[Total calcium or ionized calcium? A comparative study].

Determining ionized calcium after CO2 equilibration of serum with subsequent electronic conversion to pH 7.40 (Ca2+corr) gives a practicable value for the diagnosis of calcium metabolism. "Anaerobic" sampling, necessary for the measurement of the actual calcium ion concentration, is obviated. Protein or albumin concentration in serum and complex-bound calcium do not interfere. Comparison of sera from 54 patients with bone metastases or myeloma, as well as from 300 patients with other diseases, indicate that the sensitivity of Ca2+corr in the diagnosis of hypercalcaemia is about twice or three times that of total calcium and that the latter's specificity - at least when ignoring protein concentration - is unsatisfactory with 18-45% "falsely" reduced values.