before and after cryo transfusions on 5 occasions, did not show improvement of platelet aggregation defects nor of Ivy bleeding times, although occasionally the volume of blood emanating from bleeding time punctures appeared decreased following cryo transfusion. Platelet glycoprotein (GP) IIb/IIIa antigen was measured in aliquots of 10 of the pools of cryo received by the patient (representing 100 bags of total volume 2200 ml), using an immunoradiometric assay (Nichols et al, Blood 68:300a, 1986). On average, the transfused cryo pools contained GP IIb/IIIa equivalent to 1.1 x 108 platelets/ml (range 0.6-1.7 x 108/ml. Our recently reported studies of blood bank cryo documented similar GP IIb/IIIa levels, and revealed that >93% of GP IIb/IIIa in cryo is present in the form of sedimentable membranous platelet macroparticles and microparticles. We hypothesize that the GPIIb/IIla-bearing platelet particles in transfused cryo might account for the improvement in hemostasis we frequently observed. We conclude that cryo transfusion deserves further study as a potentially useful therapeutic adjunct in promoting hemostasis in individuals with Glanzmann's thrombasthenia.