The patient's blood should be redrawn using a citrated tube. She has pseudothrombocytopenia as shown on the peripheral blood smear, a condition that leads to the formation of platelet clumps in vitro. This in vitro occurrence is caused by the presence of ethylenediaminetetra-acetic acid (EDTA) agglutinins, which naturally occur in approximately 0.1% of the population and lead to platelet clumping. The automated platelet counter does not recognize the clumps as masses of platelets, and the platelet count is, therefore, spuriously low. Drawing a complete blood sample into a citrate- or heparin-anticoagulated tube may resolve the clumping.
Prednisone and methylprednisolone are first-line agents for treating adults with immune (or idiopathic) thrombocytopenic purpura (ITP) who require therapy. ITP is an acquired autoimmune condition in which autoantibodies are directed against platelet surface proteins, leading to platelet destruction that may be only partially counteracted by increased bone marrow platelet production. Variants of ITP may be drug induced or part of a broader illness of abnormal immune regulation, as with systemic lupus erythematosus, HIV infection, or lymphoproliferative malignancies. Therapy may be required for patients with platelet counts lower than 30,000 to 40,000/µL (30-40 × 109/L) or with bleeding. Because this patient most likely does not have ITP, diagnostic testing for systemic lupus erythematosus with antinuclear antibody or HIV testing is not indicated.
Plasma exchange would not benefit this patient. Thrombotic thrombocytopenic purpura (TTP) is a process characterized by abnormal activation of platelets and endothelial cells, deposition of fibrin in the microvasculature, and peripheral destruction of erythrocytes and platelets. Most patients with the typical sporadic form of TTP have developed autoantibodies directed against the protease that cleaves the high-molecular-weight multimers of von Willebrand factor. Initial treatment consists of plasma exchange. Because this patient has platelet clumping on the peripheral blood smear and no evidence of schistocytes characteristic of TTP-associated microangiopathic hemolysis, the diagnosis of TTP is unlikely and plasma exchange is unnecessary.
