pseudothrombocytopenia

Pseudothrombocytopenia is a laboratory artifact in which automated platelet counters report a low platelet count due to in vitro platelet clumping, most commonly in blood collected in ethylenediaminetetraacetic acid (EDTA) anticoagulated tubes. It is not a true thrombocytopenia; the patient’s platelets are usually adequate and hemostasis is typically normal.

Mechanism and features: In the presence of EDTA, some individuals have autoantibodies against platelet glycoproteins (such as GPIIb/IIIa or GPIb/IX) that cause platelets to aggregate. When a blood sample with EDTA is analyzed, clumped platelets are often counted as fewer platelets or as larger particles, producing a spuriously low platelet count. The phenomenon is most frequently EDTA-dependent but can be seen with other anticoagulants in rare cases. A peripheral smear may reveal platelet aggregates.

Diagnosis: Diagnosis is suggested by a discordance between a low automated platelet count and a normal reading on smear examination, which shows platelet clumps rather than true megakaryocytic failure. Confirmation is achieved by repeating the platelet count using an alternative anticoagulant (such as citrate or heparin) or by manual counting; normal platelet numbers on the repeat test support pseudothrombocytopenia. Flow cytometry or platelet function tests are not routinely required.

Management and implications: Pseudothrombocytopenia does not require treatment and carries no increased bleeding risk. Clinicians should avoid relying on EDTA-containing samples when discordant results are found, and use alternative anticoagulants for confirmation or document the artifact in the medical record. If true thrombocytopenia is suspected due to clinical signs or additional testing, standard evaluation for other causes should proceed.