Serum ionized calcium during bed rest in fracture patients and normal men

Abstract

Nine of ten patients immobilized for the treatment of tractures were found to have abnormal elevations of serum ionized calcium when determined with an ion-sensitive electrode, while only three of the ten had hypercalcemic values ( 10.2, 10.4, and 11.7 mg 100 ml ) by atomic absorption spectroscopy (normal range, 8.2–10.1 mg 100 ml ). Mean serum ionized calcium values were 5.3–7.2 mg 100 ml in seven of the patients ( normal range, 4.5–5.2 mg 100 ml ), and two others had normal mean values but some individual abnormal measurements. Because of these observations, daily measurements of serum total and ionized calcium, and urinary calcium were made on four normal volunteers before, during, and after a 12-day bed rest period. Abnormal elevations of serum ionized calcium occurred during bed rest in all four subjects (peaks, 5.7–5.9 mg 100 ml ), while serum total calcium remained normal. Elevations of urinary calcium occurred in all four, but no clear temporal relation with the serum ionized calcium was seen. It is concluded that bed rest produces early and significant elevations of the serum ionized calcium, while there are minimal changes in the serum total calcium. The pathogenesis of these changes remains obscure.