Diagnostic approach to hypocalcemia
- David Goltzman, MD
David Goltzman, MD
- Professor of Medicine
- McGill University
- Senior Physician, Division of Endocrinology and Department of Medicine
- McGill University Health Centre
Hypocalcemia has many causes (table 1). It can result from inadequate parathyroid hormone (PTH) secretion, PTH resistance, vitamin D deficiency or resistance, abnormal magnesium metabolism, and extravascular deposition of calcium, which can occur in several clinical situations. (See "Etiology of hypocalcemia in adults" and "Etiology of hypocalcemia in infants and children".)
The diagnostic approach to hypocalcemia involves confirming, by repeat measurement, the presence of hypocalcemia and distinguishing among the potential etiologies. The diagnosis may be obvious from the patient's history; examples include chronic kidney disease and postsurgical hypoparathyroidism. When the cause is not obvious or a suspected cause needs to be confirmed, other biochemical tests are indicated.
This topic will review the evaluation of patients with hypocalcemia. The clinical manifestations and treatment of hypocalcemia are discussed separately. (See "Clinical manifestations of hypocalcemia" and "Treatment of hypocalcemia".)
The first step in the evaluation of a patient with hypocalcemia is to verify with repeat measurement (total serum calcium corrected for albumin or ionized calcium) that there is a true decrease in the serum calcium concentration. If available, previous values for serum calcium should also be reviewed. If the patient has a low albumin-corrected serum calcium or ionized calcium concentration, further evaluation to identify the cause is indicated. (See 'Determining the etiology' below.)
Hypoalbuminemia: Calcium correction — Calcium in serum is bound to proteins, principally albumin. As a result, the total serum calcium concentration in patients with low or high serum albumin levels may not accurately reflect the physiologically important ionized (or free) calcium concentration. Each 1 g/dL reduction in the serum albumin concentration will lower the total calcium concentration by approximately 0.8 mg/dL (0.2 mmol/L) without affecting the ionized calcium concentration and, therefore, without producing any symptoms or signs of hypocalcemia.To continue reading this article, you must log in with your personal, hospital, or group practice subscription. For more information on subscription options, click below on the option that best describes you:
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- CONFIRM HYPOCALCEMIA
- Hypoalbuminemia: Calcium correction
- Ionized calcium
- DETERMINING THE ETIOLOGY
- Clinical clues
- Laboratory evaluation
- - Serum PTH concentrations
- - Magnesium
- - Phosphate
- - Vitamin D metabolites
- - Patterns of vitamin D metabolites and phosphate
- - Other
- INFORMATION FOR PATIENTS
- SUMMARY AND RECOMMENDATIONS