Which of the following can cause a falsely decreased platelet count?

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Platelet clumps lead to a falsely decreased automated platelet count because the analyzer counts discrete particles, and clumped platelets are usually counted as fewer events (or as one) than many individual platelets, so the reported count drops even though the circulating platelets are adequate. This is a classic EDTA-related pseudothrombocytopenia phenomenon—the smear may show platelet aggregates while the patient’s true platelet number is normal. To address this, redraw in a different anticoagulant (like citrate) or verify with a manual smear examination to confirm actual platelet number. The other options don’t typically cause a spuriously low count: schistocytes reflect red cell fragmentation, normal platelet morphology wouldn’t reduce the count, and giant platelets can sometimes affect counts depending on the analyzer but aren’t the common source of a false decrease like clumping is.