Spurious hyperkalaemia due to EDTA contamination: common and not always easy to identify.

BACKGROUND

To study the detection and prevalence of spurious hyperkalaemia due to potassium ethylenediaminetetra-acetic acid (kEDTA) contamination.

METHODS

In a one-month prospective study, serum EDTA, zinc, calcium, magnesium concentrations and alkaline phosphatase activity were measured in samples with serum potassium >or=6.0 mmol/L.

RESULTS

Twenty-eight out of 117 hyperkalaemic samples were contaminated with EDTA. Only serum zinc values below the reference range had 100% sensitivity for indicating EDTA contamination, but even at an optimal specificity of 89% at least 12 potentially genuine hyperkalaemic samples would be rejected.

CONCLUSION

Spurious hyperkalaemia due to kEDTA contamination is common. Gross kEDTA contamination is obvious by marked unexpected hyperkalaemia, hypocalcaemia, hypomagnesaemia and hypozincaemia. Spurious hyperkalaemia due to low concentrations of kEDTA contamination can only be confidently detected by measurement of serum EDTA.