Transfusion Of Fresh Platelets Research Articles

Platelet Refractory Cases after Transfusion of Fresh and Stored Platelet in all Children

Introduction: Acute leukemia is the most common form of cancer in children, platelet transfusion is needed for the chemotherapy of acute lymphoblastic leukaemia children. Platelets are transfused for therapeutic and prophylactic purposes. Transfusion of stored platelet concentrates (up to 5 days) has been demonstrated to be as effective as transfusion of fresh platelet concentrates (upto 24 hours). Platelet refractory cases were also observed in this study that was detected by Corrected Count Increment (CCI) and Percent Platelet Recovery (PPI) at 1hour and 24 hours. Aim of the study: The aim of this study was to observe the platelet refractory cases after transfusion of fresh and stored platelet in acute lymphoblastic leukemia (ALL) in a tertiary care hospital, Dhaka. Methods: A cross-sectional study was conducted in the Department of Clinical Pathology, Paediatric Haematolo- Oncology and transfusion Medicine BSMMU, Department of Haematology and Paediatric Haemato-Oncology in Dhaka Medical College Hospital from March 2010 to February 2011 where 81 children diagnosed with acute lymphoblastic leukaemia were taken as the study population. Non probability purposive sampling was used by fulfilling the inclusion criteria. Ethical consideration was taken by the BSMMU ethical review committee. A data sheet with two parts (Part A and Part B) was designed with a view to collect data from the patients to be enrolled in the study. Data were analyzed using the SPSS version 25.0. Results: Out of 81 in 47 children with acute lymphoblastic leukemia (ALL), fresh platelet concentrates (FPC) (upto 24 hours) or day-0 platelets were transfused. In 34 children, stored platelet concentrates (SPC) (days 1–5) were transfused. In 27 cases, platelet concentrates were transfused both fresh and stored. In FPC and SPC, the corrected count increment at one hour (CCI 1h) was 20.5×109/L and 18.9×109/L respectively. FPC and SPC values for the mean corrected count increment at 24 hours (CCI 24h) were 15.5×109/L and 13.8×109/L respectively. Platelet refractory cases were 15(18.5%) out of 81 cases transfused. Platelet refractory cases were 7(15%) out of 47 cases transfused with FPC and 8(23%) out of 34 cases transfused with stored platelet concentrate (SPC). There were no significant differences (P<0.05) between FPC and SPC according to platelet refractoriness. Conclusion: In vivo quality of freshly generated platelet (upto 24 hours) versus stored platelet concentrates (up to 5 days) were determined after 1 hour and 24 hours. 1-5 day’s stored PRP-PCs are as effective as fresh PRP-PCs for sufficient platelet increment.

Effect of Chronic Alcoholism on Traumatic Intracranial Hemorrhage

Traumatic intracranial hemorrhage (TICH) is one of the commonest indications for neurosurgical consultation after trauma. Worsening neurologic examination results, size of initial TICH, presence of displaced skull fracture, and concomitant anticoagulant use at the time of injury drive the recommendations for repeat computed tomography of head (RCTH), to assess for stability of intracranial hemorrhage. Chronic alcohol use is not generally considered an indication for repeat head computed tomography (CT). A retrospective study of 423 patients with TICH with normal admission platelet (PLT) counts was reviewed for this study, taken as a subset of 1330 patients with TICH admitted to Lahey Hospital and Medical Center over a 3-year period. Of these 423 patients, 330 were classified as nonalcoholics and 93 were classified as alcoholics, based on whether alcohol use disorder was documented in the patient's medical record, present before injury. The normal PLT level was defined as ≥100,000 μ/L. Patients were excluded from review if they had comorbid conditions that could cause PLT dysfunction or coagulopathy. Continuous and categorical variables were compared using independent t test and χ2, respectively. Binary logistic regression was used to predict outcome: stable versus worsening of TICH on RCTH. Statistical analysis was conducted using SPSS version25. The mean age of the nonalcoholic and alcoholic cohorts were 71.9 years and 54.8 years, respectively. A significantly higher percentage of alcoholics were male. There was a statistically significant difference (χ2= 8.14; P < 0.004) in radiologic progression of TICH between the 2 groups, with the alcoholics having a worsening RCTH 16.1% of the time compared with only 6.7% in nonalcoholics. Chronic alcohol use was an independent predictor of radiologic progression in patients with normal PLT level (odds ratio, 2.69; confidence interval, 1.34-5.43; P < 0.006). Chronic alcohol use was an independent predictor of radiologic progression of TICH in the setting of normal PLT level. Modification of this risk of progression with transfusion of fresh PLTs in chronic alcoholic patients with TICH needs to be investigated in a prospective trial.

