Platelet survival and turnover: important factors in predicting response to splenectomy in immune thrombocytopenic purpura

Autologous indium-111 platelet sequestration and survival studies were performed on 59 immune thrombocytopenic purpura (ITP) patients, 21 of whom underwent splenectomy shortly thereafter. Sequestration patterns were primarily splenic in 46 patients, primarily hepatic in 6 patients, and both splenic and hepatic in 8 patients. The mean platelet survival ranged from 15 to 211 hr (normal, 180-220 hr), and mean platelet turnover (a measure of platelet production rate) varied from 99 platelets/microliters/hr to 7,585 platelets/microliters/hr (normal 1,200-1,600 platelets/microliters/hr). Among splenectomy patients, 13 had an excellent response, and 8 had a fair or poor response. Neither the pattern of platelet sequestration nor the quantity of platelet-associated IgG was useful in predicting response to splenectomy. There was, however, a striking correlation between platelet studies showing short survival/high turnover and subsequent excellent response to splenectomy. Conversely, patients with only moderately decreased survival and low turnover had an unpredictable response to splenectomy. This investigation demonstrates that ITP patients are a heterogeneous population and include a significant subset whose thrombocytopenia results primarily from decreased turnover. Platelet kinetic studies appear useful in predicting beneficial response to splenectomy.     

Lymphocytotoxic antibody is a predictor of response to random donor platelet transfusion

The transfusion records of 189 patients with acute leukemia were analyzed to correlate lymphocytotoxic antibody (LCTAb) levels with response to a series of random-donor platelet transfusions (Tx). Twenty-one patients were studied twice at times of different LCTAb levels. All transfusions were given when patients were clinically stable without disseminated intravascular coagulation, bleeding, temperature > 101°F, or splenomegaly. The mean 1-hr and 24-hr corrected count increments (CCI) for all patients with negative LCTAb were 16,100 and 12,000, and values for patients with positive LCTAb were 5,600 and 2,600 (P < 0.0005). Thirteen patients had intermediate LCTAb (10–20%) and a variable response to Tx. Of the 137 patients with negative LCTAb levels 106 (77%) had good mean CCI of > 10,000 at 1 hr and > 7,500 at 24 hr following transfusion. In contrast of 60 patients with positive LCTAb (> 20% cytotoxicity), 53 (88%) had poor CCI of < 10,000 at 1 hr and < 7,500 at 24 hr after transfusion. Only 4 patients with positive LCTAb had a good response to random donor platelets at both 1 and 24 hrs. Eighteen patients had negative LCTAb with a high 1-hr and low 24-hr CCI. Thirteen of these had a history of positive LCTAb and in 9 there was an anamnestic rise following transfusion. Nine of 137 patients had negative LCTAb with low 1-hr and 24-hr CCI. LCTAb is highly predictive of response to random donor platelets. Cytotoxicity to > 20% of tested lymphocytes virtually precludes a good CCI at 1 and 24 hr.     

Failure of ticlopidine to inhibit deposition of indium-111-labeled platelets on Dacron prosthetic surfaces in humans

In a randomized double-blind trial we sought to determine whether short-term therapy with ticlopidine (250 mg bid for 14 days) inhibited platelet deposition on Dacron aortic bifurcation grafts that had been in place a year or longer. A total of 10 men, 42 to 69 years old, underwent indium-111 platelet imaging during both placebo and drug phases of the trial at 24, 48, and 72 hr after the injection of labeled platelets. Platelet accumulation was quantitated by a graft/blood ratio that compared background-corrected activity of indium-111-labeled platelets in the graft with whole-blood activity of indium-111-labeled platelets. Additionally, blinded qualitative visual analysis of the unprocessed images was used to compare graft area activity with activity in adjacent native arteries. Ticlopidine significantly prolonged the template bleeding time from 5.3 +/- 0.5 to 17.1 +/- 3.1 min (+/- SEM) (p = .003). However, by quantitative analysis there was no significant reduction in platelet deposition in the graft during ticlopidine therapy compared with placebo at 24 hr (graft/blood ratio 2.3 +/- 0.4 vs 2.6 +/- 0.3), 48 hr (3.1 +/- 0.5 vs 3.2 +/- 0.4), or 72 hr (3.9 +/- 0.7 vs 4.0 +/- 0.6) after injection of labeled platelets. By visual analysis, nine patients had positive results for abnormal platelet deposition when on placebo that were unchanged when on ticlopidine. The tenth patient had an equivocal result for abnormal platelet deposition when on placebo and a negative result for abnormal platelet deposition when on ticlopidine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Platelet density in essential thrombocythemia and polycythemia vera

