Some individuals show thrombocytopenia on the hematology CBC autoanalyzers, but a manual examination reveals normal counts. This is pseudothrombocytopenia, and most pathology textbooks explain the causes of the low counts reported by the autoanalyzers.
One of the important causes is EDTA-induced platelet aggregation. Some individuals have IgG autoantibodies against a cryptic platelet antigen, likely to be a glycoprotein IIB/IIIA complex [Ali and Auerbach, 2017; Bobba and Doll, 2012]. It has a reported incidence of 0.09-0.21% [Yoneyama and Nakahara, 2003], but may be higher in some places. In susceptible persons, EDTA exposes the cryptic antigen to the antibodies, resulting in platelet aggregation. The autoanalyzer is unable to count the aggregated platelets correctly, and falsely reports thrombocytopenia.
This pseudothrombocytopenia is an in vitro phenomenon. Unfortunately, the low counts recur if the test is repeated.
Modern autoanalyzers can flag samples with platelet clumping. The pathologist must make a slide and manually examine it before releasing the report. Some accreditation bodies insist that manual examination of slides should be carried out in all cases of thrombocytopenia reported by the autoanalyzer.
Although not all accreditation bodies insist on manual confirmation of thrombocytopenia, I feel that accreditation bodies should demand this procedure. Patients have been known to undergo platelet transfusions, and even splenectomy to treat the low platelet counts: needless and potentially harmful interventions that can be avoided by a look at a slide.
References
Ali N, Auerbach HE. New-onset acute thrombocytopenia in hospitalized patients: pathophysiology and diagnostic approach. J Community Hospital Internal Medicine Perspectives, 2017;7(3):157-67.
Bobba RK, Doll DC. Platelet satellitism as a cause of spurious thrombocytopenia. Blood 2012;119:4100.
Yoneyama A, Nakahara K. EDTA-dependent pseudothrombocytopenia–differentiation from true thrombocytopenia. Nihon Rinsho. 2003 Apr;61(4):569-74 (Abstract).
SK Sood
December 2017
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I’ve seen many and agree a manual slide review is required. That is post a redraw as I have seen many altered counts by the simple use of a wooden stick.
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