In vitro thromboelastometric evaluation of the efficacy of frozen platelet transfusion

BackgroundAlthough frozen platelets are extensively used in remote locations and military environments, scientific evidence of their efficacy is scarce. The objective of this study was to evaluate the in vitro hemostatic efficacy of frozen versus fresh platelet transfusions by rotational thromboelastometry (ROTEM) to ascertain whether the freezing and thawing process impaired platelet contribution to clot strength. MethodsAn experimental study was performed using platelet in vitro transfusions. Blood samples were collected from 12 patients with non-autoimmune thrombocytopenia. The samples were each transfused with one of 6 pairs of fresh platelet concentrates and platelet concentrates frozen with dimethylsulfoxyde. Optical platelet counts, coagulation studies and ROTEM (EXTEM and FIBTEM) were performed for the baseline and the post-transfusion samples. ResultsOnly fresh platelet transfusions significantly increased the EXTEM maximum clot firmness (MCF) and maximum clot elasticity (MCE) over baseline (p<0.001), achieving values within the normal range. The frozen platelet contribution to MCE was negligible. However, the EXTEM clotting time (CT) was significantly (p<0.001) shorter after the frozen platelet transfusion compared with the fresh platelet transfusion. The EXTEM clot formation time (CFT) was significantly shortened after the transfusion of fresh platelets (p=0.002). ConclusionThe ROTEM analysis assessment indicates a dual effect in frozen platelet transfusion: it produces a hypercoagulable state (shortening of CT), and a second, more predominant effect of frozen platelets’ functionality impairment compared with fresh platelets (shorter MCF/MCE and longer CFT).

Successful treatment of kasabach-merritt syndrome with vincristine and surgery: a case report and review of literature

IntroductionHaemangiomas are vascular lesions resulting from abnormal proliferation of blood vessels. They are the most common pediatric neoplasm. Kasabach-Merritt syndrome is a rare type of vascular lesion with peculiar characteristics. The diagnosis is based upon three basic findings; enlarging haemangioma, thrombocytopenia and consumption coagulopathy.Case presentationA 5 month old boy was admitted to the Pediatrics department for the management of an abdominal wall mass. He was the first child of consanguineous parents, born in a private hospital following uncomplicated pregnancy and delivery. At birth a bluish birth mark 5 cm × 5 cm was noted below the umbilicus. Over the next five months, this birth mark increased in size and evolved into a swelling. As a result, the patient was admitted to Maternal and Child Health (MCH) unit for the management of this swelling.The clinical findings and imagining studies followed by laboratory investigations strongly suggested the diagnosis of Kasabach-Merritt syndrome.Vincristine was initiated after a trial of corticosteroids when the platelet count was 6000/cmm. One week after the start of vincristine the size of the lesion started to decrease. At the end of 6th week the lesion size decreased to half and the platelet count increased to 49,000/cmm. Vincristine was continued for another 2 weeks, no further improvement in lesion size or platelet count was observed. Vincristine was discontinued and the patient was shifted to the paediatric surgery department. A fresh platelet transfusion was given and the haemangioma was excised completely.The histopathological examination of the excised mass revealed a caverno-capillary haemangioma with infiltration into skeletal muscles.ConclusionSix weeks treatment with vincristine in a dose of 0.5 mg/kg/week followed by surgical excision may be the best management in selected cases of Kasabach-Merritt syndrome.

In Vivo Evaluation of Extended Stored Platelet Concentrates.

