Initial Laboratory Findings Useful for Predicting the Diagnosis of Chronic ITP: Results of a Multicenter Prospective Study.

Abstract

Idiopathic thrombocytopenic purpura (ITP) is one of the major causes of thrombocytopenia. Currently, the diagnosis of ITP is principally based on the exclusion of other possible concurrent causes of thrombocytopenia. In the guidelines proposed by the American Society of Hematology, the panel recommended that no specific laboratory tests are considered necessary for the diagnosis. However, availability of reliable laboratory assays should be helpful in supporting the diagnosis of ITP. Recently, 2 of us (MK and YI) reported that erythrocyte count, leukocyte count, anti-GPIIb/IIIa antibody-producing B cells, platelet-associated anti-GPIIb/IIIa antibodies, reticulated platelets and thrombopoietin measured at first visit were useful to predict a future diagnosis of chronic ITP (manuscript submitted). To confirm this, we conducted a multicenter prospective study involving 113 patients with thrombocytopenia and a normal peripheral blood film at first visit. Patients with clinically apparent associated conditions that can cause thrombocytopenia were excluded. Each patient underwent physical examination and routine laboratory tests, and was prospectively followed for >6 months. Anti-GPIIb/IIIa antibody-producing B cells, platelet-associated anti-GPIIb/IIIa antibodies, reticulated platelets and plasma thrombopoietin were also examined at first visit. Clinical diagnosis was made in a blinded fashion based on bone marrow findings and the clinical course. Eighty-nine patients were diagnosed as having chronic ITP, and 24 had a non-ITP disorder, including 11 with aplastic anemia (AA), 10 with myelodysplastic syndrome (MDS), and one each with Fanconi anemia, May-Hegglin anomaly and myelofibrosis. Six laboratory findings were identified as initial parameters that discriminated future diagnosis of chronic ITP from non-ITP. These included the absence of anemia, absence of leukopenia, increased anti-GPIIb/IIIa antibody-producing B cell frequency, increased platelet-associated anti-GPIIb/IIIa antibodies, elevated reticulated platelet percentage and normal or slight increase of thrombopoietin (all for P < 0.001). Stepwise multiple regression analysis revealed that anemia, anti-GPIIb/IIIa antibody-producing B cell frequency, reticulated platelet percentage and thrombopoietin were factors that independently contributed to the later diagnosis of chronic ITP. Three or more of 6 ITP-associated laboratory findings were present at presentation in 78 (93%) patients later diagnosed as chronic ITP, compared with 6 (25%) patients whose disorder was non-ITP (P < 10−5). All 6 “false-positive” patients were diagnosed as AA or MDS, but 4 of them probably had overlapping immune thrombocytopenia. In summary, this multicenter prospective study confirms usefulness of 6 laboratory tests for the diagnosis of chronic ITP. The identification of ITP-associated laboratory findings encourages the future development of reliable diagnostic criteria for chronic ITP.