Potassium EDTA Contamination Causing Preanalytical Errors in Canine and Feline Serum Samples

BACKGROUND: Contamination of serum samples with the anticoagulant potassium ethylenediaminetetraacetic acid (kEDTA) constitutes a critical pre-analytical error in veterinary diagnostics and can lead to potentially life-threatening misinterpretation of biochemical test results. OBJECTIVES: To develop and validate a method for quantifying EDTA in canine and feline sera. A second aim was to evaluate the effect and prevalence of kEDTA contamination in canine and feline serum samples. METHODS: A copper-PAN-based automated method for quantifying EDTA in canine and feline sera was developed. Canine and feline serum samples admitted together with EDTA tubes were analyzed for kEDTA contamination. RESULTS: The measuring range was set to 0.03-0.4 mM, with a coefficient of variation of < 13.1% and acceptable linearity upon dilution (75%-118%). Spiking experiments demonstrated that kEDTA caused a dose-dependent increase in potassium and decreases in calcium, magnesium, iron, and zinc, with iron and zinc most profoundly affected. The allowable total error was exceeded at low kEDTA concentrations, even when analytes remained within reference intervals. A prevalence study of 1065 serum samples submitted with kEDTA tubes revealed contamination rates of 1.1% in dogs and 1.8% in cats. CONCLUSIONS: These findings emphasize that even small amounts of kEDTA can compromise diagnostic accuracy. This underscores the importance of strict compliance with recommended blood collection order and highlights the value of direct EDTA measurements in veterinary laboratory diagnostics.