Evaluating Vortexing Times to Disaggregate Platelet Clumps in EDTA Specimens

ABSTRACT EDTA-dependent pseudothrombocytopenia (PTCP) causes spurious low platelet counts, necessitating costly repeat testing and patient recollections. This study evaluated the efficacy of varying vortexing durations to mechanically disaggregate platelet clumps and restore accurate counts. A total of 120 adult EDTA-anticoagulated specimens flagged for platelet clumps by a Beckman Coulter DxH 900 were included. Samples were assigned to 1-, 2-, or 3-minute vortexing groups. Peripheral blood smears were reviewed pre- and postvortex to confirm the presence of clumps and assess disaggregation. The analyzer’s platelet clump flag demonstrated a low positive predictive value (34.2%), with only 41 samples containing true clumps. Among these true-positive samples, successful disaggregation occurred in 29% of samples in both the 1-minute and 3-minute groups, with no statistically significant difference in efficacy across durations (P = .09). All other complete blood cell count parameters remained stable postvortexing (Pearson r > 0.99). However, vigorous agitation induced new platelet clumps in 29% of samples that were initially clump negative. These findings suggest that although vortexing is a viable noninvasive corrective action that can resolve true PTCP cases, it is not without risk. Therefore, a “smear-first” protocol is recommended, in which microscopic confirmation of clumps precedes mechanical disaggregation to avoid inducing artifacts in false-positive specimens.