Association of pseudothrombocytopenia and pseudoleukopenia: Evidence for different pathogenic mechanisms

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Abstract
Moraglio D, Banfi G, Arnelli A. Association of pseudothrombocytopenia and pseudoleukopenia: evidence for different pathogenic mechanisms. Scand J Clin Lab Invest 1994; 54: 257-65 A case of spurious automated leukocyte and platelet counts due to EDTA-dependent platelet-neutrophil agglutination is described. Whole blood anticoa-gulated with K3EDTA, sodium citrate and lithium heparin was analysed at short time intervals up to 6 h from sampling at 37 °C and at room temperature (RT = 27 °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 (pseudolym-phocytosis). 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 °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 (0.5mg ml−1 vs. 0.77mg 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.