Relation between total and ionized serum calcium concentrations
- Alan S L Yu, MB, BChir
Alan S L Yu, MB, BChir
- Harry Statland and Solon Summerfield Professor of Medicine
- University of Kansas Medical Center
- Jason R Stubbs, MD
Jason R Stubbs, MD
- Associate Professor of Medicine
- Division of Nephrology & Hypertension
- University of Kansas Medical Center
- Section Editors
- Stanley Goldfarb, MD
Stanley Goldfarb, MD
- Editor-in-Chief — Nephrology
- Section Editor — Mineral and Bone Metabolism; Renal Ureteral Stones
- Professor of Medicine
- University of Pennsylvania School of Medicine
- Mitchell Geffner, MD
Mitchell Geffner, MD
- Section Editor — Pediatric Endocrinology
- Professor of Pediatrics
- Keck School of Medicine, University of Southern California
The plasma (or serum) calcium concentration is usually reported in units of mg/dL in the United States, in mmol/L in many other countries, and in meq/L by some laboratories. The relationship between these units is defined by the following equations:
mmol/L = [mg/dL x 10] ÷ mol wt
meq/L = mmol/L x valence
Since the molecular weight of calcium is 40 and the valence is +2, 1 mg/dL is equivalent to 0.25 mmol/L and 0.5 meq/L. Thus, the normal range of total serum calcium concentration of 8.8 to 10.3 mg/dL is equivalent to 2.2 to 2.6 mmol/L and 4.4 to 5.2 meq/L.
DETERMINANTS OF THE SERUM CALCIUM CONCENTRATION
The total serum calcium concentration consists of three fractions [1,2]:
- Moore EW. Ionized calcium in normal serum, ultrafiltrates, and whole blood determined by ion-exchange electrodes. J Clin Invest 1970; 49:318.
- Bushinsky DA, Monk RD. Electrolyte quintet: Calcium. Lancet 1998; 352:306.
- Ladenson JH, Lewis JW, Boyd JC. Failure of total calcium corrected for protein, albumin, and pH to correctly assess free calcium status. J Clin Endocrinol Metab 1978; 46:986.
- DENT CE. Some problems of hyperparathyroidism. Br Med J 1962; 2:1419.
- Mutlu EA, Keshavarzian A, Mutlu GM. Hyperalbuminemia and elevated transaminases associated with high-protein diet. Scand J Gastroenterol 2006; 41:759.
- Lindgärde F, Zettervall O. Hypercalcemia and normal ionized serum calcium in a case of myelomatosis. Ann Intern Med 1973; 78:396.
- Merlini G, Fitzpatrick LA, Siris ES, et al. A human myeloma immunoglobulin G binding four moles of calcium associated with asymptomatic hypercalcemia. J Clin Immunol 1984; 4:185.
- Pearce CJ, Hine TJ, Peek K. Hypercalcaemia due to calcium binding by a polymeric IgA kappa-paraprotein. Ann Clin Biochem 1991; 28 ( Pt 3):229.
- McCloskey EV, Galloway J, Morgan MA, Kanis JA. Pseudohyperphosphataemia in multiple myeloma. BMJ 1989; 299:1381.
- Oberleithner H, Greger R, Lang F. The effect of respiratory and metabolic acid-base changes on ionized calcium concentration: in vivo and in vitro experiments in man and rat. Eur J Clin Invest 1982; 12:451.
- Wang S, McDonnell EH, Sedor FA, Toffaletti JG. pH effects on measurements of ionized calcium and ionized magnesium in blood. Arch Pathol Lab Med 2002; 126:947.
- Krapf R, Jaeger P, Hulter HN. Chronic respiratory alkalosis induces renal PTH-resistance, hyperphosphatemia and hypocalcemia in humans. Kidney Int 1992; 42:727.
- Gauci C, Moranne O, Fouqueray B, et al. Pitfalls of measuring total blood calcium in patients with CKD. J Am Soc Nephrol 2008; 19:1592.
- Evenepoel P, Bammens B, Claes K, et al. Measuring total blood calcium displays a low sensitivity for the diagnosis of hypercalcemia in incident renal transplant recipients. Clin J Am Soc Nephrol 2010; 5:2085.
- Movilli E, Zani R, Carli O, et al. Direct effect of the correction of acidosis on plasma parathyroid hormone concentrations, calcium and phosphate in hemodialysis patients: a prospective study. Nephron 2001; 87:257.
- Kaye M, Somerville PJ, Lowe G, et al. Hypocalcemic tetany and metabolic alkalosis in a dialysis patient: an unusual event. Am J Kidney Dis 1997; 30:440.
- Ladenson JH, Lewis JW, McDonald JM, et al. Relationship of free and total calcium in hypercalcemic conditions. J Clin Endocrinol Metab 1979; 48:393.
- Nordenström E, Katzman P, Bergenfelz A. Biochemical diagnosis of primary hyperparathyroidism: Analysis of the sensitivity of total and ionized calcium in combination with PTH. Clin Biochem 2011; 44:849.
- Morton AR, Garland JS, Holden RM. Is the calcium correct? Measuring serum calcium in dialysis patients. Semin Dial 2010; 23:283.
- DETERMINANTS OF THE SERUM CALCIUM CONCENTRATION
- Change in total but not ionized calcium
- - Hypoalbuminemia
- - Hyperalbuminemia
- - Multiple myeloma
- Change in ionized fraction but not total calcium
- - Acid-base disorders
- - Parathyroid hormone
- - Hyperphosphatemia
- MEASURING THE SERUM CALCIUM IN PATIENTS WITH CKD