Reference values — Total calcium (serum)
Total serum calcium decreases in pregnancy due to hemodilution and lower albumin, while ionized calcium remains stable. Interpretation of low total calcium should always use albumin-corrected or ionized values.
| Units | Nonpregnant Adult | 1st Trimester | 2nd Trimester | 3rd Trimester |
|---|---|---|---|---|
| mg/dL | 8.7 – 10.2 | 8.8 – 10.6 | 8.2 – 9.0 | 8.2 – 9.7 |
| mmol/L | 2.18 – 2.55 | 2.20 – 2.65 | 2.05 – 2.25 | 2.05 – 2.43 |
Pregnancy-specific physiology
Total calcium falls during pregnancy because albumin decreases, but the biologically active ionized calcium remains normal. True hypocalcemia should therefore be confirmed with ionized calcium measurement.
Causes of elevated total calcium
- Primary hyperparathyroidism
- Malignancy (PTHrP-producing tumors or bone metastasis)
- Granulomatous disease (sarcoidosis, TB)
- Vitamin D intoxication
- Hyperthyroidism
- Adrenal insufficiency
- Immobilization
- Milk-alkali syndrome
- Thiazide diuretics
Causes of low total calcium
- Hypoalbuminemia (most common cause in pregnancy)
- Vitamin D deficiency
- Hypoparathyroidism
- Hypomagnesemia
- Renal insufficiency
- Pancreatitis
- Sepsis or critical illness
- Massive transfusion (citrate binding)
- Respiratory alkalosis
If symptoms occur, ionized calcium should be checked directly rather than relying on total calcium.
References
- Abbassi-Ghanavati M, Greer LG, Cunningham FG. Pregnancy and laboratory studies: a reference table for clinicians. Obstet Gynecol. 2009;114:1326–31.
- Wallach J. Interpretation of Diagnostic Tests. 8th ed. LWW; 2007.
- Fischbach FT, Dunning MB. Manual of Laboratory and Diagnostic Tests. 7th ed. LWW; 2004.