This study aims to compare platelet density in myeloproliferative disorders (essential thrombocythemia (ET) and polycythemia vera (PV)) with platelet density of healthy subjects. Platelet density peaks were determined using a specially designed apparatus for scanning light transmission variations along test tubes containing density-separated platelets. Eighteen patients with myeloproliferative disorders (nine ET and nine PV) were compared with a control group consisting of 12 healthy volunteers. Compared with healthy volunteers, patients with myeloproliferative disorders had significantly lower platelet peak density ( P< 0.001). It is concluded that determination of peak platelet density may be a useful tool for excluding ET and PV. A high platelet density peak makes a clonal disorder less likely and a low density peak would confirm the suspicion.     

Platelet transfusion therapy in acute leukemia: lack of effect of splenomegaly on transfusion requirements and risk of hemorrhage

Platelet transfusions are an important supportive measure during treatment for acute nonlymphocytic leukemia (ANLL). The presence of splenomegaly may produce decreased posttransfusion platelet increments leading some to recommend an increased dose of platelets per transfusion in this situation. Forty-nine newly diagnosed patients with ANLL were evaluated during 1980 and 1981, and 24% had palpable splenomegaly. Although treated with usual doses of platelets per transfusion, there was no detectable statistical increase in transfusion requirement or incidence of hemorrhage in patients with splenomegaly. Experimental evidence indicates that the splenic platelet pool enlarges with splenomegaly, but the life span of circulating platelets is not significantly changed. Furthermore, the splenic platelet pool is in dynamic equilibrium with the circulating platelet pool thus allowing these platelets to participate in hemostasis. Although posttransfusion increment in platelet count may be less, it appears that platelet transfusion therapy need not be altered solely because of splenomegaly.     

A pilot trial of complement inhibition using eculizumab to overcome platelet transfusion refractoriness in human leukocyte antigen allo-immunized patients

Heavily transfused patients frequently develop human leukocyte antigen (HLA) allo-immunization resulting in platelet transfusion refractoriness and a high risk for life-threatening thrombocytopenia. Data suggest complement activation leading to the destruction of platelets bound by HLA allo-antibodies may play a pathophysiologic role in platelet refractoriness. Here we conducted a pilot trial to investigate the use of eculizumab, a monoclonal antibody that binds and inhibits C5 complement, to treat platelet transfusion refractoriness in allo-immunized patients with severe thrombocytopenia. A single eculizumab infusion was administered to 10 eligible patients, with four (40%) patients overcoming platelet refractories assessed measuring the corrected platelet count increment (CCI) 10–60 min and 18–24 h post transfusion. Responding patients had a reduction in the requirement for subsequent platelet transfusions and had higher post-transfusion platelet increments for 14 days following eculizumab administration. Remarkably, three of the four responders met CCI criteria for response despite receiving HLA-incompatible platelets. Our results suggest that eculizumab has the ability to overcome platelet transfusion refractoriness in patients with broad HLA allo-immunization. This study establishes proof of principle that complement inhibition can treat platelet transfusion refractoriness, laying the foundation for a large multicentre trial to assess the overall efficacy of this approach (ClinicalTrials.gov, identifier: NCT02298933).     

Novel methodology for assessment of prophylactic platelet transfusion therapy by measuring increased thrombus formation and thrombin generation

Currently, patients developing severe thrombocytopenia during chemotherapy treatment are prophylactically transfused with platelets. We developed two platelet function tests to report the improved haemostasis in the transfused patients, which were capable of detecting aberrant responsiveness of the platelets after transfusion. First, in a whole-blood flow test, platelet adhesion and thrombus formation were determined under high-shear flow conditions. Second, the procoagulant function of platelets was assayed in platelet-rich plasma by measurement of thrombin generation. Experimental conditions were established, where flow-induced adhesion and thrombin generation test parameters increased semi-linearly with the platelet concentration, and informed on the activation properties of platelets. The transfusion effects were evaluated for 38 thrombocytopenic patients, who were transfused with platelets stored in plasma or in synthetic medium (platelet additive solution II). In most but not all patients, transfusion resulted in increased adhesion and thrombus formation, as well as in improved platelet-dependent coagulation. Taken together, the increase in platelet count after transfusion explained 57% of the overall improvement in platelet function. In acute graft-versus-host disease, thrombus formation was normal, while platelet-dependent coagulation was higher than expected. We conclude that assessment of flow-induced adhesion and thrombin generation in acquired thrombocytopenia adequately determines the improved haemostatic activity by transfused platelets.     

