Reversible Platelet Aggregation Induced by Low-Temperature Storage in Heparinized Whole Blood Samples

Background/Objectives: Platelet counts can be affected by storage conditions, potentially leading to pseudothrombocytopenia. The present study aimed to investigate temperature-dependent changes in platelet counts and morphology in whole blood samples anticoagulated with heparin or EDTA. We also examined the molecular mechanism of cold-induced aggregation via integrin GPIIb/IIIa-fibrinogen interaction using established bioinformatics technologies (docking simulation). Methods: Peripheral blood was collected from healthy volunteers (n = 6) and treated with either heparin or EDTA. The samples were stored at 4 °C, room temperature, or incubated at 37 °C. Platelet counts were measured using an automated hematology analyzer. The morphology of various blood cells in smears was assessed using the May-Grünwald Giemsa staining method. Docking simulations using an available software (HADDOCK 2.4) were performed to evaluate integrin-fibrinogen binding at different temperatures. Results: In automated blood cell counting, platelet counts in heparinized blood were significantly decreased under low-temperature conditions (4 °C), but this decrease was restored to levels comparable to those at room temperature upon warming to 37 °C (p < 0.05). No significant changes were observed in EDTA-treated samples. Microscopical findings showed platelet aggregation only in heparinized samples at 4 °C, with normal morphology restored upon warming (37 °C). Docking simulations estimated stronger integrin GPIIb/IIIa-fibrinogen binding at 4 °C than at 37 °C (p = 0.0286), suggesting temperature-dependent enhancement of molecular interactions. Conclusions: These findings indicate that heparin can induce reversible platelet aggregation at low temperatures in whole blood samples, leading to pseudothrombocytopenia. This phenomenon may be mediated by increased integrin GPIIb/IIIa-fibrinogen binding.