Prediction of the effect of immunoglobulin therapy in ITP

Summary The correlation between the response to high-dose immunoglobulin therapy (IVIg) and the sequestration pattern of Indium-labeled platelets (In-PLT) in the body was studied in 9 patients with chronic idiopathic thrombocytopenic purpura (ITP). Patients that has prominent platelet sequestration in the spleen responded to IVIg. In these patients, splenic sequestration decreased by 20–30% after IVIg without significant changes in hepatic sequestration. This finding suggests that the blocking of splenic Fc receptors with immunoglobulin minimized the destruction of sensitized platelets. However, patients who had almost equal platelet sequestration in the liver and spleen did not respond to IVIg. In these patients, hepatic sequestration decreased after IVIg, whereas splenic sequestration increased. Thus, it appears that estimating the platelet sequestration pattern using In-PLT is useful for predicting the effects of IVIg.Presented at the International Workshop on ITP, August 26 and 27, 1988, Lucerne, Switzerland     

Does the site of platelet sequestration predict the response to splenectomy in adult patients with immune thrombocytopenic purpura?

Splenectomy is the only potentially curative treatment for chronic immune thrombocytopenic purpura (ITP) in adults. However, one-third of the patients relapse without predictive factors identified. We evaluate the predictive value of the site of platelet sequestration on the response to splenectomy in patients with ITP. Eighty-two consecutive patients with ITP treated by splenectomy between 1992 and 2013 were retrospectively reviewed. Platelet sequestration site was studied by ¹¹¹Indium-oxinate-labeled platelets in 93% of patients. Response to splenectomy was defined at last follow-up as: complete response (CR) for platelet count (PC) ≥100?×?10⁹/L, response (R) for PC≥30?×?10⁹/L and <100?×?10⁹/L with absence of bleeding, no response (NR) for PC<30?×?10³/L or significant bleeding. Laparoscopic splenectomy was performed in 81 patients (conversion rate of 16%), and open approach in one patient. Median follow-up was 57 months (range, 1–235). Platelet sequestration study was performed in 93% of patients: 50 patients (61%) exhibited splenic sequestration, 9 (11%) hepatic sequestration and 14 patients (17%) mixed sequestration. CR was obtained in 72% of patients, R in 25% and NR in 4% (two with splenic sequestration, one with hepatic sequestration). Preoperative PC, age at diagnosis, hepatic sequestration and male gender were significant for predicting CR in univariate analysis, but only age (HR?=?1.025 by one-year increase, 95% CI [1.004–1.047], p?=?0.020) and pre-operative PC (HR?=?0.112 for?>?100 versus <=100, 95% CI [0.025–0.493], p?=?0.004) were significant predictors of recurrence-free survival in multivariate analysis. Response to splenectomy was independent of the site of platelet sequestration in patients with ITP. Pre-operative platelet sequestration study in these patients cannot be recommended.     

Platelet turnover and kinetics in immune thrombocytopenic purpura: results with autologous 111In-labeled platelets and homologous 51Cr- labeled platelets differ

Mean platelet survival and turnover were simultaneously determined with autologous 111In-labeled platelets (111In-AP) and homologous 51Cr- labeled platelets (51Cr-HP) in ten patients with chronic immune thrombocytopenic purpura (ITP). In vivo redistribution of the 111In-AP was quantitated with a scintillation camera and computer-assisted image analysis. The patients were divided into two groups: those with splenic platelet sequestration (spleen-liver 111In activity ratio greater than 1.4), and those with diffuse sequestration in the reticuloendothelial system. The latter patients had more severe ITP reflected by pronounced thrombocytopenia, decreased platelet turnover, and prominent early hepatic platelet sequestration. Mean platelet life span estimated with 51Cr-HP was consistently shorter than that of 111In-AP. Platelet turnover determined with 51Cr-HP was thus over-estimated. The difference in results with the two isotope labels was apparently due to greater in vivo elution of 51Cr. Although the limitations of the techniques should be taken into account, these findings indicate that platelet turnover is not always normal or increased in ITP, but is low in severe disease. We suggest that this may be ascribed to damage to megakaryocytes by antiplatelet antibody. The physical characteristics in 111In clearly make this radionuclide superior to 51Cr for the study of platelet kinetics in ITP.     

