Calcium
Primary mineral for bone health, muscle contraction, and nerve conduction
Also known as
Definition
Calcium is the most abundant mineral in the human body (approximately 1 kg), with 99% stored in bones and teeth. The remaining 1% in the blood regulates muscle contraction, heart rhythm, nerve impulse conduction, blood clotting, and hormone secretion. Serum levels are tightly regulated by PTH, calcitriol (active vitamin D), and calcitonin. Albumin must be considered when interpreting results — ionized calcium is more reliable.
| Parameter | Value |
|---|---|
| Unit | mmol/l (mg/dl) |
| Reference Range | 2.12–2.62 mmol/l (8.5–10.5 mg/dl) total calcium; ionized Ca: 1.15–1.35 mmol/l |
Agree on your personal target range with your doctor.
Conversion: 1 mmol/l = 4.01 mg/dl. US labs report in mg/dl (normal 8.5–10.5 mg/dl).
↓ What a low value means
Hypocalcemia (< 2.12 mmol/l) occurs in hypoparathyroidism, vitamin D deficiency, magnesium deficiency, malabsorption, or renal insufficiency. Symptoms: muscle cramps (tetany), tingling, Chvostek's sign, cardiac arrhythmias; severe deficiency can cause laryngospasm. Apply the albumin correction formula.
↑ What a high value means
Hypercalcemia (> 2.62 mmol/l) is most commonly caused by primary hyperparathyroidism or malignancies (90% of cases). Symptoms: 'Bones, Stones, Groans, Thrones' — bone pain, nephrolithiasis, abdominal pain, polyuria, altered consciousness. Above 3.0 mmol/l it is a medical emergency.
✓ What can influence this value
The calcium value is influenced by calcium intake from dairy products, fortified plant-based beverages, legumes, kale, broccoli, and sardines, by vitamin D status (vitamin D promotes calcium absorption in the gut), parathyroid hormone, kidney function, and the albumin level. Calcium-containing preparations, thiazide diuretics, and a prolonged tourniquet time on the arm during the blood draw can change the measured result.
When to test
For osteoporosis screening, kidney stones, muscle cramps, suspected hyperparathyroidism, malignancy monitoring, or regularly in CKD and hyperparathyroidism. Ionized calcium is preferred over total calcium when albumin is abnormal.
Frequently asked questions
Is calcium supplementation dangerous for the heart? +
Some observational studies showed increased cardiovascular risk with high-dose calcium supplementation (> 1,000 mg/day), particularly as calcium carbonate. Dietary calcium intake is safer. When supplementing, combine with vitamin K2 and magnesium, which guide calcium into bones and reduce vascular calcification.
Why does calcium need to be corrected for albumin? +
About 40% of blood calcium is bound to albumin. With low albumin (e.g., malnutrition or liver disease), total calcium appears falsely low even though active ionized calcium is normal. Correction formula: corrected Ca = measured Ca + 0.02 × (40 − albumin in g/l).
How are vitamin D and calcium linked? +
Calcitriol (active vitamin D / 1,25(OH)2D3) increases intestinal calcium absorption from approximately 10–15% without vitamin D to 30–40% with adequate supply. Vitamin D deficiency secondarily leads to low calcium and a compensatory rise in PTH (secondary hyperparathyroidism) with bone resorption.
Calcium
Sources
Last updated: May 28, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.