Calcium Disorders: Hyper- and Hypocalcemia Profiles
Total calcium must be corrected for albumin before interpretation.
Correction
For every 1 g/dL the albumin is below 4.0 g/dL, add ~0.8 mg/dL to the measured total calcium. In critical illness, ionized calcium is preferred.
Hypercalcemia
- Most common outpatients: primary hyperparathyroidism (high or inappropriately normal PTH with high calcium).
- Most common inpatients: malignancy (PTHrP, bone disease) — suppressed PTH.
- Other: vitamin D/calcium excess, thiazides, immobilization, sarcoidosis (related to excess calcitriol), thyrotoxicosis.
- Severe (> 14 mg/dL or < 12 mg/dL with symptoms) is an emergency.
Hypocalcemia
- Causes: hypoalbuminemia (corrected value usually normal), chronic kidney disease (low calcitriol, hyperphosphatemia), hypoparathyroidism, vitamin D deficiency, magnesium deficiency, pancreatitis (calcium deposition).
- With a low PTH: hypoparathyroidism; with a high PTH: a target-organ disorder (vitamin D, Mg, kidney) should be sought.
Key checks
Fasting sample, albumin, phosphate, magnesium, PTH, vitamin D (25-OH and 1,25-OH), and renal function together classify the disorder.