A 39-year-old woman with type 2B von Willebrand disease (VWD) (baseline platelet count, ∼100 × 10⁹/L) admitted for gastrointestinal bleeding is found to have a platelet count of 14 × 10⁹/L. Repeat platelet count performed on citrated and heparin tubes was <10 × 10⁹/L, prompting platelet transfusion. The hematology fellow was called, and the peripheral blood film was reviewed with electronic software (CellaVision DI-60), finding no platelets. After 3 platelet transfusions failed to raise the platelet count, the hematology attending was notified. The attending examined a physical peripheral blood film, finding a single massive platelet clump (panels A-C; Wright-Giemsa stain, original magnification: ×10 [A], ×50 [B], ×100 [C]) visible to the naked eye (panel D, arrow) accounting for >95% of the platelets present on the slide.

Patients with type 2B VWD can have circulating platelet agglutinates in vivo as well as spontaneous in vitro platelet clumping pathophysiologically distinct from typical EDTA-dependent pseudothrombocytopenia. Clumping may occur irrespective of the anticoagulant present in the tube. Given the COVID-19 pandemic-induced shift toward electronic slide review software, this case also illustrates the importance of reviewing the physical peripheral blood film with a microscope when looking for platelet clumps, given that electronic software may only allow review of a small section of the slide, and therefore, large clumps can be missed.