Reference ranges for free calcium in venous serum

Abstract

After obtaining an informed consent, venous blood samples were taken in gel tubes without additives from 125 healthy blood donors for analysis of free calcium in serum. In addition, pH was measured, and free calcium standardized to pH 7.40 calculated. In a subgroup, venous blood samples were also taken to measure the same analytes in serum from gel tubes with thrombin (n = 35) and in venous blood from Radiometer safePICO-aspirator with 80 IU electrolyte balanced, dry heparin (n = 31). Reference ranges in venous serum were estimated to 1.17-1.32 mmol/L for free calcium, and to 1.19-1.33 mmol/L for free calcium standardized to pH 7.40. Median free calcium was 0.03 mmol/L higher in serum than in blood, and median free calcium standardized to pH 7.40 was 0.04 mmol/L higher in serum. The difference between the two serum types was small (0.01 mmol/L).

Keywords

• free calcium
• ionized calcium
• sample material
• reference ranges
• free calcium standardized to ph 7.40
• venous blood gas analyses