The site of platelet destruction in thrombocytopenic purpura as a predictive index of the efficacy of splenectomy

The significance of the site of platelet sequestration in determining the indication for splenectomy in idiopathic thrombocytopenic purpura (ITP) is a controversial subject. However, most of the negative conclusions are based on 51chromium labelling of homologous platelets. We report here the results of an analysis of 222 cases in which the kinetic study of 111indium-oxinate-labelled autologous platelets was performed under homogeneous technical conditions. 103 of these patients subsequently underwent splenectomy. This study demonstrates that the site of platelet sequestration in active ITP constitutes a variable independent of the patient's age, history of the disease and its severity (platelet count, lifespan). The sequestration site is a good predictive element of the short-term efficacy of splenectomy (71/76 cases with splenic sequestration obtained a platelet count exceeding 100 x 10(9)/l versus 7/13 cases with mixed sequestration and 1/14 cases with hepatic sequestration), and the long-term results (6 months to 5 years after splenectomy) do confirm the clinical value of this study.     

Reevaluation of the prognostic factors for splenectomy in chronic idiopathic thrombocytopenic purpura (ITP): a report on 181 cases

From 1973 to 1986 we splenectomized 181 patients with chronic ITP after platelet kinetic studies with 51Cr or 111In. Mean age at diagnosis was 34 (range 4-79 yr). Follow-up of at least 1 yr after splenectomy was available in every patient. 141 patients (78%) achieved remission (platelets greater than 100 x 10(9)/l by 3 months after splenectomy), of whom 9 subsequently relapsed. Among the 40 non-responders at 3 months, 3 achieved a later remission spontaneously. Factors associated with response to splenectomy included a high post-operative platelet count (p = 0.0001), younger age at the time of surgery (p = 0.0077) and predominantly splenic sequestration of platelets (p = 0.0002), the two latter factors being partially correlated. In a multivariate analysis, however, only post-operative platelet count and age retained an independent prognostic significance, whereas the sequestration site of platelets had only borderline value. These results are discussed in the context of indications of platelet kinetic studies in chronic ITP, before splenectomy is considered.     

Autologous 111 In-labelled platelet sequestration studies in patients with primary immune thrombocytopenia (ITP) prior to splenectomy: a report from the United Kingdom ITP Registry

While splenectomy is an effective therapy for primary immune thrombocytopenia (ITP), possible complications and observed non-complete response (CR) in one-third of patients demonstrate the need for further research into potential pre-surgical predictors of outcomes. Past investigations into platelet sequestration studies, a hypothesized predictive test, have adopted heterogeneous methods and varied widely with regard to power. By studying patients with primary ITP who underwent autologous (111) In-labelled platelet sequestration studies at Barts and The London NHS Trust between 1994 and 2008, we evaluated the effectiveness of sequestration site in predicting short, medium, and long-term CR (platelet count >100 × 10(9) /l) to splenectomy through multivariate (gender, age at splenectomy, and mean platelet lifespan) logistic regression modelling. In total, 256 patients with primary ITP underwent scans; 91 (35·5%) proceeded to splenectomy. Logistic regression revealed significant adjusted odds ratios for CR of 7·47 (95% confidence interval [CI], 1·89-29·43) at 1-3 months post-splenectomy, 4·85 (95% CI, 1·04-22·54) at 6-12 months post-splenectomy, and 5·39 (95% CI, 1·34-21·65) at last follow-up (median: 3·8 years [range: 0·5-13·1 years]) in patients with purely or predominantly splenic versus mixed or hepatic sequestration. These findings demonstrate the utility of autologous (111) In-labelled platelet sequestration studies as an adjunct predictive instrument prior to splenectomy.     

Platelet kinetic studies in patients with idiopathic thrombocytopenic purpura

PURPOSE: To determine the value in diagnosis and treatment of mean platelet life, platelet production, and major sites of platelet destruction in patients with idiopathic thrombocytopenic purpura (ITP). PATIENTS AND METHODS: Sternal or posterior superior iliac spine bone marrow aspiration was performed in 141 patients. Platelet kinetic studies with Indium-111 tropolonate labeled autologous platelets were utilized to determine platelet production. RESULTS: Two subgroups of patients could be defined. The first group (n = 81, 58%) had normal or increased platelet production and increased peripheral platelet destruction. These patients fulfilled the conventional criteria for ITP, including reduced platelet survival time (mean +/- SD, 1.6 +/- 1.4 days). Forty-eight (59%) of these patients had increased splenic sequestration and 30 (88%) of the 34 patients who underwent splenectomy had a complete or partial remission. The second group (n = 60, 42%) had decreased platelet production, with significantly greater platelet survival times (3.6 +/- 2 days, P <0.0001). In this group, the proportion of patients with complete or partial response to splenectomy (62%) was somewhat lower (P = 0.09). These patients mainly had ineffective platelet production in the bone marrow. CONCLUSIONS: Platelet kinetic studies suggest that ITP is a heterogeneous disease that comprises two subgroups. Further studies are needed to validate these findings and to determine their effect on the choice and outcome of therapy.     

