Role of Correction Factor in Minimizing Errors While Calculating Electrolyte Values between Blood-gas Analyzer and Laboratory Autoanalyzer: A Comparative Study.

AIMS

Electrolytes are charged elements that play important functions in the body. They are measured by both arterial blood-gas (ABG) analyzers and autoanalyzers (AA). In this study, we tried to find out the correction factor for sodium and potassium to establish the concordance between ABG and AA values.

MATERIALS AND METHODS

We prospectively studied 100 samples of patients, and for validation of the result, we applied our result on 30 patients later. 1.5 ml of blood collected in the 2.0 ml syringe preflushed with heparin and analyzed using blood-gas analyzer (ABG). Another sample was sent, to central laboratory, where serum Na+ and K+ concentrations were analyzed. Means, standard deviations, and coefficients of variation with Karl Pearson's correlation coefficients were found out. Deming regression analysis was performed and Bland-Altman plots were also constructed.

RESULTS

The mean sodium and potassium were 130.27 ± 7.85 mmol/L and 3.542 ± 0.76 mmol/L using ABG and 139.28 ± 7.89 mmol/L and 4.196 ± 0.72 mmol/L using AA. Concordance between ABG and AA is done by adding the correction factor: for sodium, correction factor is 9.01, standard error = 1.113, class interval = 6.815-11.205; and for potassium (K+), correction factor is 0.654, standard error = 0.1047, class interval = 0.4475-0.8605.

CONCLUSION

The instrument type and calibration methods differ in different hospitals, so it is important that each center conducts an in-hospital study to know the correction factor before installation of an ABG, and the factor should be used accordingly to minimize all errors.