Electron microscopy examination of platelet whole mount preparations to quantitate platelet dense granule numbers: Implications for diagnosing suspected platelet function disorders due to dense granule deficiency.

INTRODUCTION Dense granule (DG) deficiency (DGD) is a feature of some platelet function disorders (PFD) with a prevalence similar to von Willebrand disease. Most laboratories assess for DGD using whole mount platelet preparations and electron microscopy (EM). We evaluated our experiences with this test and associations between DGD and bleeding. METHODS Dense granule EM records for 2006-2017 were examined for patients and simultaneously tested controls, and for an overlapping PFD study cohort to evaluate findings and their relationship to bleeding. RESULTS More patient than control samples had reduced DG counts (6.5% vs 0.3%, P < .01). DG counts showed no relationship to age or mean platelet volume and had acceptable within-subject variability that was higher for DGD than control participants (28% vs 12%). Repeat tests confirmed DGD in all persons with initial DG counts <4.0/platelet, but not in those with less severe reductions (4.0-4.8 DG/platelet) or normal DG counts (≥4.9 DG/platelet). Aggregometry and adenosine triphosphate release tests, respectively, had only ~52% and 70% sensitivity for DGD. Confirmed DGD by EM was associated with higher bleeding scores and a bleeding disorder. CONCLUSION Whole mount EM is useful for the evaluation of suspected PFD due to DGD and detects abnormalities associated with bleeding.