The Platelet Destruction Site in Thrombocytopenic Purpuras

The site of sequestration of ⁵¹Cr-labelled platelets has been studied in 465 subjects, of whom 317 suffered from idiopathic thrombocytopenic purpura. The validity of the method was demonstrated in several ways: a given subject usually showed the same site of platelet sequestration when investigated more than once even after a long interval; there were characteristic and very different platelet sequestration curves in the thrombocytopenias due to bone marrow hypoplasia, hypersplenism or ITP; and there was a correlation between the preoperative in vivo results and the radioactivity found in the spleen after splenectomy.
In ITP the destruction of labelled platelets was more often splenic in children and in patients whose thrombocytopenia responded to steroid therapy. There was a perfect correlation between the site of platelet destruction and the platelet rise immediately after splenectomy. There was a good correlation between the site of platelet destruction and the long-term effectiveness of splenectomy.     

The choice of second‐line therapy in steroid‐resistant immune thrombocytopenia: Role of platelet kinetics in a single‐centre long‐term study

Splenectomy is a time‐honoured well established approach for patients with steroid‐resistant immune thrombocytopenia (ITP). However, due to the more recent availability of therapeutic options alternative to splenectomy, such as rituximab and agonists of the thrombopoietin‐receptor, the choice of second‐line therapy is challenging. Platelet kinetics has been widely used to predict response to splenectomy. We describe the outcome of 70 chronic ITP patients who performed a platelet kinetic study after failure of front‐line corticosteroids and subsequently underwent open splenectomy. After a median follow‐up from surgery of 20 years, 62 (88.5%) patients responded to splenectomy and 9 patients (13%) relapsed. Achieving a complete response (CR) significantly predicted a higher probability long‐term stable response. The pattern of platelet sequestration was predominantly splenic in 52 patients (74%), predominantly hepatic in 12 patients (17%), and diffuse in 6 (9%). Patients with nonsplenic (diffuse and hepatic) sequestration showed significantly lower overall responses compared to patients with splenic captation (P = 0.002). A nonsplenic sequestration significantly correlated with lower CR rate and, among CR patients, predicted an increased risk of relapse. Also, the probability of stable responses in nonsplenic uptake patients was substantially lower than in patients with splenic uptake (85% vs. 50%, P = 0.0083). Platelet life span and platelet turnover did not correlate with response and relapse rate. Overall, splenic sequestration was able to predict not only a better quality, but also a higher durability of the responses. However, it should be enphasized that the response rate and duration of response even in patients with nonsplenic uptake were similar or even superior to those reported in patients treated with rituximab as first option. Am. J. Hematol. 89:1047–1050, 2014. © 2014 Wiley Periodicals, Inc.     

Increased number of B-cells in the red pulp of the spleen in ITP

Platelets are targeted by autoantibodies and destroyed in the reticuloendothelial system in the spleen, liver and bone marrow in patients with immune thrombocytopenia (ITP). Other mechanisms such as destruction by cytotoxic T-cells and defective production of platelets in the bone marrow also exist. Splenectomy normalizes the platelet count in 70% of ITP patients, however, precious little is known about the spleen in this disease. Our aim was therefore to investigate the splenic morphology and especially the number and localization of splenic leukocytes in patients with ITP and controls and to evaluate factors predicting outcome of splenectomy. Spleen sections from 29 ITP patients and 11 individuals splenectomized due to trauma were analyzed by immunohistochemistry. All except one of the ITP patients had a normalized platelet count 12 months after splenectomy and the platelet count was inversely correlated with age. ITP patients had an increased number of B-cells in the red pulp. The number of white pulp B-cells and number of T-cells in both compartments was unchanged. In conclusion, B-cells are increased in the red pulp of the spleen and together with cytotoxic T-cells, helper T-cells and macrophages line the sinusoids enabling the immunological attack on platelets in ITP.     

