Management of ethylenediaminetetraacetic acid and citrate-dependent pseudothrombocytopenia in the laboratory

This report describes the case of a patient with ethylenediaminetetraacetic acid- (EDTA) and citrate-dependent pseudothrombocytopenia (PTCP). An EDTA tube (BD Vacutainer K2 EDTA; Becton, Dickinson and Company, Franklin Lakes, NJ, USA) platelet count indicated thrombocytopenia (15x109/L and 8x109/L), which was inconsistent with his clinical condition, and prompted further investigation. A repeat sample was drawn into both EDTA tubes and tubes containing 3.2% sodium citrate 9NC coagulation sodium citrate 3.2%, 3.5 mL, Vacuette®, (Greiner Bio-One International GmbH, Kremsmunster, Austria) and immediately measured in the laboratory. The platelet count was 157x109/L and 171x109/L in the EDTA and citrated samples, respectively. Simultaneous peripheral blood smear examinations were performed with capillary, EDTA, and citrated samples. Platelet clumps were observed only in the EDTA sample. The tubes were kept at 25°C and measurements were repeated at 10, 15, 60, 90, and 120 minutes. The platelet counts had decreased by 63% and 76% at the end of 120 minutes in the EDTA and citrated samples, respectively. After 20 minutes at 37°C, the number of platelets had increased by 76% and 87% in the EDTA and citrated samples, respectively. In cases of this kind of a contradiction between laboratory results and clinical status, laboratory specialists should suspect PTCP and be prepared to manage these findings. Close communication between the clinician and the laboratory helps to avoid unnecessary investigation and inappropriate treatment.