EFFECT OF PHOSPHATE (P) CONCENTRATION ON IONIZED CALCIUM (iCa) CONCENTRATION IN VITRO

Abstract

From previous studies measuring ultrafilterable Ca, it was felt that increasing P concentration would lead to a decrease in iCa, due to P binding to iCa. Since no specific studies measured directly iCa as a function of P, we examined the effect of P on iCa concentration in vitro. We hypothesized that within the range of clinically encountered pH an increase in serum P would lead to a decrease in iCa. A single donor serum was aliquoted into 25 samples stored in CO₂ sealed tubes, and divided into 5 subsets of 5 tubes. pH was altered in 4 of the 5 subsets by adding various concentration of HCL or of NaOH. The pH's studied were: 7.09, 7.28, 7.35, 7.51, and 7.63. P concentration was altered in each subset by adding various concentrations of a P buffer with a pH of 7.4. The P concentrations studied were 2.5, 4.6, 6.8, 8.3, 11.1 mg/dl. iCa was measured using a Radiometer iCa 1 ion-selective electrode (standard error of measurement: 0.04 mg/dl). There was an inverse relationship between iCa and P which was similar at all pH's studied (r ranging from -0.84 to -0.94, p<0.001). The slopes did not differ significantly from each other, indicating no deviation from parallelism of these 5 regression lines. iCa concentration correlated inversely with pH (p<0.001). There was no significant interaction between P concentration and pH. Therefore iCa concentration in vitro inversely correlates with pH and P concentration. We suggest that in addition to factors well known to influence iCa concentration (such as protein, bicarbonate and pH), serum P concentration also plays a significant role.

Log in or create a free account to read this content

Gain free access to this article, as well as selected content from this journal and more on nature.com

Access through your institution

or

Sign in or create an account

Continue with Google

Continue with ORCiD