Hemolysis Interference Studies: The Particular Case of Sodium Ion

BACKGROUND: Despite many studies assessing hemolysis interference in almost every clinically relevant magnitude, sodium has poorly been assessed. Our aim was to evaluate hemolysis interference on plasma sodium, using different strategies of hemolysis preparation, at different baseline sodium ion concentrations and bias specifications. METHODS: Two different strategies were used for the preparation of hemolysis from lithium heparin blood samples. Repeatibility was calculated at two levels for each strategy and interferograms were outlined for both approaches at sodium concentrations between 130-145 mmol/L. Results were interpreted according to different specifications: reference change value, RiLiBAK, Westgard’s database, RCPA-QAP and CLIA. RESULTS: The coefficients of variation of the hemolyzed samples using the first strategy were lower than for the second strategy (0.23-0.78% vs 0.57-48.6%, for 0.2 g/dL free Hb and 0.28-0.44% vs 0.40-135.1%, for 0.9 g/dL free Hb). Statistically significant differences were seen when comparing the slopes of the pairs of interferograms at each sodium concentration obtained by both strategies (p<0.001 for 130 mmol/L; p=0.068 for 135 mmol/L; p=0.002 for 140 mmol/L and p=0.001 for 145 mmol/L). Hemolysis cut-off values were generally independent of the sodium concentration. CONCLUSIONS: Reproducibility of hemolysate preparation is procedure-dependent. A greater standardization is needed for the preparation of a true hemolysate to better quantify the degree of interference of clinically relevant analytes, especially those with higher complexity such as sodium. We found a concentration-independent cut-off value for the hemolysis index that allows the establishment of a single and robust value in every laboratory, according to their quality specifications.