Platelet-associated IgG in immune thrombocytopenic purpura

A method for the measurement of immunoglobulin G associated with gel- filtered platelets is described and finding in 70 control subjects and 37 patients with immune thrombocytopenic purpura (ITP) are reported. Control platelet-associated IgG (PAIgG) levels (nanograms IgG per 10(9) platelets) averaged (+/-SD) 1231+/-424; samples studied after 24 and 48 hr remained within the control range. PAIgG values of 19 adult and 12 childhood patients with chronic ITP averaged 4711+/-3025 and 4923+/- 3955, respectively, and differed significantly from controls (p less than 0.001). There was an inverse correlation between PAIgG values and the chronic ITP patient's platelet count. Six patients with childhood acute ITP had PAIgG levels ranging from 5588 to 56,250 and appeared to represent a different statistical population from those with chronic ITP. In chronic ITP patients responding to splenectomy, there was an immediate normalization of PAIgG levels; however, a certain percentage of patients studied several months after splenectomy evidenced elevated PAIgG levels in association with normal platelet counts. These data showed that the direct measurement of platelet associated antibody is a useful technique in the diagnosis and follow-up of patients with chronic ITP. Preliminary studies in patients with acute ITP have suggested that this method may be useful in differentiating acute and chronic childhood ITP.     

The Sequestration Site of Platelets in Idiopathic Thrombocytopenic Purpura: its Correlation with the Results of Splenectomy

S ummary . The clinical usefulness of external scanning data after infusion of ⁵¹Crlabelled platelets into patients with idiopathic thrombocytopenic purpura (ITP) is a matter of controversy. Observations have been made in 575 patients with ITP. Short-term (6 mth) results of splenectomy were assessed in 206 subjects, and longterm (1-3 yr) in 153. It appears that the site of sequestration is neither a direct function of the severity of the disease nor of the duration of the disease from the clinical onset. Diffuse sequestration, which cannot be taken as an indication for or against splenectomy, is frequently seen in recent and severe cases. Splenic sequestration is more often observed in young patients (72.5% under 30 yr of age) than in older subjects (36% over 30 yr of age).
A good correlation was found between the site of sequestration and the shortand long-term results of splenectomy: success in more than 90% of cases with splenic sequestration but complete failure in 70% with hepatic sequestration. In any patient with ITP splenectomy should be undertaken only after a careful study of the platelet sequestration site.     

Second malignancies in hairy cell leukemia (leukemic reticuloendotheliosis)

Kinetics andw quantification of the sites of destruction of ¹¹¹-Indium-oxine-labeled autologous platelets were investigated in eight patients with idiopathic thrombocytopenic purpura. The mean platelet count was 17 ± 9 × 10⁹/liter; platelets were separated by differential centrifugation and labeled with 5.6 ± 2.5 MBq ¹¹¹In. Whole body and organ ¹¹¹In-platelet distribution was quantitated with a scintillation camera and a computer-assisted imaging system acquisition matrix. Areas of interest were selected with the computer and organ ¹¹¹In-radioactivity expressed as a percentage of whole body activity. Mean platelet survival was 49.5 ± 29.6 hr and the survival curves were exponential. Equilibrium percentage organ ¹¹¹In-radioactivity was (normal values in parentheses): spleen 33.7 ± 8.8(31.1 ± 10.2); liver 16.1 ± 9.5(13.1 ± 1.3); thorax 22.8 ± 3.7(28.2 ± 5.6). Percentage organ ¹¹¹In-activity at the time when labeled platelets had disappeared from the circulation was: spleen 44.5 ± 16.4 (40 ± 16); liver 16.0 ± 11.5 (32.4 ± 7.2); thorax 19.7 ± 6.0 (17.7 ± 10.3). Thorax activity corresponds to bone marrow radioactivity. Three patterns of platelet sequestration were evident. Three patients had mainly splenic sequestration, two mainly hepatic sequestration, and three diffuse reticuloendothelial system sequestration with a major component of platelets destroyed in the bone marrow. Splenectomy was performed in two patients. The pattern of ¹¹¹In-platelet sequestration was not predictive of response of glucocorticoid therapy or indicative of the necessity for splenectomy. Quantitative ¹¹¹In-labeled autologous platelet kinetic studies provide a new tool for the investigation of platelet disorders.     

