Association of pseudothrombocytopenia and pseudoleukopenia: evidence for different pathogenic mechanisms.

A case of spurious automated leukocyte and platelet counts due to EDTA-dependent platelet-neutrophil agglutination is described. Whole blood anticoagulated with K3EDTA, sodium citrate and lithium heparin was analysed at short time intervals up to 6 h from sampling at 37 degrees C and at room temperature (RT = 27 degrees C). A phenomenon of platelet clumping occurred at both temperatures with all the anticoagulants (pseudothrombocytopenia), while platelet-granulocyte agglutination was present only with EDTA at RT. Aggregates consisting of up to 80 neutrophils were seen on the blood smear. The contemporary presence of platelet clumping caused a reduction of WBC count of only 25% the initial, while leukocyte differential was markedly altered (pseudolymphocytosis). Further experiments were performed mixing plasma and serum of the patient with packed cells (PC) from a normal donor in the presence of different anticoagulants and at various dilutions and temperatures. Platelet-neutrophil agglutination occurred only in the presence of EDTA at temperatures lower than 37 degrees C, and was abolished by plasma dilutions from 1:8 onwards. Similarly, it was inhibited by incubation with dithiothreitol (DTT), in contrast with platelet clumping. The latter phenomenon was triggered by an EDTA concentration lower than that necessary to cause platelet-neutrophil agglutination (0.5 mg ml-1 vs. 0.77 mg ml-1). Obtained results suggest the causal association of 2 different phenomena, both transferable to normal cells by means of patient plasma and serum. In the article the pathogenetic implications of the case are discussed.