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However, PS and platelet clumps were significantly decreased, even though a few attached platelets to neutrophil membrane and small portions of platelet clumps were still observed (Figure 2A). These platelet aggregates may detach from the neutrophil membrane and form free platelet clumps, which explains the co-existence of both PS and platelet clumps in the blood smear. [Extracted from the article]

Ethylenediaminetetra-acetic acid (EDTA) is widely used as anticoagulant in laboratory medicine. EDTA-dependent pseudothrombocytopenia is a rare phenomenon (i.e., around 0.1% in the general population), which is mostly due to the presence of EDTA-dependent antiplatelet antibodies that react optimally between 0°C and 4°C, recognize the cytoadhesive receptors gpIIb-IIIa, stimulate the expression of activation antigens, trigger activation of tyrosine kinase, platelet agglutination and clumping in vitro, which finally lead to a spuriously decreased platelet count. The reliable and timely identification of this artifact is essential, since there a high chance that it may be confused with other life-threatening platelet disorders, or otherwise lead to inappropriate clinical and therapeutic decision-making. Five basic criteria should be fulfilled to raise the clinical suspicion of EDTA-dependent pseudothrombocytopenia, i.e., (i) abnormal platelet count, typically <100×109/L; (ii) occurrence of thrombocytopenia in EDTA-anticoagulated samples at room temperature, but to a much lesser extent in samples collected with other anticoagulants and/or kept warmed at ∼37°C; (iii) time-dependent fall of platelet count in the EDTA specimen; (iv) evidence of platelet aggregates and clumps in EDTA-anticoagulated samples with either automated cell counting or microscopic analysis; (v) lack of signs or symptoms of platelet disorders. Several remedies have been proposed, such as warming the sample to 37°C or using additives or specific formulations of anticoagulants including buffered sodium citrate, heparin, ammonium oxalate, β-hydroxyethyltheophylline, sodium fluoride, CPT (trisodium citrate, pyridoxal 5′-phosphate and Tris), antiplatelet agents, potassium azide, amikacin, kanamycin or other aminoglycosides, and calcium replacement with the simultaneous addition of calcium chloride/heparin. According to available evidences, the most suitable and practical approach so far for most clinical laboratories seems, however, the recollection of blood samples using sodium citrate, CPT or calcium chloride/heparin as additives, maintaining the specimen at 37°C until the platelet count has been completed. [ABSTRACT FROM AUTHOR]

Background: The prevalence and course of pseudothrombocytopenia in outpatients is uncertain. Methods: In a cohort study of 687,955 members of a health maintenance organization, we extracted 36,780 consecutive automated complete blood count test results and determined the point prevalence of pseudothrombocytopenia during a one-month period. We also calculated a retrospective cumulative prevalence over the past 5 years. Results: There were 1105 (2.7%) patients with platelet counts of 100-149×109/L and 304 (0.8%) with counts <100×109/L, of whom 12.8% (n=39) had pseudothrombocytopenia newly discovered or in the past. There were 40 additional patients with a history of pseudothrombocytopenia, but now showing platelet counts of 150×109/L or more, and another 21 with platelet counts of 100-149×109/L. The total cumulative prevalence of pseudothrombocytopenia was 0.27% (100/36,780), 2.5-fold higher than the point prevalence of 0.11% (39/36,780). Platelet counts were extremely variable in these patients during the 5-year follow-up period. Conclusions: Physicians should be aware of the variability of platelet counts in patients with pseudothrombocytopenia in order to reduce unnecessary retesting. Since pseudothrombocytopenia can result in platelet counts between 100 and 149×109/L, peripheral smears should be done in all patients with such values, or the reference limit value should be lowered to 100×109/L. [ABSTRACT FROM AUTHOR]

This article reports on a study which evaluated ready-to-use tubes containing sulfate magnesium, called Thromboexact, with a flag suggesting a possible ethylene diamine tetracetic acid (EDTA)-dependent pseudothrombocytopenia (PTCP). It is noted that PTCP is an in vitro phenomenon of platelet clumping that leads to low platelet counts by hematology analyzers. The study concluded that the use of Thromboexact must be considered in the case of an in vitro massive platelet aggregation due to EDTA.

A letter to the editor is presented which discusses the case of a 34-year-old patient with suspected heparin-induced thrombocytopenia who developed thrombocytopenia after heparin administration.