Random donor platelet crossmatching: comparison of four platelet antibody detection methods

The standard lymphocytotoxicity assay (LCT), a biotin-avidin enzyme immunoassay (ELISA), platelet suspension immunofluorescence test (PSIFT), and platelet radioactive antiglobulin test (PRAT) were examined in prospective crossmatching for selection of compatible random donor platelets for refractory patients. One hundred seven episodes of pooled random donor platelet transfusions were evaluated in 26 patients. There was good reproducibility of results by individual techniques. Concordance of results by the different methods was 40-60%. One-hour and 24 hr posttransfusion corrected count increments (CCI) were compared as parameters for assessing success or failure of the transfusion. Using a rank scoring system, the relative efficiency of predictiveness for all transfusions was PRAT greater than LCT greater than PSIFT greater than ELISA. Combination of PRAT and LCT afforded the best predictability and sensitivity was higher than for either PRAT or LCT alone (93 vs. 79 and 62%, respectively). Mean posttransfusion CCI (x 10(9)/L) following PRAT-compatible platelets was 13.9 +/- 12.7 at 1 hr and 7.3 +/- 6.9 at 24 hr; following PRAT-incompatible platelets, 5.7 +/- 7.8 (1 hr) and 2.1 +/- 4.1 (24 hr). Results were similar for LCT-tested platelets. A radioimmunofiltration modification of the PRAT developed and used in selected cases was simple, fast, efficient, and inexpensive. The study indicated that the techniques evaluated are practical and feasible for routine use in the provision of compatible random donor platelets to the refractory patient who has no other cause for increased platelet destruction.     

Kinetics of indium-111-labelled platelets in HIV-infected patients with and without associated thrombocytopaenia.

Seven to 12% of HIV-infected patients have thrombocytopaenia. The pathophysiology of the thrombocytopaenia is not clear. It has been variously suggested that it may be caused by an increased peripheral platelet destruction, a defect in platelet production, or by a combination of these. The aim of the study was to elucidate the pathogenesis of HIV-associated thrombocytopaenia. We determined the mean platelet life span (MPLS) and calculated the turnover of autologous indium-111-labelled platelets in 17 HIV-positive patients, seven with thrombocytopaenia. The sites of sequestration of labelled platelets were quantified. The thrombocytopaenic patients had a very short MPLS (3.0+/-3.8 h) and a marked increase in platelet production (18.2+/-12.6x10(9)/l/h). The majority of these patients (5 of 7) had excessive sequestration of platelets in the spleen. Five of the patients with a normal blood platelet count had a shortened MPLS (109+/-23 h) and increased platelet turnover (3.8+/-1.2x10(9)/l/h), i.e. the increased peripheral platelet destruction was compensated for by increased platelet production. The other five patients with a normal platelet count had normal MPLS (195+/-11 h) and slightly increased platelet production (2.5+/-0.6x10(9)/l/h). We conclude that patients with HIV-associated thrombocytopaenia have increased peripheral platelet destruction. Platelet production is elevated but is insufficient to maintain a normal peripheral platelet count. In these patients platelets are predominantly sequestrated in the spleen. Patients with HIV infection and a normal blood platelet count may also have increased platelet production. This may be an early subclinical phase in the development of full-blown HIV-associated thrombocytopaenia.     

Simple,rapid, and automated method for detection of hyperaggregability of platelets using a hematology analyzer

Estimation of hyperaggregability of platelets is important for diagnosis and prevention of vascular events. We have developed and evaluated a simple and rapid method for detection of a hyperaggregable state of platelets by using an Abbott CELL-DYN(R) 4000 hematology analyzer. Citrated blood samples were collected from 62 patients with chronic cerebral infarction (CCI), of whom 19 patients were treated with ticlopidine, and from 9 healthy subjects. Platelet clumps were detected in the scatter plots for white blood cell populations with the hematology analyzer. Platelet clumps were positive in 20 of 43 (46.5%) CCI patients who were not treated with anti-platelet agents but not at all in 9 healthy subjects and in 19 CCI patients treated with ticlopidine. The detection of platelet clumps in citrated blood by the hematology analyzer was proved useful in detecting a platelet hyperaggregability in CCI patients. This method is simple, rapid, and automated and thus should be suitable for routine clinical use for monitoring indications and the efficacy of anti-platelet drugs.     

