EDTA-associated pseudothrombocytopenia: definition and real-world occurrence

Objectives: To better characterize occurrence and extent of anticoagulant-associated pseudothrombocytopenia (PTCP) in the daily routine of a high-throughput clinical laboratory in order to draw conclusions on a more precise definition of this phenomenon. Methods: Concomitant platelet counts in both EDTA and citrate whole blood (WB) performed in our laboratory over a period of four years and 9 months, were analyzed, calculating the correlation, as well as the absolute difference in the results obtained from both materials, cross-referencing these measures with automated flags for platelet aggregates and the results of the visual examination for platelet aggregates of peripheral blood smears. Results: Platelet counts in both materials were strongly correlated (rho=0.86; p<0.0001) but are on average significantly higher in EDTA WB than in citrate WB (median difference: 11 +/- 14.8/nL, p<0.0001). This is in spite of numerous instances of EDTA- associated PTCP recorded in our data, where the opposite is the case. The automated flag for possible platelet aggregates was shown to be very unspecific, while a machine-learning algorithm suggested the difference in platelet counts between EDTA and citrate WB as a predictor of platelet aggregates. Conclusions: EDTA-associated PTCP is a regular occurrence. Differences in platelet counts between EDTA and citrate WB appear to be a far better predictor of PTCP than automated flags. A clear and useful definition of PTCP is still missing, however, and cannot be derived from our data either, indicating the need for further research.