Spurious leukocytosis and thrombocytopenia. A dual phenomenon caused by clumping of platelets in vitro.

Three patients with spurious thrombocytopenia caused by in vitro clumping of platelets also had leukocytosis that was inappropriate for their clinical state and could not be verified on examination of a blood smear. Serial blood counts and analysis of the platelet and WBC histograms proved the "leukocytosis" to be spurious and caused by platelet clumps erroneously "recognized" by the counter as white blood cells. In three additional patients, the WBC counts increased concomitantly with a decrease in their platelet counts but remained within the normal range. Abnormal platelet and WBC counts generated by automated cell counters must be verified by examination of a blood smear before patients are subjected to unwarranted investigations and therapy.