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. The albumin level affects interpretation; ionized calcium is more reliable here.
| 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. With low albumin, the value is interpreted using a correction formula.
↑ What a high value means
Hypercalcemia (> 2.62 mmol/l) is most commonly caused by primary hyperparathyroidism or malignancy; in adults with hypercalcemia these two causes together account for about 90% of cases, with hyperparathyroidism predominating in outpatients and malignancy in hospitalized patients. Symptoms: 'Bones, Stones, Groans, Thrones' — bone pain, nephrolithiasis, abdominal pain, polyuria, altered consciousness. According to the Society for Endocrinology's acute guidance (2016), calcium above 3.5 mmol/l requires urgent correction because of the risk of heart rhythm disturbances and coma; such a value needs immediate medical assessment, even without symptoms. At 3.0 to 3.5 mmol/l, prompt treatment is usually indicated. Altered consciousness is an emergency; calling your local emergency number is then the right step.
✓ 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
Calcium is measured in osteoporosis evaluation, kidney stones, muscle cramps, suspected hyperparathyroidism (overactive parathyroid glands) and in cancer; in chronic kidney disease (CKD) and known hyperparathyroidism also over time. How often it is measured is decided by your doctor. Ionized calcium is more informative than 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, particularly as calcium carbonate. Whether and how to supplement is decided by your doctor.
Why is calcium 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.