A case of EDTA-dependent pseudothrombocytopenia: simple recognition of an underdiagnosed and misleading phenomenon
© Nagler et al.; licensee BioMed Central Ltd. 2014
Received: 25 October 2013
Accepted: 17 April 2014
Published: 1 May 2014
EDTA-dependent pseudothrombocytopenia (EDTA-PTCP) is a common laboratory phenomenon with a prevalence ranging from 0.1-2% in hospitalized patients to 15-17% in outpatients evaluated for isolated thrombocytopenia. Despite its harmlessness, EDTA-PTCP frequently leads to time-consuming, costly and even invasive diagnostic investigations. EDTA-PTCP is often overlooked because blood smears are not evaluated visually in routine practice and histograms as well as warning flags of hematology analyzers are not interpreted correctly. Nonetheless, EDTA-PTCP may be diagnosed easily even by general practitioners without any experiences in blood film examinations. This is the first report illustrating the typical patterns of a platelet (PLT) and white blood cell (WBC) histograms of hematology analyzers.
A 37-year-old female patient of Caucasian origin was referred with suspected acute leukemia and the crew of the emergency unit arranged extensive investigations for work-up. However, examination of EDTA blood sample revealed atypical lymphocytes and an isolated thrombocytopenia together with typical patterns of WBC and PLT histograms: a serrated curve of the platelet histogram and a peculiar peak on the left side of the WBC histogram. EDTA-PTCP was confirmed by a normal platelet count when examining citrated blood.
Awareness of typical PLT and WBC patterns may alert to the presence of EDTA-PTCP in routine laboratory practice helping to avoid unnecessary investigations and over-treatment.
KeywordsThrombocytopenia Laboratory hematology Hematology analyzers
Visual evaluation of blood smears is regarded as gold standard for detection of EDTA-PTCP, but only a limited amount of smears will be performed in routine laboratories. A simpler approach for detection of EDTA-PTCP is to inspect the histograms and flags of hematology analyzers. Although proper diagnostic accuracy studies have not been done and previous investigations using former models of hematology analyzer suggest some false-positive and false-negative results [1, 13], EDTA-PTCP is expected to be diagnosed correctly in most cases by this approach [8, 14]. In our practice, we visually evaluate blood smears in all cases with new or unexpected thrombocytopenia below 70 × 106/μl, and in cases with the typical histogram patterns or the respective flags of the hematology analyzer.
Which strategies can be then applied to determine the correct platelet count in daily practice? Several alternative anticoagulants have been investigated, but most of them are either not applicable to current hematology analyzers, or may induce pseudothrombocytopenia by themselves . In fact, besides EDTA, pseudothrombocytopenia was also recognised in samples anticoagulated with oxalate, heparin, and hirudin and even citrate [15, 16]. This in vitro phenomenon was not observed in samples anticoagulated with mixtures of EDTA and aminoglycosides [17, 18], with magnesium salt  and with the CPT mixture (citrate 17 mmol/l, pyridoxal 5′-phosphate 11.3 mmol/l and Tris 24.76 mmol/l) [8, 18, 20]. It is reported, that immediate processing of the blood samples and collection of the samples in pre-warmed tubes reduces the presence of platelet aggregates . However, this manoeuvre will be possible in special settings only. In our laboratory if platelet aggregates are found, we confirm EDTA-PTCP and assess the correct platelet count by obtaining a new sample using CPT as anticoagulant.
In conclusion, this case illustrates typical patterns of platelet and WBC histograms on automated hematology analyzers in EDTA-PTCP (Figure 1). Awareness of these patterns may alert to the presence of EDTA-PTCP in routine clinical practice. This may help physicians as well as laboratory personnel to be aware of EDTA-PTCP and to prevent unnecessary investigations as well as over-treatment.
Written informed consent was obtained from the patient for publication of this Case report and any accompanying images. A copy of the written consent is available for review by the Editor of this journal.
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