American Board of Internal Medicine (ABIM) Certification Practice Exam

What condition can platelet clumping indicate when assessing a blood sample?

1. True thrombocytopenia

2. Myeloproliferative disorders

3. Pseudothrombocytopenia

4. Immune thrombocytopenia

The correct answer is: Pseudothrombocytopenia

Platelet clumping is primarily associated with pseudothrombocytopenia, which occurs when platelets aggregate in vitro, leading to a falsely low platelet count in automated blood cell counters. This phenomenon often arises due to the presence of specific antibodies that can cause platelets to clump together during the blood sample processing, particularly in EDTA (ethylenediaminetetraacetic acid) anticoagulated specimens. In the case of a blood test revealing low platelet counts, careful examination of the blood smear is crucial. If clumping is observed in the smear, it suggests that the low platelet count does not represent true thrombocytopenia (an actual decrease in the number of platelets) but rather the result of this in vitro effect. Therefore, identifying clumping can prevent unnecessary interventions for presumed thrombocytopenia. Myeloproliferative disorders and immune thrombocytopenia, while they can also affect platelet counts, typically do not lead to the artifact known as pseudothrombocytopenia. True thrombocytopenia represents a genuine reduction in platelet numbers without the influence of clumping due to in vitro effects. Understanding the context and mechanics of how platelets behave in various environments is essential for accurate diagnosis and treatment decisions