[Evaluation of Payne's formula for the correction of calcium: comparison with improved calcium and albumin measurement methods].

The ionized or free fraction of serum calcium is physiologically important for cellular function, but we most often measure total serum calcium. There are a number of correction formulas that can be used to estimate whether low total serum calcium can be attributed simply to low albumin or serum protein. In Japan, Payne's formula has been widely used to correct calcium concentration.