Background: Pseudothrombocytopenia is a spurious thrombocytopenia caused mostly by ethylenediaminetetraacetic acid (EDTA) use, and if detected early, unnecessary testing and treatment can be avoided. We present pseudothrombocytopenia caused by EDTA and citrate in an asymptomatic healthy child, as well as the value of using peripheral blood smear, platelet histogram, and flag data.
Case: A previously healthy 13-year-old girl with thrombocytopenia who developed tonsillitis 12 days previously was referred to our hematology department. Laboratory tests revealed severe thrombocytopenia (17x103/µL) in EDTA samples. A peripheral blood smear revealed numerous platelet clumping. We hypothesized EDTA-dependent pseudothrombocytopenia and ordered a platelet count by citrate tube. A citrate tube revealed thrombocytopenia with a platelet count of 55x103/µL. The platelet count (175x103/µL) returned to normal with heparin tubing. All blood samples had a similar platelet histogram and flags in the autoanalyzer. The platelet histogram indicated a serrated/sawtooth curve containing the largest platelet aggregates. Platelet flags alert messages about platelet clumping.
Conclusions: Peripheral blood smear is the most reliable test for pseudothrombocytopenia. If the physician has no experience with smear examination, both laboratory technician and physician should be aware of abnormal platelet histograms and platelet clumping messages in platelet flags, which indicate pseudothrombocytopenia.
Keywords: child; platelet flags; platelet histogram; pseudothrombocytopenia.