Clinically Reviewed by Dr. Andrew Stein MD, Consultant Physician. Last updated: April 2026
Calcium is perhaps the most famous mineral in the body, known primarily for building strong bones and teeth.
However, its role in the blood is even more critical: it acts as a vital signaling molecule that allows your heart to squeeze, your blood to clot, and your nerves to send electrical impulses.
Because even slight deviations can disrupt the heart and brain, your body uses the parathyroid glands (four tiny glands in your neck) to monitor and maintain calcium levels with extreme precision.
For most healthy adults, a normal total blood calcium level is between 2.2 and 2.6 mmol/L (or 8.5 to 10.5 mg/dL).
Note: About half of the calcium in your blood is “active” (ionised), while the other half is bound to proteins like albumin. Doctors often look at “Adjusted Calcium” to account for your protein levels. Always check the reference range on your specific lab report.
Calcium imbalances are categorised into two conditions. Both can have significant effects on your “excitable” tissues, like muscles and nerves.
| Condition | Level | Definition |
| Hypocalcaemia | Below 2.2 mmol/L | Low blood calcium |
| Hypercalcaemia | Above 2.6 mmol/L | High blood calcium |
Calcium acts as a gatekeeper for electrical signals.
High calcium acts like a sedative; it makes it harder for nerves to fire, leading to sluggishness and muscle weakness.
Low calcium makes nerves “hyperexcitable”; they fire too easily, leading to twitches, cramps, and tingling.
Hypercalcaemia is often discovered during routine blood tests, sometimes before a patient feels any symptoms.
Hyperparathyroidism: The most common cause. One or more of the parathyroid glands becomes overactive and “pumps” too much calcium into the blood.
Malignancy: Certain types of cancer (including myeloma) can release calcium from the bones into the bloodstream.
Vitamin D Toxicity: Excessive intake of Vitamin D supplements can cause the gut to absorb too much calcium.
Medications: Thiazide diuretics (like bendroflumethazide or indapamide, used for high blood pressure) can reduce the amount of calcium the kidneys excrete.
Hypocalcaemia often indicates an issue with the body’s “supply chain” or the hormones that move calcium into the blood.
Vitamin D Deficiency: Without enough Vitamin D, the body cannot absorb calcium from food effectively.
Hypoparathyroidism: If the parathyroid glands are damaged (sometimes during neck surgery), they won’t produce the hormone needed to maintain levels.
Chronic Kidney Disease (CKD: Failing kidneys cannot activate Vitamin D, and they may also lose too much calcium in the urine.
Magnesium Imbalance: Very low magnesium levels can “paralyze” the parathyroid glands, preventing them from releasing calcium.
Treatment focuses on the “Three M’s”: Movement, Metabolism, and Management of the underlying cause.
For High Calcium: The immediate goal is “flushing” the system. Patients are given intravenous (IV) fluids to help the kidneys pee out the excess. In more severe cases, medications like bisphosphonates are used to stop bones from releasing more calcium.
For Low Calcium: Treatment usually involves oral calcium carbonate or citrate tablets. If Vitamin D is the culprit, high-dose supplements are prescribed. In emergency cases (where a patient has muscle spasms), calcium is given via an IV drip.
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