Rapid method for determining ultrafiltrable calcium in serum.

Methods for determining ultrafiltrable calcium in serum (UFCa) are comprehensive and time-consuming because pH must be strictly controlled, either by anaerobic technique throughout the process or by saturating the sera with C02-02 mixtures. Farese et al. (1) reported a simple method for separating diffusible calcium in serum by centrifugation through high-flux ultrafiltration membranes. Anaerobically sampled serum was centrifuged under oil through the membrane for 30 mm, which yielded about 2 ml of ultrafiltrate. The authors did not consider the influence on UFCa of pH changes before or during ultrafiltration, or the influence of temperature on protein-bound calcium-questions dealt with in the present report. A modification of the procedure is