Background: With the introduction of bacterial testing, extended storage of platelets is now possible as long as platelet viability is maintained. Although apheresis platelets have recently been licensed for seven days of storage, platelet concentrates are still only licensed for five days. We performed studies to determine the post-storage viability of platelets stored as concentrates. As yet, there are no established criteria for platelet viability that must be met at the end of storage. However, two different criteria for evaluating post-storage platelet viability have been suggested:compare the stored platelet results with each donor's fresh platelet results; orestablish a fixed platelet standard with an expected mean value along with the lower limit of the 95% confidence interval (lower 95% CI) of the mean.Methods: Forty-four normal volunteers donated a unit of whole blood, the whole blood was centrifuged to give platelet-rich plasma (PRP), and the PRP was then centrifuged to produce a platelet concentrate. The platelet concentrates were re-suspended and stored in either 100% plasma or in 20% plasma and 80% Plasmalyte (a platelet storage solution) for five to eight days in Terumo Teruflex bags. At the end of storage, a sample of blood was obtained from each volunteer to prepare fresh platelets to compare the results of a fresh platelet transfusion with the transfusion of the same volunteer's stored platelets. The fresh and stored platelets were alternately radiolabeled with either 51Cr or 111In, re-injected into their volunteer donor, and serial blood samples were drawn from the volunteer after transfusion of the fresh and stored platelets to determine platelet recoveries and survivals.Results: Results are shown in Table 1.Conclusions: After seven days of storage in plasma, the platelets could qualify for standards of:74% and 53% as a simple ratio of fresh to stored platelet recoveries and survivals, respectively;according to Dumont's method of analysis (Transfusion, in press), achievable stored platelet recoveries would be 63% of fresh and survivals would be 40% of fresh; andas a fixed standard, platelet recoveries averaged 45% and survivals 4.4 days with lower 95% CI's of 35% and 3.3 days, respectively.After eight days of storage in plasma, platelet recoveries and survivals gave unacceptable results. Instead of increasing or at least maintaining post-storage platelet viability, Plasmalyte markedly reduced platelet viability compared to plasma stored platelets at each storage interval.In Vivo Radiolabeled Autologous Platelet Recoveries and SurvivalsSTORAGE CONDITIONSPLATELET RECOVERIES (%)PLATELET SURVIVALS (Days)SolutionTime (Days)NFreshStoredFreshStoredPlasma51062±1255±117.7±1.56.1±1.0Plasma61061±746±128.2±1.55.1±1.6Plasmalyte6347±3029±165.1±3.41.8±0.2Plasma71061±1145±148.3±1.04.4±1.5Plasmalyte7562±1730±127.4±0.62.2±1.1Plasma8367±1231±88.3±0.62.9±0.8Plasmalyte8370±321±88.2±0.80.7±0.1Data are given as the average ±1 S.D.

Hemostatic Properties of Infusible Trehalose-Stabilized Lyophilized Platelet Derivatives.

Availability of platelet concentrates for treatment of bleeding associated with thrombocytopenia, trauma, or drug-induced coagulopathies is problematic due to the short 5 day platelet storage time and because platelets require controlled shaking at ambient temperature in order to remain viable, a condition which augments bacterial growth. To address the platelet availability problem we expanded upon trehalose cryo-preservation technology to create a lyophilized hemostatic platelet derivative. Washed platelets were stabilized by accumulation of 5–10 mM intracellular trehalose via fluid phase endocytosis then formulated with excipients and lyophilized. Lyophilized platelets were instantaneously rehydrated with > 90% recovery and were stable for at least 3–6 months at ambient temperatures. Rehydrated (RH) platelets responded quantitatively to α-and γ-thrombin and ristocetin by transmittance aggregometry and were partially agglutinated by collagen as judged by aggregometry and single cell counting using the Platelet Works® system. RH platelets co-aggregated in a dose dependent manner when mixed with fresh autologous platelets during collagen-induced activation. Aggregation response to low-dose thrombin and collagen was inhibited by the GPIIb/IIIa antagonist RGDS and by EGTA. RH platelets were quantitatively incorporated into fibrin clots and elicited platelet-dependent fibrin-clot retraction ~ 60% as well as fresh platelets. RH platelets were similar in size to fresh and had less than 25% submicron particles as judged by electronic particle counting and flow cytometry scatter profiles. RH platelets were partially activated upon rehydration as judged by anti P-selectin and anti-LAMP-3 binding, yet GPIIb/IIIa remained in a resting conformation, as judged by a lack of PAC-1 binding. GPIIb/IIIa receptors were present as judged by the binding of complex-dependent (clone 5B12) and function-blocking (clone P2) antibodies. RH platelets also contained intact GPIbα as judged by binding of the function-blocking MoAb AN51. Function of GPIIb/IIIa and collagen receptors on RH platelets was further demonstrated as RH platelets adhered to immobilized fibrinogen and collagen in the absence of added agonists and in a dose-dependent manner. Moreover, RH platelets exhibited a two-fold increase in platelet procoagulant activity in the presence of thrombin receptor agonist peptide SFLLRN as judged by Annexin-V binding. Procoagulant and hemostatic activity was further demonstrated as RH platelets accelerated the clotting of recalcified whole thrombocytopenic blood in a dose-dependent manner similarly to fresh platelets. Lastly, RH platelets corrected the coagulopathy induced by contact pathway inhibition with aprotinin during the recalcification of citrated whole blood. The technology has been scaled to single donor platelet aphaeresis units, equivalent to a standard transfusion dose. Preclinical animal models of safety, efficacy, and circulation persistence are currently being evaluated. In summary, trehalose- stabilized lyophilized platelet derivatives contain numerous in vitro hemostatic properties and may offer an attractive alternative to fresh platelet transfusions when the latter are indicated yet unavailable.

