Bone & calcium
Calcium (total / ionized)
Tightly regulated by PTH and vitamin D; correct total Ca for albumin or measure ionized.
Sample
Serum
Clinical reference range
8.5 to 10.5 mg/dL
Total
Conv: 8.5–10.5 mg/dL
Biology
What it measures
Regulated by PTH (raises), calcitriol (raises), and calcitonin (lowers).
Clinical use
Why we order it
Hyperparathyroidism, malignancy of bone, vitamin D status.
Differential
Causes of abnormal values
Causes of HIGH
- ↑Primary hyperparathyroidism
- ↑Malignancy (PTHrP, lytic, vitamin D)
- ↑Granulomatous disease
- ↑Thiazides
- ↑Lithium
- ↑Familial hypocalciuric hypercalcemia
Causes of LOW
- ↓Hypoparathyroidism
- ↓Vitamin D deficiency
- ↓CKD (with high phosphate)
- ↓Acute pancreatitis
- ↓Hypomagnesemia
Pitfalls
Pre-analytic & interpretation traps
- !Corrected Ca = measured + 0.8 × (4 − albumin g/dL); ionized is preferred in critical illness.
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