Correlation and Dissociation Factors between Ionized, Total, and Corrected Calcium in Patients Undergoing Hemodialysis

Abstract Ionized calcium (iCa) is physiologically active but cannot be directly measured easily. Although total serum calcium (tCa) and corrected calcium (cCa) using the Payne correction formula have been utilized to assess calcium levels, their limitations have been pointed out. This study aimed to clarify the degree of correlation and dissociation among iCa, tCa, and cCa levels in patients undergoing hemodialysis. A cross-sectional study assessed the correlation between iCa, tCa, and cCa levels. Factors involved in the correlation between the iCa and tCa levels were evaluated using multiple regression analysis. Two hundred thirteen patients were enrolled. Patients were 65 ± 10.2 years old. The correlation coefficients were 0.8665 for iCa and tCa and 0.8537 for iCa and cCa. Correlations were also observed when divided by albumin concentration and pH, known correlation factors. In multiple regression analysis of the relationship between tCa and iCa, albumin, pH, phosphorus, and magnesium levels were significant factors. Based on these results, a new corrected calcium equation (mg/dL) = 0.828 × tCa − 0.314 × albumin (g/dL) + 0.007 × age + 2.922 was derived using age and albumin. There was a correlation between iCa, tCa, and cCa in hemodialysis patients.