Effect of heparin reversal and fresh platelet transfusion on platelet emboli post-cardiopulmonary bypass in a pig model.

Heparin reversal by protamine and fresh platelet transfusion may decrease bleeding complications post-cardiopulmonary bypass (CPB) and may increase the level of organ trapped platelet emboli. Platelet emboli were quantified in two groups of 12 Yorkshire pigs (30-35 kg), where 111indium labeled autologous platelets (INPLT: 850-1,200 microCi) were injected intravenously before and after CPB (BCPB, ACPB), and the platelet emboli level in intact organs and their samples (brain, heart, kidneys, lung, liver, and spleen) was quantified with an ion chamber and a gamma counter, respectively. All pigs were systemically heparinized (ACT > 400 sec). CPB was carried out at 2.5-3.5 L/min at 28 degrees C using a centrifugal pump, an oxygenator (OX:Bentley Univox 1.8 m2), an arterial filter (AF:0.25 m2), and a cardiotomy reservoir (CR: BMR 250) for 90 min. Heparin was reversed with an equivalent dose of protamine. The percent of INPLT dose (ID%, mean +/- SD) in organs of BCPB and ACPB pigs was calculated. The sequence of platelet emboli on a unit weight basis (ID%/g) had the following order: Spleen > Liver > Lung > Kidneys > Heart > Brain. The presence of significantly higher levels of emboli in brain, heart, and kidneys in the ACPB than the BCPB group suggest that platelet transfusion after heparin reversal with protamine may increase the risk of platelet emboli. However, it is an acceptable risk for patients having bleeding complications post-CPB.

In-vitro platelet sensitivity to collagen-induced aggregation and in-vitro platelet deterioration rate during storage, are both inversely proportional to the in-vivo blood platelet concentration in normal individuals: preliminary documentation of these theoretically predictable relationships

This preliminary study documents two new functional relationships for platelets obtained from normal subjects, whose individual blood platelet concentrations (IBPCs) are in the normal range. Firstly, platelets from subjects (or donors) with high-normal IBPCs are the least sensitive to collagen-induced aggregation (a significant inverse correlation). This may be of importance in determining the likely efficacy of fresh platelet transfusions obtained from donors with different IBPCs within the normal range. Secondly, platelets from subjects/donors with high-normal IBPCs deteriorate less rapidly during storage (a significant inverse correlation), perhaps due to differences in platelet biochemical activity between individuals. Such measurements of platelet deterioration rate were based upon the development of a new experimental technique, in which sterile test-PRP was incubated at 37°C with continuous (quarter-hourly) indirect measurements of changes in platelet morphology. This tube-based method is described in detail. The functional relationships observed do have a theoretical basis within the work of others, which is appropriately outlined. Particular discussion pivots around the possibility of using the deterioration rate relationship to predict how therapeutic platelet concentrates prepared from a given donor of know IBPC, may retain their morphological integrity during routine blood bank storage.

Platelet storage for 7 days in second-generation blood bags.

Plastic storage bags designed to optimize O2 and CO2 transfer to preserve platelets for 7 days prior to transfusion were studied in vivo and in vitro. Platelets stored 7 days in second-generation CLX bags were compared to platelets stored 3 days in standard (CL-3861) 3-day storage bags and platelets transfused within 24 hours of collection. The CLX bags maintained concentrate pH at a mean of 6.85 +/- 0.03 (SEM) after 7 days, while in standard bags after 3 days of storage, the mean pH was 6.46 +/- 0.03. A smaller proportion of platelets stored 7 days in CLX bags were discarded because of a pH less than 6.0 compared to those stored 3 days in CL-3861 bags (10 vs 21%). Poststorage pH showed strong correlation with concentrate platelet count and weak correlation with concentrate white cell count in both bag types. There was no significant difference in the mean corrected platelet count increments between platelets stored 7 days in second generation CLX bags and those stored 3 days in CL-3861 bags (10,000 and 12,200 at 1 hour, and 7000 and 7500 at 24 hours, respectively) following transfusion to 16 thrombocytopenic recipients. However, transfusion of fresh platelets achieved mean corrected increments at both 1 and 24 hours posttransfusion that were higher than seen with either group of stored platelets (20,100 at 1 hour and 10,800 at 24 hours). Platelets can be stored 7 days in second-generation CLX blood bags with results comparable to those of platelets stored 3 days in standard bags.

