Influence of posture on the serum concentration of calcium

Abstract

Experiments were designed to study the effects of change in posture on the serum concentrations of total calcium, plasma ionic calcium, magnesium, protein-bound calcium, total protein, albumin, and globulin. Plasma ionic calcium and serum magnesium were not influenced by changes in posture. All the remaining constituents responded in a consistent manner, namely, on changing from the lying to the erect position, their concentrations rose significantly. On sitting or on lying down, their values fell reaching minimal levels after about 1 2 hr and showing little change thereafter. All the values attained on lying were significantly lower than those reached on sitting in the same time periods. Variations in the concentrations of calcium and protein due to alteration in posture could amount to as much as 47% and 71%, respectively, of their normal range spans. These variations were considerably reduced by the use of protein corrections developed by Dent and in particular by Parfitt. A sex difference was noted in the concentrations of both serum total calcium and total protein, more marked in the latter. The difference in calcium appears due to a difference in its protein-bound component. It is clear that the influence of posture must be considered when interpreting serum calcium concentrations. Failure to recognize this influence has undoubtedly contributed to the variations in the normal ranges of serum calcium proposed by different workers.