Marked discrepancy of platelet counts between in-hospital and external laboratory testing due to pre-analytical...

Discrepancies in platelet counts between laboratories may lead to diagnostic confusion and unnecessary interventions. We report a case in which platelet counts were consistently normal in an in-house laboratory but repeatedly decreased in external laboratory testing. The patient had no bleeding symptoms, and coagulation findings were normal. Peripheral blood smear examination revealed platelet aggregation in externally processed samples, whereas no aggregation was observed in samples processed immediately in-house. These findings strongly support ethylenediaminetetraacetic acid (EDTA)-dependent pseudothrombocytopenia associated with pre-analytical factors, particularly processing delay. Recognition of this phenomenon is essential to avoid unnecessary investigations and inappropriate management.