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Thrombopoietin (TPO) is the major regulator of megakaryopoiesis. Measurement of serum TPO levels may help distinguish between various causes of thrombocytopenia and predict treatment response to TPO receptor agonists. Serum TPO levels from 118 healthy volunteers and 88 patients with abnormal platelet counts were measured using a quantitative ELISA assay. The mean (range) TPO level in healthy volunteers was 39 (7-99) pg/mL. TPO values were correlated with the patient's diagnosis, platelet count, and response to TPO receptor agonists. 88 patients with history of consumptive thrombocytopenia (39) or hypoproliferative thrombocytopenia (49) were analyzed. Median (interquartile range) TPO level for consumptive thrombocytopenia patients was 63 (48-98) pg/mL with a corresponding median (interquartile range) platelet count of 73 (28-146) 3 10 9 /L. In contrast, hypoproliferative thrombocytopenia patients had platelet counts [59 (30-117) 3 10 9 /L] comparable with consumptive thrombocytopenia patients, but significantly higher serum TPO levels [706 (358-1546) pg/mL, P < 0.0001]. Analysis of 21 ITP patients treated with TPO receptor agonists demonstrated that a TPO level >95 pg/mL was associated with lack of clinical response (P < 0.002). TPO levels may have diagnostic utility in discriminating between patients with hypoproliferative and consumptive thrombocytopenia. Elevated TPO levels in ITP patients may predict a poor clinical response to treatment with TPO receptor agonists. Am. J. Heamtol. 88:1041Heamtol. 88: -1044Heamtol. 88: , 2013. V C 2013 Wiley Periodicals, Inc. IntroductionThrombopoietin (TPO) is the major regulator of platelet production. Prior studies in animal models [1-3] and humans [4] have demonstrated that TPO levels vary inversely with circulating platelet mass. Additional clinical studies have suggested that TPO levels also vary inversely with the rate of megakaryopoiesis [5][6][7][8][9][10]. Thus, TPO levels may help distinguish between the various disorders of thrombocytopenia, with elevated TPO levels associated with hypoproliferative thrombocytopenia (e.g., aplastic anemia) but normal TPO levels associated with consumptive thrombocytopenia (e.g., immune thrombocytopenia) [5][6][7][8]10]. In addition, the introduction of TPO receptor agonists for the treatment of thrombocytopenia has created an interest in predicting the response of patients to these agents [11]; TPO levels may help predict treatment responses.To assess the performance characteristics of a TPO assay in a clinical setting, we measured the serum TPO concentration in a panel of healthy humans as well as patients with diverse hematologic diseases. We then correlated the TPO level with platelet count, diagnosis, and treatment response. Our goals were (1) to determine the normal range of TPO levels, (2) to determine whether TPO levels could help discriminate between different disorders of platelet production, and (3) determine whether TPO levels might help predict the platelet response in those patients treated with a TPO receptor agonist ...

Inhibitors of FVIII are usually IgG polyclonal antibodies that develop as alloimmune responses in patients with congenital haemophilia A or as autoimmune responses resulting in acquired haemophilia. Their recognition can be difficult, especially when the titre is low. Furthermore, results from a Bethesda assay often require several days as samples are referred to a specialty laboratory. The aim of this study is to assess the utility of an ELISA system for detecting immune responses to FVIII. A total of 246 plasma samples submitted from 176 individuals with immune responses to FVIII, as verified with the Bethesda assay, and samples from 50 control subjects were tested for the presence of FVIII-specific IgG using an ELISA-based assay. Paired sera from 18 of the patients were also tested by the ELISA. Of the 246 samples that were positive for a FVIII inhibitor by the Bethesda assay, 235 (95.5%) were also positive by ELISA. The regression coefficient, using Log BU was r = 0.82. The correlation data were strengthened when 27 inhibitor samples were diluted further. There was a strong correlation between ELISA results for the 18-paired serum and plasma samples (r = 0.99). There is a strong correlation between the ELISA and Bethesda methods in detecting immune responses to FVIII. The ELISA provides rapid screening that could be available well in advance of confirmation by the Bethesda assay.

A 30-year-old female with severe factor XI deficiency of 0-2% acquired factor XI inhibitor following many infusions for fresh frozen plasma (FFP) for surgical procedures starting at 4 years of age. Seven months before this inhibitor was diagnosed, surgery was complicated by prolonged bleeding resistant to FFP, requiring epsilon aminocaproic acid (EACA) and surgical packing. The inhibitor was measured at 2.2 Bethesda units, 7 months since the last FFP. The inhibitor was confirmed as specific anti-XI and anti-XIa binding by patient's IgG to immobilized factor XI and factor XIa from whole plasma and purified IgG. For repair of a painful anterior cruciate ligament (ACL) defect she was given recombinant factor VIIa (rVIIa) at 90 mug kg(-1), starting one-half hour preoperatively and continued every 2 h for 8 h when haemostasis was complete. Thereafter the rVIIa was given every 3 h for two doses, and then every 4 h for four doses at which time she was discharged on EACA which was continued for 6 days. There was excellent haemostasis during and following the surgery. There was no evidence of consumptive coagulopathy, with no change in the fibrinogen, platelet count, or D-D dimer; and no increase of platelet factor 4, beta-thromboglobulin, or prothrombin fragment F 1.2. The thrombin-antithrombin complex increased over baseline after 24 h. There was no postoperative deep vein thrombosis or pulmonary embolus. In this patient with a factor XI inhibitor, the recombinant factor VIIa was effective and safe, ensuring adequate haemostasis with no thrombotic complications. This product which was designed for patients with inhibitors to factor VIII or factor IX, and factor VII deficiency, has now been given successfully to four patients with factor XI inhibitors.

The objective of this study was to assess the effect of protein A immunoabsorption in terms of response rate and toxicities in patients with classical thrombotic thrombocyto-penic purpura (TTP) refractory to therapeutic plasma exchange. The study included nine females and one male with a diagnosis of classical TTP treated at multiple university hospital centers with protein A immunoabsorption (PAI) after having failed plasma exchange. The 10 patients had an age range 17-62 years. Prior to PAI, the patients had failed to respond to a mean of 15 (range 6-39) therapeutic plasma exchanges. Three patients had previous episodes of TTP. Evaluation for response to PAI included serial measurements of serum creatinine, lactate dehydrogenase (LDH), hemoglobin, hematocrit, and platelet count before, during, and up to 18 months post-PAI treatment. Seven of 10 study patients had resolution of their TTP. Six of the patients required six or fewer therapeutic PAIs and one required 12 treatments. All responding patients had evidence of improvement by the third PAI treatment. Three patients demonstrated no response to PAI, with two patients expiring from complications of TTP and one patient demonstrating a complete response to a subsequent therapy. No significant toxicity was noted with the use of PAI in this setting. Protein A immunoabsorption in patients with classical TTP refractory to plasma exchange can produce durable complete remissions and warrants comparative studies.