Platelet transfusion improves clot formation and platelet function in severely thrombocytopenic haematology patients

Prophylactic platelet (PLT) transfusion is a common practice in severely thrombocytopenic patients that reduces mortality, but responses to platelet transfusions are variable and difficult to predict in individual patients. In this prospective study, we evaluated the outcome of PLT transfusions in 40 patients with haematological malignancies, linking corrected count increment (CCI) to clot formation and agonist-induced platelet activation after transfusion. The CCI was highly variable between patients and 34% showed no response (1-h CCI < 7,5). Short time since the last PLT transfusion and extended storage time of the PLT product were linked to poor transfusion response, while patient sex, C-reactive protein or the number of chemotherapy cycles prior to transfusion did not influence transfusion outcome. High CCI and good PLT responsiveness to agonist stimulation predicted efficient clot formation in rotational thromboelastometry, but transfusion did not restore poor PLT function in patients to the level of healthy controls. Our study provides new insights into factors affecting PLT transfusion outcome in haematology patients with severe thrombocytopenia, and suggests that the thrombocytopenic environment, or disease-associated factors, may hamper platelet responsiveness.     

Evaluation of platelet function in thrombocytopenia

Whole blood aggregometry is a functional assay for determination of platelet function. Until now, whole blood aggregometry has not been considered feasible at low platelet counts. Hence, the objectives of the present study were to explore platelet function in thrombocytopenia using a novel index of impedance aggregometry adjusted for platelet count and evaluate the association to platelet function assessed by flow cytometry. Hirudin anticoagulated blood was collected from 20 healthy volunteers, 20 patients with primary immune thrombocytopenia (ITP), and 17 hematological cancer patients. Platelet function was analyzed by impedance aggregometry and by flow cytometry. Collagen, adenosine diphosphate, thrombin receptor agonist peptide-6, and ristocetin were used as agonists for both analyses. Thrombocytopenia in healthy whole blood was induced in vitro employing a recently published method. Platelet aggregation of thrombocytopenic patients was evaluated relative to the aggregation of healthy volunteers at the same platelet count. In flow cytometry, platelet function was described as expression of the platelet surface glycoproteins: bound fibrinogen, CD63, and P-selectin. Similar platelet counts were obtained in the patient groups (p = 0.69) (range: 13–129 × 10⁹/l). Aggregation adjusted for platelet count was significantly increased in ITP patients compared to healthy platelets across all agonists. The platelet aggregation was high in the 95% prediction interval, with 18 ITP patients above the prediction interval in at least two agonists. In contrast, the platelet aggregation was low in the prediction interval in cancer patients, and three cancer patients with platelet aggregation below the prediction interval in at least one agonist. ITP patients displayed increased expression of bound fibrinogen and CD63 following activation, compared with particularly cancer patients, but also compared with healthy platelets. This study demonstrated the feasibility of a novel approach to perform platelet function analyses in thrombocytopenia using impedance aggregometry adjusted for platelet count.     

The role of ABO matching in platelet transfusion

Abstract: A prospective controlled trial was performed to determine whether the use of ABO-identical platelets from the start of treatment might provide higher post-transfusion platelet increments, reduce the number of platelet transfusions and ultimately delay the onset of refractoriness. Forty newly diagnosed patients with haematological diseases were randomized to receive either pooled ABO-identical platelets or pooled platelets unmatched for ABO group throughout their course. The corrected platelet count increments (CCI) were calculated for the first 25 transfusions of each patient and non-immune factors present at the time of each platelet transfusion were documented. The mean CCI for the first 25 transfusions in the ABO-identical group was significantly higher (6600 ±: 7900 SD) than that achieved with ABO unmatched platelets (5200 ±: 7900; p<0.01). The effect was most marked for the first 10 transfusions for each patient where the CCI was 64% higher in the ABO-identical group (8200 ±: 7500 vs 5000 ±: 8100; p<0.0002). Patients given ABO-identical platelets required only about half as many transfusions in the first 30 days (10 versus 17, p<0.05) or during the first admission (11 versus 21 p<0.01) as patients in the ABO-unmatched group. A smaller percentage of patients in the ABO-identical group became refractory (36% vs 75% p<0.03). The data suggest that patients requiring long-term platelet support should be transfused with ABO-identical platelets.     