The scintigraphic index spleen/liver at 30 minutes predicts the success of splenectomy in persistent and chronic primary immune thrombocytopenia

Splenectomy is considered the second-line of treatment in patients with chronic primary immune thrombocytopenia (ITP) in whom glucocorticoids have failed. Some patients do not respond to splenectomy or they have postoperative complications. Based on our previous experience using kinetic and scintigraphic parameters, we did a retrospective study with the aim of comparing all these parameters as a means of predicting the success of splenectomy in persistent and chronic primary ITP. Forty-one consecutive patients with chronic primary ITP refractory to prednisone, who had been splenectomized, were included in the study. The response to splenectomy was assessed by evaluating bleeding and platelet counts before and at different times after surgery. A complete platelet kinetic study was performed before the splenectomy using autologous (111) In-labeled platelets. The scintigraphic parameters measured included different indices between spleen/heart, liver/hearth, and spleen/liver. Thirty-six patients gave a complete response after splenectomy and five patients did not respond. A statistically significant difference between both groups was found with initial platelet recovery and with some scintigraphic indices which also showed a variable prediction value for the success of splenectomy. Among these indices, the spleen/liver at 30 minutes demonstrated a predictive value with a 100% of sensitivity and a 100% of specificity. Conclusion: some platelet kinetic parameters and scintigraphic indices, in particular the spleen/liver at 30 minutes, were useful to predict the outcome of splenectomy in persistent and chronic primary ITP and, therefore, they should be taken into account when deciding whether or not to perform a splenectomy.     

Platelet Survival and Platelet Production in Idiopathic Thrombocytopenic Purpura (ITP)

S ummary . Platelet mean life span (MLS) and platelet production were measured in 3–5 patients with idiopathic thrombocytopenic purpura (ITP) and in 21 healthy subjects.
The mean platelet production in ITP was 2.3 times normal: the highest values were 3–5 times normal. There was a highly significant negative correlation between platelet production and peripheral platelet count. With platelet counts above 50000μl, platelet turnover was within the upper part of the normal range, but with lower platelet counts, turnover progressively increased. It is concluded that the bone marrow in ITP increases platelet production in response to a low platelet count and that this response does not differ from that hitherto known to occur in man and animals rendered thrombocytopenic by thrombopheresis.
The disappearance curve of ⁵¹Cr labelled platelets in ITP consists of two components, a rapid initial one covering the first 15 min after infusion and then a slower one. The pattern was the same whether autologous or homologous platelets were used for labelling. It is suggested that the initial part of the curve does not represent in vivo survival but is due to slight damage to the platelets during the labelling procedure. These slightly damaged cells can resume normal viability when infused into a normal recipient but are rendered less viable when further damaged by platelet antibodies in patients with ITP. This explains the low recovery of infused labelled platelets in ITP recipients, despite the fact that the size of their splenic platelet pool is normal.     

Kinetics and distribution in vivo of 111In-labelled autologous platelets in idiopathic thrombocytopenic purpura

The kinetics of autologous 111In-labelled platelets were studied in 26 patients with ITP. The platelet mean life time (MLT) was considerably shortened, the platelet in vivo recovery slightly lowered and the platelet turnover normal. Comparative studies of the kinetics of simultaneously injected 111In- and 51Cr-labelled platelets in 10 patients showed the MLT and turnover of 51Cr-platelets to be shorter and higher, respectively, than those of 111In-platelets, suggesting that 51Cr-labelling in ITP may underestimate platelet MLT and overestimate platelet turnover. Our results confirm that accelerated platelet destruction is an important pathogenetic factor in ITP, and that the platelet concentration may be influenced by increased splenic platelet pooling and by inability of the bone marrow to respond adequately to the low platelet count. Our scintigraphic studies showed that the spleen played an important role for platelet destruction in most patients, with the liver contributing in some patients.     

