Background Thrombocytopenia is a major haematologic complication in patients with systemic lupus erythematosus (SLE). The mechanisms underlying thrombocytopenia observed in SLE is heterogeneous, but immune thrombocytopenic purpura (ITP) is the most common. Other potential mechanisms include thrombotic microangiopathy (TMA), consumption coagulopathy, hemophagocytic syndrome, and impaired thrombopoiesis. In clinical setting, it is imperative to make prompt differential diagnosis of thrombocytopenia to provide adequate treatment. We have previously reported that detection of anti-GPIIb/IIIa antibody-producing cells, reticulated platelets, and thrombopoietin (TPO) in circulation is useful for discriminating ITP from other causes. This enables us to develop an algorithm for differential diagnosis of thrombocytopenia based on comprehensive laboratory tests using peripheral blood (Figure 1).
Objectives To validate our preliminary algorithm using a prospective cohort of consecutive SLE patients with thrombocytopenia.
Methods We conducted a prospective study involving 41 consecutive SLE patients who visited our hospital because of thrombocytopenia (<100x109/L) between 2008 and 2011. At presentation, peripheral blood samples were sent to our laboratory to evaluate a series of blood smear, coagulation, and immunologic tests. Final diagnosis of thrombocytopenia was made later by experienced rheumatologists who were blinded to assay results, taking account of clinical course over at least 6 months, including bone marrow examination and therapeutic responses.
Results The number of patients who were categorized into individual diagnoses based on the algorithm is shown in Figure 1. Clinical diagnoses included ITP in 24, drug-induced thrombocytopenia in 5, consumption coagulopathy in 3, TMA in 2, amegakaryocytic thrombocytopenia in 2, hemophagocytic syndrome in 2, pseudothrombocytopenia in 2, and myelodysplastic syndrome in one. A concordance rate of algorithm-based and clinical diagnosis was 89% (32/36) when 5 patients with drug-induced thrombocytopenia were excluded. All 4 patients with the discordant diagnosis were clinically diagnosed as having ITP, but were unclassified by the algorithm. Five patients with drug-induced thrombocytopenia were classified as having impaired thrombopoiesis (n=3), unclassified (n=1), or ITP (n=1) according to the algorithm.
Conclusions Our clinically relevant algorithm is useful for differential diagnosis of thrombocytopenia in SLE patients. These results warrant further studies on a larger number of patients.
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Disclosure of Interest None declared