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Acquired disorders of platelet function are an underdiagnosed cause of bleeding tendency. A 14-year-old girl developed moderate mucocutaneous bleeding two weeks after a Mycoplasma pneumoniae infection successfully treated with clarithromycin. The patient was referred to us 7 months later for laboratory investigation of the persisting bleeding diathesis. The patient's personal and family histories were negative for bleeding disorders. Complete blood count, von Willebrand Factor levels and coagulation tests were normal; platelet aggregation, ATP secretion, δ-granules content and serum thromboxane B2 levels were defective. At follow-up visits, laboratory parameters and the bleeding diathesis progressively normalized within 2 years. The patient's condition is compatible with a diagnosis of acquired Storage Pool Deficiency (SPD), associated with defective thromboxane A2 production. To our knowledge, this is the first case of acquired, transient SPD with spontaneous remission. The pathogenic role of Mycoplasma pneumoniae infection or clarithromycin is possible, albeit uncertain.

A variety of laboratory tests have been developed, which can diagnose a number of both congenital and acquired disorders of platelet function. Many tests of platelet function measure the ability of platelets to adhere to each other, forming platelet aggregates, which represent the major constituents of hemostatic plugs and of arterial thrombi. Light transmission aggregometry (LTA) is still considered the gold standard of platelet aggregation tests, but other platelet aggregation-based tests are also available. Among them, the flow cytometry-based methods may be more convenient than LTA for the study of patients with very low or very high platelet counts. The use of platelet aggregation tests has also been advocated to monitor the treatment with antiplatelet agents (mostly the P2Y 12 antagonist clopidogrel) of patients with thrombotic arterial occlusions, with the aim of improving their efficacy and safety. However, randomized clinical trials failed to show any advantage of this strategy; as a consequence, international guidelines now recommend against laboratory monitoring of antiplatelet therapy.