Therapeutic effectiveness of frozen platelet concentrates for transfusion

Six patients received platelet concentrate transfusions from their HLA- identical siblings. Platelet concentrates were administered either fresh, or after being frozen in 10% dimethylsulfoxide, at a slow controlled rate (1 degree C/min) or rapidly (approximately 8 degrees C/min) in the vapor-phase of a liquid nitrogen refrigerator. The median freeze-thaw loss was 13.5%. The mean 1-hr and 20-hr corrected increments in platelet count were calculated for fresh platelet concentrates transfused before and after transfusion with controlled- rate frozen and vapor-phase frozen platelet concentrates. There was no significant difference among the first and second transfusion of fresh platelet concentrates, nor was the difference observed between fresh and controlled-rate frozen platelet concentrates significant. The difference between fresh and vapor-phase frozen platelet concentrates, and between controlled-rate frozen and vapor-phase frozen platelet concentrates were highly significant (p &lt; 0.01). In vitro tests of aggregation using ristocetin and platelet ultrastructural studies paralleled the transfusion experience. Our results indicate that HLA- identical platelet concentrates can be successfully frozen and thawed for transfusion if a slow, controlled rate of freezing is employed. The use of HLA-identical frozen platelet concentrates may be important in emergency situations for the refractory patient and potentially for the establishment of a platelet concentrate bank.

Therapeutic Effectiveness of Frozen Platelet Concentrates for Transfusion

Six patients received platelet concentrate transfusions from their HLA-identical siblings. Platelet concentrates were administered either fresh, or after being frozen in 10% dimethylsulfoxide, at a slow controlled rate (1 degree C/min) or rapidly (approximately 8 degrees C/min) in the vapor-phase of a liquid nitrogen refrigerator. The median freeze-thaw loss was 13.5%. The mean 1-hr and 20-hr corrected increments in platelet count were calculated for fresh platelet concentrates transfused before and after transfusion with controlled-rate frozen and vapor-phase frozen platelet concentrates. There was no significant difference among the first and second transfusion of fresh platelet concentrates, nor was the difference observed between fresh and controlled-rate frozen platelet concentrates significant. The difference between fresh and vapor-phase frozen platelet concentrates, and between controlled-rate frozen and vapor-phase frozen platelet concentrates were highly significant (p < 0.01). In vitro tests of aggregation using ristocetin and platelet ultrastructural studies paralleled the transfusion experience. Our results indicate that HLA-identical platelet concentrates can be successfully frozen and thawed for transfusion if a slow, controlled rate of freezing is employed. The use of HLA-identical frozen platelet concentrates may be important in emergency situations for the refractory patient and potentially for the establishment of a platelet concentrate bank.

Clinical Experience with Transfusion of Cryopreserved Platelets

Multiple units of platelet concentrate obtained by plateletpheresis of normal, 'random' or HL-A matched donors were pooled and frozen in polyolefin bags using 5% dimethysulphoxide (DMSO) as a cryoprotective agent and a controlled freezing rate of I degrees C/min. The platelets were stored at approximately-I20 degrees C for as long as 20I days, thawed rapidly at 37 degrees C, washed once and resuspended in ACD plasma prior to transfusion. Two different final concentrations of platelets (approximately 2.7 and 9.0 X 10(12)/1.) were studied. Twenty-three thrombocytopenic patients have received a total of 40 frozen platelet transfusions. The mean freeze-thaw loss was 2I% and was similar for both platelet concentrations. All transfusions were well tolerated and there were no side effects attributable to the small amounts of DMSO infused. Increments in platelet counts I h after transfusion ranged from 0 to 102 X 10(9)/1. with an overall mean corrected increase in evaluable patients of 12 800 (increase x surface area (m2)/number of platelets transfused x 10(11)). Corrected increases tended to be greater with the low concentration of platelets. Overall, the increase in count for the frozen platelet transfusions was 65% of the increments obtained with fresh platelet transfusions administered within 1 week of the frozen platelets. Bleeding times were partially corrected after four out of six transfusions with post-transfusion counts greater than 50 X 10(9)/1., and active haemorrhage was controlled in some patients by frozen platelet transfusions. These results indicate that pooled platelets can be frozen, thawed and transfused with reasonable efficiency. The frozen platelets can circulate and function haemostatically and may eventually play an important role in supportive care.

