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Am J Clin Pathol. 2011 Oct;136(4):646-52.
Amikacin can be added to blood to reduce the fall in platelet count.
Zhou X, Wu X, Deng W, Li J, Luo W.
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Clin Chem Lab Med. 2012 Mar 3;50(8):1387-91.
Novel method to dissociate platelet clumps in EDTA-dependent pseudothrombocytopenia based on the pathophysiological mechanism.
Chae H, Kim M, Lim J, Oh EJ, Kim Y, Han K.
Department of Laboratory Medicine, College of Medicine, The Catholic University of Korea, Seoul, South Korea.
BACKGROUND: EDTA-dependent pseudothrombocytopenia (EDTA-PTCP) is an in vitro phenomenon of platelet clumping that leads to spuriously low platelet counts by automatic hematology analyzers. The mechanism is not clearly defined, but is known as an immunologically mediated phenomenon due to the presence of EDTA-dependent antiplatelet auto-antibodies that induce platelet clumping. The purpose of this study was to identify antiplatelet antibodies in EDTA-PTCP samples and to design a method to dissociate platelet clumps based on the pathophysiological mechanism.
METHODS: The antiplatelet antibody was investigated using direct and indirect immunofluorescent flow cytometric methods in 23 EDTA-anticoagulated whole blood (WB) samples and 12 serum samples of EDTA-PTCP patients, respectively. A novel mixture containing 9 mmol/L CaCl(2) and 0.1 unit/L sodium heparin, that provides calcium replacement while curbing coagulation, was designed to dissociate platelet clumps. The effect on dissociation was demonstrated in 26 samples of EDTA-PTCP and compared with the established method of kanamycin supplementation.
RESULTS: The direct test was positive for IgM and IgG antiplatelet antibody in 60.9% and 4.4% of patients, respectively [mean median fluorescence intensity (MFI) of 223.9 and 128.4, respectively]. The indirect test was positive for IgM antiplatelet antibody in 58.3% of patients (mean MFI of 123.4). The novel method dissociated the platelet clumps with a mean increased platelet count of 242.3% and was equivalent in efficiency to kanamycin supplementation.
CONCLUSIONS: The novel method is an easily applicable and efficient measure that allows dissociation of platelet clumps, based on the pathophysiological mechanism of EDTA-PTCP.
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Clin Chem Lab Med. 2012 Aug;50(8):1281-5.
EDTA-dependent pseudothrombocytopenia: further insights and recommendations for prevention of a clinically threatening artifact.
Lippi G, Plebani M.
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 <100×10(9)/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.