Preparation of Leucocyte-Poor Platelet Concentrates from Buffy Coats

To study survival and function of leukocyte-poor platelet concentrates (lp-PC) prepared from buffy coats, random platelet transfusions requested for thrombocytopenic patients were evaluated. The lp-PC issued were stored at 22 degrees C for either 1, 3 or 5 days before transfusion. From 31 transfusions, posttransfusion corrected count increments (CCI), corrected for body surface (m2) and divided by number of platelets transfused (1011), were calculated. The mean +/- SEM of the 1-, 24- and 48- hour CCI was 12.2 +/- 0.45, 11.2 +/- 0.51 and 8.8 +/- 0.58, respectively. No significant differences in CCI 24 h after transfusion were observed for 1p-PC stored for 1, 3 or 5 days. Hemostatic activity was observed in all 9 evaluable patients. It is concluded that platelets from 1p-PC survive well in patients, regardless of storage for 1, 3 or 5 days and that the platelets are hemostatically active after transfusion.     

A randomized study of buffy coat platelets in platelet additive solution stored 1–5 versus 6–7 days prior to prophylactic transfusion of allogeneic haematopoietic progenitor cell transplant recipients

Background and Objective  Storage of platelets > 5 days provides improved availability, logistical management and decreased outdating. Promising results on in vitro parameters and on in vivo post-transfusion recovery and survival of autologous platelets in healthy volunteers have earlier been shown. To provide additional verification, randomized patient transfusion studies are needed.
Materials and Methods  Sixty allogeneic haematopoietic progenitor cell transplant recipients were randomized to receive buffy-coat (BC) platelets stored in platelet additive solution (PAS) for 1–5 days the first time a prophylactic transfusion was needed after transplantation, followed the second time by platelets stored for 6–7 days or vice versa. The corrected count increment (CCI) for 1 and 24 h were calculated.
Results  CCI 1 h and CCI 24 h were higher for platelets stored 1–5 days as compared to 6–7 days, 10·4 ± 5·1 vs. 7·4 ± 3·8 ( P <  0·001) and 5·4 ± 4·1 vs. 2·6 ± 2·6 ( P <  0·001), respectively. Time to next platelet transfusion was significantly longer after a transfusion of platelets stored for 1–5 days as compared to platelets stored for 6–7 days: 2·2 ± 1·1 vs. 1·6 ± 0·8 days, respectively ( P <  0·005). No differences in bleeding events and no transfusion reaction were recorded.
Conclusion  The advantage of an extension of platelet storage time beyond day 5 should be balanced against the increased need for platelet transfusions that may occur and the conceivable risk of transfusion failure.     

肾综合征出血热患者血小板输注效果调查分析

目的:调查分析肾综合征出血热(HFRS)患者血小板输注效果。方法:根据血小板输注次数将70例116次输注血小板的HFRS患者分为3组,进行输注前及输注后24h外周血血小板计数,计算输注后血小板增加校正指数(CCI),进行血小板输注效果评价。结果:3组患者输注有效率比较差异有统计学意义(P0.05),以1次组有效率最高,其次为2次组,3次组有效率最低,平均有效率为37.93%。结论:HFRS患者血小板输注效果较差,且输注有效率随输注次数的增加而下降。     

P-Selectin expression, platelet aggregates, and platelet-derived microparticle formation are increased in peripheral arterial disease.

Platelet volume has been reported to be increased in vascular disease. Therefore, we studied the relationship of mean platelet volume and platelet count as well as flow cytometrically measured platelet size and platelet function in 50 patients with peripheral arterial disease and 50 healthy volunteers. Platelet activation was measured by P-selectin expression analysis on resting and on stimulated platelets, and the determination of platelet aggregates and platelet-derived microparticles using flow cytometry. P-Selectin expression on platelets was significantly elevated in patients suffering from peripheral arterial disease (all P<0.0001). Platelet aggregates (P<0.0001) and platelet-derived microparticles (P<0.0001) were significantly higher in the patient group compared with controls, whereas mean platelet volume and platelet count showed no significant differences. Platelet count was inversely related to mean platelet volume in patients and controls (r = -0.43, P<0.001). The present study supports the hypothesis of platelet hyperreactivity and circulating activated platelets in peripheral arterial disease. Mean platelet volume, and platelet count cannot be used as predictive markers for platelet activation in peripheral arterial disease patients.     