Platelet function in recipients of platelets from donors ingesting aspirin.

The effect of fresh platelet transfusions from donors ingesting aspirin was evaluated in a group of thrombocytopenic recipients. Prolonged bleeding times were corrected to normal in recipients of platelets from donors who had taken aspirin 36 hours before donation, but not in those receiving platelets from donors who had taken aspirin within 12 hours of donation. In healthy volunteers, the abnormalities induced by aspirin ingestion on the bleeding time and epinephrine-induced platelet aggregation disappeared by 72 hours after ingestion. Analysis of the data indicates that when approximately 20 per cent of the circulating platelets have not been exposed to aspirin, the hemostatic function of the platelet pool is maintained. Thus, widespread use of aspirin should not present a serious problem in the selection of platelet donors.

Transfusion of fresh platelet concentrates to adult patients with thrombocytopenia.

Fresh platelet concentrates were given to 18 adult patients on 68 occasions without adverse effect. The concentrates were prepared by means of a closed‐system plateletpheresis technic which permitted rapid and frequent bleeding of donors. There was a direct relationship of the amount of platelets infused to the mean posttransfusion increment. Excellent hemostatic effect was noted in 84% of patients with active bleeding when the platelet increment was 40,000/mm3 or better. Transfusion of large numbers of platelet concentrates is effective in controlling or averting bleeding in adults with thrombocytopenia and is recommended on a therapeutic and prophylactic basis.

Congenital bleeding disorders with long bleeding time and normal platelet count: I. Glanzmann's thrombasthenia (report of fifteen patients)

The clinicopathologic details of fifteen patients with thrombasthenia are reported. The bleeding tendency appeared early in life, with varying degrees of mucous and cutaneous bleeding. The diagnostic criteria, which are generally accepted, included normal platelet count, long bleeding time, deficient clot retraction and absent platelet aggregation. In twelve of the thirteen families inheritance was as an autosomal recessive trait; in the thirteenth it was possibly dominant. The only effective therapy remains transfusion of fresh platelets. The life span of radioactive autologous platelets in this sense was normal. Indirect evidence suggests that a platelet surface abnormality is involved. This abnormality could not be detected morphologically, although significant electron microscopic anomalies, including steatosis, abnormal granules and Golgi vesicles, were found. Significant glycolytic abnormalities were present in only one case, in contrast to the findings in previous studies [15, 16]. It appears that the defects in platelet adhesion and clot retraction may be more readily related to the deficient adsorption properties of these platelets than to a metabolic derangement. Platelet coagulant and lytic activities in the presence of kaolin were reduced. These deficiencies may be related to delayed or defective activation of plasmatic factors XII and IX and platelet factor 3. The inability of these platelets to aggregate with ADP may be fundamental to these anomalies. Although the release of aggregating activity occurs, the platelets remain unreactive to ADP and to most foreign surfaces, suggesting that there is a membrane defect of significance in the derangement of hemostasis.

Comparative effectiveness of fresh and lyophilized platelets in controlling irradiation hemorrhage in the rat.

The efficiency of fresh vs. lyophilized platelet transfusions to control radiation -induced hemorrhage were tested in rats by gross observation for bleeding, platelet count, hematocril, microscopical study of lymph node sections, and susceptibility to bleeding from minor trauma. Hemorrhage occurs in irradiated, untreatud rats around the fifth post irradiation day increasing with the progress of platelet fall, which reach a minimum around the tenth day. Fresh and lyophilized platelet transfusions were performed on 5th, 7th and 9th day. Whereas fresh platelet transfusions raised the platelet count to 2 to 3 times the normal and stopped hemorrhage lyophilized material had no effect on platelet counts which were not different from irradiated controls and did not show any infiuence on the bleeding tendency. In the lyophilized platelet transfused rnts, the hematocrit dropped more than in the irradinted controls. (auth)