Pseudothrombocytopenia masking true thrombocytopenia.

Pseudothrombocytopenia owing to platelet clumping is usually associated with blood specimens anticoagulated with EDTA. It may also be seen if specimens possessing IgM cold agglutinins are processed at room temperature. A patient with a temperature-independent, EDTA-independent agglutinin is reported whose pseudothrombocytopenia was masking true thrombocytopenia. A technique for blood collection when evaluating similar cases is described.