Calcium
A mineral vital for bones, nerves, and muscle. Blood calcium is tightly controlled and reflects bone and parathyroid health.
Typical reference range
| Range | Unit |
|---|---|
| 2.15–2.51 | mmol/l |
What Calcium measures
Serum calcium measures the calcium circulating in your blood. Calcium is a tightly regulated mineral that does far more than build bones: it helps nerves fire, muscles contract, and blood clot normally. The body keeps blood levels within a narrow band using parathyroid hormone (PTH) and vitamin D, which together adjust how much calcium is absorbed from food, released from bone, and held onto by the kidneys. About half of the calcium in blood is bound to the protein albumin, so when albumin is abnormal, a result may be corrected for albumin to better reflect the active portion. Because of this, calcium is rarely read alone. A clinician usually interprets it alongside PTH, vitamin D, phosphate, and albumin.
What a high Calcium can mean
A high calcium level (hypercalcemia) can suggest that too much calcium is entering the blood or too little is being cleared. The most common cause is overactive parathyroid glands (primary hyperparathyroidism), where excess PTH pulls calcium from bone. Other causes commonly associated with a raised level include certain cancers (malignancy), excess vitamin D or over-supplementation, and some medications such as thiazide diuretics or lithium.
When elevation is marked, it may be linked with symptoms such as:
- increased thirst and frequent urination
- constipation and reduced appetite
- tiredness or low energy
- confusion or difficulty concentrating
Mild elevations are often found incidentally on routine testing and cause no symptoms. Calcium is interpreted together with PTH, which helps distinguish a parathyroid cause from other explanations. These results describe a pattern, not a diagnosis, and should be discussed with a clinician.
What a low Calcium can mean
A low calcium level (hypocalcemia) can suggest that not enough calcium is being absorbed or held in the blood. Causes commonly associated with a low result include low vitamin D, underactive parathyroid glands (hypoparathyroidism), chronic kidney disease, and disturbances in magnesium, which the parathyroid glands need to work properly. A low albumin level can also lower total calcium while the active, unbound (free) portion stays normal, which is why an albumin-corrected value is often used.
When a true low is marked, it may be linked with symptoms such as:
- tingling in the fingers, toes, or around the mouth
- muscle cramps or twitching
- tiredness or irritability
Because a low total calcium can simply reflect low protein rather than a genuine deficiency, corrected calcium and the wider picture matter. Discuss any results with a clinician, who interprets them alongside PTH, vitamin D, and your symptoms.
Track your Calcium over time in Quanome — it reads your lab reports (PDF or photo) on your device, charts each marker against its range, and an AI coach explains what your trends mean alongside your Apple Health and DNA.