Contamination of lithium heparin blood by K2-ethylenediaminetetraacetic acid (EDTA): an experimental evaluation

INTRODUCTION: The contamination of serum or lithium heparin blood with ethylenediaminetetraacetic acid (EDTA) salts may affect accuracy of some critical analytes and jeopardize patient safety. The aim of this study was to evaluate the effect of lithium heparin sample contamination with different amounts of K(2)EDTA. MATERIALS AND METHODS: Fifteen volunteers were enrolled among the laboratory staff. Two lithium heparin tubes and one K(2)EDTA tube were collected from each subject. The lithium-heparin tubes of each subject were pooled and divided in 5 aliquots. The whole blood of K(2)EDTA tube was then added in scalar amount to autologous heparinised aliquots, to obtained different degrees of K(2)EDTA blood volume contamination (0%; 5%; 13%; 29%; 43%). The following clinical chemistry parameters were then measured in centrifuged aliquots: alanine aminotranspherase (ALT), bilirubin (total), calcium, chloride, creatinine, iron, lactate dehydrogenase (LD), lipase, magnesium, phosphate, potassium, sodium. RESULTS: A significant variation starting from 5% K(2)EDTA contamination was observed for calcium, chloride, iron, LD, magnesium (all decreased) and potassium (increased). The variation of phosphate and sodium (both increased) was significant after 13% and 29% K(2)EDTA contamination, respectively. The values of ALT, bilirubin, creatinine and lipase remained unchanged up to 43% K(2)EDTA contamination. When variations were compared with desirable quality specifications, the bias was significant for calcium, chloride, LD, magnesium and potassium (from 5% K(2)EDTA contamination), sodium, phosphate and iron (from 29% K(2)EDTA contamination). CONCLUSIONS: The concentration of calcium, magnesium, potassium, chloride and LD appears to be dramatically biased by even modest K(2)EDTA contamination (i.e., 5%). The values of iron, phosphate, and sodium are still reliable up to 29% K(2)EDTA contamination, whereas ALT, bilirubin, creatinine and lipase appear overall less vulnerable towards K(2)EDTA contamination.