Measure of blood ionized calcium versus total calcium in normal man, in renal insufficiency and in hypercalcemia of various origins

Abstract

Ca⁺⁺ and Ca tot were measured and compared at 2 years interval (S1 and S2) in 45 normal volunteers: 26 females and 19 males age 20/65 years. ForCa⁺⁺ the mean difference between S1 and S2 was small (0.009 mmol/1) but significant (p < 0.01). For Ca tot the mean difference between S1 and S2 (0.06 mmol/1) was very significant (p < 0.001) due to the combination of various factors: technical, sex difference and proteins. In both series (S1 + S2) Ca⁺⁺ did not differ significantly between females and males, whereas Ca tot was significantly (p < 0.05) higher in males (mean difference 0.06 mmol/1) for S1 and non significant for S2.

In 63 normal volunteers we cross correlated the factors of calcium homeostasis and showed significant relationship between Ca⁺⁺/Ca tot r = 0.428 (p < 0.001), Ca⁺⁺/PTH r = -0.297 (p < 0.05), Ca tot/Proteins r = 0.518 (p < 0.001). The relationship between Ca tot and PTH does not reach the level of significance.

We compared Ca⁺⁺ and Ca tot in renal insufficiency (RI) (n = 16), hyperparathyroidism surgically confirmed (Hyper P) (n = 10), cancer with hypercalcemia (C) (n = 9) and in normal volunteers (N) (n = 63). The relationship between Ca⁺⁺ and Ca tot in the pathologic groups has significantly steeper slopes than the control group (N), p < 0.05 for RI and C and p < 0.01 for Hyper P. The increase of the Ca⁺⁺/Ca tot ration in RI and Hyper P is positively correlated to PTH levels, nor albumin variations neither pH and P04 variations could completely account for the increase of the ratio. The increase of Ca⁺⁺/Ca tot in cancer is independent of PTH and cannot entirely be explained by the albumin drop.