Objective: The present study examines the effect of hemolysis on serum sodium concentrations in hyponatremic and hypernatremic serum samples.

Material and Methods: Samples were assessed by three different sodium methods; direct ISE by means of dry chemistry (Vitros 250), direct ISE (Medica Easylyte), and indirect ISE (Olympus AU 5223) methods. We prepared fresh serum pool and further distilled water and 20% NaCl solutions were included respectively to achieve hyponatremic and hypernatremic concentrations. The CV values of the analyzers were 0.34%, 0.32%, 0.47% in hyponatremic samples and 0.24%, 0.29%, 0.60% in hypernatremic samples respectively. We added hemolysates into the samples to give hemoglobin concentrations of 305-1150 mg/dl. Samples were studied three times and the arithmetic means were calculated.

Results: In hyponatremic samples, hemolytic interference was not significant. Similarly, in hypernatremic samples assayed with Vitros 250 autoanalyzer and Medica analyzer the hemolytic interference was not significant. In 4+ and 5+ hemolyzed hypernatremic serum samples assessed with Olympus AU 5223 autoanalyzer, the negative deviations were over the E_A for sodium (E_A for Na = 4.0 mmol/L, CLIA ‘88).

Conclusion: The performance of analyzers using direct ISE method was better than the ones using indirect ISE method in hypernatremic hemolyzed serum samples. Because the analyzers using direct ISE revealed better analytical performances than indirect ISE methods in serum sodium assessments on hemolyzed samples, it will be helpful in method decision.