Kinetics, in vivo redistribution and sites of sequestration of indium-111-labelled platelets in giant platelet syndromes

Six patients with giant platelet syndrome were examined: four with Bernard-Soulier syndrome (two were asplenic); one with hereditary thrombopathic thrombocytopenia; and one with May-Hegglin anomaly. Autologous platelets were labelled with In-111-oxine and in vivo redistribution and sites of sequestration measured with quantitative imaging. In Bernard-Soulier syndrome platelet survival was normal or moderately shortened; platelet turnover was decreased only in the two patients with thrombocytopenia. In the patients with thrombopathia or May-Hegglin anomaly, platelet survival and turnover was moderately decreased. In those patients with normal-sized spleens, the mean splenic platelet pool consisted of 35.5% of the platelet mass, i.e. normal. The intrasplenic transmit time of the megathrombocytes was prolonged. Splenic blood flow was within normal limits. There was a marked accumulation of platelets in the liver at equilibrium: 15.5-58.8% of whole body radioactivity (normal 9.6 +/- 1.2%). This finding is unexplained. The final sites of sequestration of platelets were mainly in the liver and spleen, similar to that seen in normal subjects. We conclude that there is no inverse relationship between cell size and splenic platelet transit time. Platelet size therefore does not determine the size of the splenic platelet pool. The size of the platelets also does not seem to affect the sites of sequestration at the end of their life span.     

Platelet kinetics with indium-111 platelets: comparison with chromium-51 platelets

The application of 111In-oxine to platelet labeling has contributed to the understanding of platelet kinetics along three lines: 1. It allows the measurement of new parameters of splenic function, such as the intrasplenic platelet transit time, which has shed new light on the physiology of splenic blood cell handling. 2. It facilitates the measurement of platelet life span in conditions, such as ITP, in which 51Cr may undergo undesirable elution from the platelet as a result of platelet-antibody interaction. 3. It allows the determination of the fate of platelets, that is, the site of platelet destruction in conditions in which reduced platelet life span is associated with abnormal platelet consumption, as a result of either premature destruction of "abnormal" platelets by the RE system, or the consumption (or destruction) of normal platelets after their interaction with an abnormal vasculature. Future research using 111In platelets may yield further valuable information on the control as well as the significance of intrasplenic platelet pooling, on the role of platelets in the development of chronic vascular lesions, and on the sites of platelet destruction in ITP. With regard to the latter, methods will have to be developed for harvesting sufficient platelets representative of the total circulating platelet population from severely thrombocytopenic patients for autologous platelet labeling. This would avoid the use of homologous platelets, which is likely to be responsible for some of the contradictory data relating to the use of radiolabeled platelet studies for the prediction of the response of patients with ITP to splenectomy.     

Splenic embolization therapy of idiopathic thrombocytopenic purpura]

21 patients with chronic idiopathic thrombocytopenic purpura (ITP) and 3 patients with Evan's syndrome underwent partial splenic embolization (PSE). 22 patients underwent PSE once, while 2 patients were treated twice, thus a total of 26 procedures were carried out. Follow-up 3 months after embolization was available in all the 24 patients for their response to embolization therapy. 16 patients (67%) achieved complete remission (platelets greater than 100 x 10(9)/L) and 4 (17%) partial remission (platelets greater than 84 x 10(9)/L) after splenic embolization. A total efficacy rate of 83% was observed. This response to embolization after transcatheter vessel occlusion 3 months after is similar to the reported results of splenectomy. Not only may the morbidity and mortality associated with surgical splenectomy be avoided, but also the noninfarcted spleen may continue to provide immunologic functions. The most important experience in this series, however, was the emphasis on partial (60-70%) rather than total splenic arterial embolization. The sequestration site of platelets was associated with the outcome of splenic embolization. More splenic sequestration sites were found in responders, to the therapy.     

The relationship between responsiveness to splenectomy and clinical course after splenectomy in chronic idiopathic thrombocytopenic purpura (ITP)

Fifty-four ITP patients were treated by the protocol proposed by Japanese Idiopathic Disease of Hematopoietic Organ Research Committee. Forty-eight patients were treated with corticosteroid (CS). Twenty-eight patients out of 30 patients who were refractory to CS were splenectomized. To study natural courses of splenectomized patients, 25 patients were splenectomized without elevation of platelet counts at the operation and were followed up their platelet counts and PAIgG for one month without treatment. Clinical courses after splenectomy were classified into four types by the platelet increment followed by splenectomy and the platelet counts at one month after splenectomy; type I (markedly over-shooted platelet peak and normalized platelet counts), type II (moderate platelet peak and 50 approximately 100 x 10(3)/microliters platelets), type III (minimal platelet peak and less than 50 x 10(3)/microliters platelets), and type IV (elevation of platelet counts at day 7 or later of splenectomy and normalized platelet counts). The results of analyses from 25 patients indicated that the numbers of type I, II, III and IV were 10, 5, 6 and 4, respectively. The clinical course of type IV suggests that platelet production may be impaired by anti-platelet antibodies.