The Ultrafiltrable Calcium of Human Serum. Ii. Variations in Disease States and Under Experimental Conditions1

The total serum calcium is composed of two ma-jor fractions: the non-diffusible or protein bound calcium, and the diffusible or ultrafiltrable cal-cium. The latter, containing predominantly ionic calcium, theoretically traverses capillary mem-branes in vivo and participates in metabolic proc-esses at the cellular level. In a previous publication, a new simple method for the ultrafiltration of human serum was de-scribed (1). It was found that in normal adults, between 60 and 70 per cent of the calcium present in serum was ultrafiltrable. These findings were compared with the variable values reported by other authors for the normal percentage of ultra-filtrable calcium. It was pointed out that virtually all previous workers had failed to control both the pH and the temperature during their ultrafiltra-tion procedures. Our data indicated that these variables had a considerable effect on the ultra-filtrability of serum calcium, thus offering an ex-planation for the lack of agreement, particularly among the early workers (2), in the study of nor-mal and abnormal sera. Only the recent data of Hopkins, Connor, and Howard (3) show reason-able consistency for specific disease states. They used the Lavietes mercury-pressure ultrafiltration apparatus, controlled pH, and carried out the ul-trafiltration procedure at room temperature. Utilizing the controlled technique previously described (1) we have reinvestigated the distri-bution of calcium in the serum of a group of pa-tients with hypercalcemia and hypocalcemia. These results are given in the first portion of this communication. Although differing in the abso-lute quantity, and therefore the per cent of ultra-filtrable calcium, our findings are in agreement with those reported by Hopkins and her associates