On the Cause and Degree of Intraindividual Serum Calcium Variability

Abstract

Intraindividual serum calcium variability (I.Ca.V.) has been examined under optimal sampling and analytical conditions in 12 normal persons in a standing and a recumbent position. Physiological protein fluctuations are mainly responsible for I.Ca.V. via their effect on protein-bound calcium. The I.Ca.V. remaining after correction for protein effects is of the same magnitude as directly measured ionized calcium variability=0.02 mmol/l. The individual normal range of serum calcium is four times narrower than the interindividual range, while variability of ionized calcium within and between individuals was identical. The effect of posture on normal range and intra-individual variability is emphasized.