The interaction between preoperative platelet count and function and its relationship with postoperative bleeding in cardiac surgery

Platelet function tests (PFTs) before cardiac surgery are predictive of postoperative bleeding and can guide a correct timing of surgery in patients under P₂Y₁₂ inhibitors. Thrombocytopenia affects PFT and may determine postoperative bleeding. The present study aims to investigate the relationship between platelet count and function, and its role in determining postoperative bleeding in cardiac surgery patients pre-treated with P₂Y₁₂ inhibitors. The study includes 589 consecutive cardiac surgery patients, tested before surgery with platelet count and multiple electrode aggregometry (MEA) ADPtest (investigating P₂Y₁₂ receptor platelet reactivity) and TRAPtest (investigating the thrombin-dependent platelet reactivity). Platelet function was linearly associated (P = 0.001) with platelet count at the ADPtest and the TRAPtest, demonstrating a positive association in the whole spectrum of platelet count. The ADPtest (P = 0.001) and platelet count (P = 0.001) were negatively associated with postoperative bleeding, whereas the TRAPtest was not. At a multivariable analysis, the ADPtest (P = 0.026) and platelet count (P = 0.006) remained independent predictors of postoperative bleeding. The platelet transfusion rate was 5.7% in patients with ADPtest ≥30 U and platelet count ≥150 000 cells/µL, 14.3% in patients with ADPtest ≥30 U and platelet count <150 000 cells/µL, 38.9% in patients with ADPtest <30 U and platelet count ≥150 000 cells/µL, and 50% in patients with ADPtest <30 U and platelet count <150 000 cells/µL (P = 0.001).

Platelet function at MEA is dependent on the platelet count not only in the case of thrombocytopenia, but also in the whole range of platelet count; preoperative platelet count and function are determinants of postoperative bleeding, with a larger effect on platelet transfusions attributable to a poor P₂Y₁₂-dependent platelet function.     

The use of radiolabeled and fluorescein-labeled antiglobulins in assays to predict platelet transfusion outcome

We used both radiolabeled and fluorescein-labeled antiglobulins in assays to detect antibodies against platelets in multiply transfused patients to determine the value of these tests in predicting the outcome of platelet transfusion in such patients. In 15 allosensitized patients, we studied 68 single-donor platelet transfusions, 43 (63%) of which had a poor outcome, defined as a corrected count increment (CCI), less than 10,000. The results obtained with either test were significantly correlated with the CCI following transfusion (p less than 0.001), but the assay using the radiolabeled antiglobulin had slightly better sensitivity, specificity, and predictive value. When the assays were used in combination, there was again significant correlation with the CCI of the transfusion, p less than 0.001. When both assays predicted failure of the transfusions, 31/31 (100%) such transfusions resulted in a CCI of less than 10,000, and when both assays predicted success of the transfusions, 14/15 (93%) such transfusions resulted in a CCI of greater than 10,000. Both assays are useful in predicting the outcome of the platelet transfusions; when the assay results were concordant, almost total predictive accuracy was obtained.     

Enhanced circulatory parameters of human platelets cryopreserved with second-messenger effectors: an in vivo study of 16 volunteer platelet donors

Platelet transfusion represents an important component of the therapy for thrombocytopenic patients. Prolonged storage capabilities for platelets would alleviate many problems associated with blood banking. Unfortunately, current cryopreservation methods are complex to implement and result in loss of cell number and functional activity. Previous in vitro studies have shown that the use of ThromboSolTM, a platelet-stabilizing formulation, in the cryopreservation of platelets results in significant retention of cell number and in vitro functional activities in addition to reducing the DMSO requirement to only 2%. We evaluated the in vivo circulatory parameters of platelets cryopreserved with ThromboSol. Single donor platelet units were obtained from healthy volunteers (n = 16); the units were then split and cryopreserved with either ThromboSol and 2% DMSO or 6% DMSO alone. Following storage at -80 degrees C for 7-10 d the samples were thawed, washed and radiolabelled with either 51Cr or 111In. The paired samples were then mixed and reinfused into the autologous volunteer. At various time intervals following transfusion a blood sample was drawn and the quantity of circulating labelled platelets was determined. The percent recovery and survival time was determined by multiple-hit analysis. The ThromboSol-treated platelets, as compared to the 6% DMSO-treated platelets, displayed statistically higher percent recovery (40.2% v 28.8%) and survival time (166.3 h v 152.1 h). These results demonstrated that platelets cryopreserved with ThromboSol displayed superior in vitro and in vivo characteristics as compared to the standard 6% DMSO method. The use of ThromboSol allowed for a 3-fold reduction in the DMSO concentration in conjunction with a 40% increase in circulating cell number and normal survival times.