Factitiously high sodium activities on the Ektachem 400 owing to interferences by high gamma-globulin concentrations.

Sera from patients with above-normal gamma-globulin concentrations give sodium values as much as 10% higher when measured in the Kodak Ektachem 400 analyzer than results obtained with the Beckman Astra-8 analyzer. Results obtained with the Astra were in agreement with flame photometry. A similar relative bias was observed for potassium measurement in the Ektachem. This discrepancy was corrected when we used a new generation of reference fluid provided by Kodak, which is currently available for general use.