High Calcium (Hypercalcaemia)
Calcium keeps bones strong and nerves, muscles and the heart working. Its level is tightly controlled by parathyroid hormone (PTH) and vitamin D. When it’s high, PTH is the test that points to the cause.
Quick answer: Adjusted calcium above 2.60 mmol/L (10.4 mg/dL) is high. About 9 in 10 cases are due to an overactive parathyroid gland or cancer, so PTH is the key next test. Under 3.0 is mild and often symptom-free. Over 3.5 mmol/L (14 mg/dL) is an emergency.
What the test measures
About half the calcium in blood is attached to albumin, a protein. Because albumin levels vary, labs often report an adjusted or corrected calcium. Some also measure ionised (free) calcium directly. Calcium is controlled by parathyroid hormone from four tiny glands in the neck, by vitamin D, and by the kidneys.
Typical adult ranges
- Total or adjusted calcium: 2.10–2.60 mmol/L (8.4–10.4 mg/dL)
- Mildly high: up to 3.0 mmol/L (12 mg/dL)
- Moderately high: 3.0–3.5 mmol/L
- Severely high: over 3.5 mmol/L (14 mg/dL)
What a high result usually means
Common causes:
- Primary hyperparathyroidism: usually one small, benign parathyroid gland growth making too much PTH. The commonest cause in people who feel well, often found by chance, and more common in women after menopause.
- Cancer: the commonest cause in people who are unwell in hospital, from bone spread or a PTH-like hormone. Together, these two cause about 90% of cases.
- Medicines: thiazide diuretics (such as hydrochlorothiazide and indapamide), lithium, and too much vitamin D or calcium with vitamin D.
- Dehydration, and a tourniquet left on too long when blood is taken (a false high).
Less common but important:
- Familial hypocalciuric hypercalcaemia (FHH): an inherited, harmless rise, picked up with a urine calcium test. It doesn’t need surgery.
- Myeloma, sarcoidosis and tuberculosis.
- Overactive thyroid, long periods in bed, Paget’s disease of bone, and adrenal insufficiency.
How PTH helps: high calcium with a high or high-normal PTH points to hyperparathyroidism (or FHH). High calcium with a low PTH points away from the parathyroids, towards cancer, vitamin D excess, sarcoidosis and other causes.
Symptoms
- Often none when mild.
- Thirst and passing a lot of urine, constipation, nausea and tummy pain.
- Kidney stones, bone pain and fractures.
- Tiredness, low mood, poor concentration, muscle weakness, and confusion when severe.
What happens next
- Repeat adjusted calcium with PTH at the same time. NICE advises measuring PTH when adjusted calcium is 2.6 mmol/L or more on two occasions, or 2.5 or more twice if hyperparathyroidism is suspected.
- Kidney function, phosphate and vitamin D, and a medicine review.
- Urine calcium to rule out FHH.
- Hyperparathyroidism: referral to a parathyroid surgeon is advised for symptoms, kidney stones, fragility fractures or osteoporosis, or an adjusted calcium of 2.85 mmol/L or more. Surgery cures most people.
- Low PTH: tests for cancer, myeloma, vitamin D excess and sarcoidosis, often with a specialist.
- Drink enough fluids, and don’t take extra calcium or vitamin D supplements until you’ve spoken to your doctor.
Get urgent help (go to an emergency department or call 000 in Australia, or your local emergency number) if your adjusted calcium is over 3.5 mmol/L (14 mg/dL), or at any level with confusion, drowsiness, severe vomiting, severe thirst with dehydration or palpitations: very high calcium can affect the heart rhythm. See a doctor the same day for a calcium of 3.0–3.5 mmol/L, especially with symptoms.
Practise reading results. Play Panelysis, the daily blood-test puzzle: a fictional patient, a real-looking panel, three guesses. More in medical games.
Common questions
Is a calcium of 2.7 dangerous?
It’s mildly high and not an emergency if you feel well. The next step is a repeat adjusted calcium with a PTH level, kidney function and vitamin D, and a check of your medicines. The commonest cause at this level is an overactive parathyroid gland.
What is the most common cause of high calcium?
In people who feel well, primary hyperparathyroidism, usually a single benign parathyroid gland growth. In people unwell in hospital, cancer is more common. Together they cause about 90% of high calcium results.
Can calcium tablets cause high calcium?
Not usually on their own at normal doses. Large doses, especially combined with high-dose vitamin D, or in people with kidney problems, can raise calcium. Bring a list of your supplements to your GP.
Is high calcium a sign of cancer?
Sometimes, but in people who feel well an overactive parathyroid gland is far more common. Cancer is more likely when calcium is very high, rising quickly, PTH is low, or there are symptoms such as weight loss or bone pain.
What is corrected or adjusted calcium?
About half of blood calcium is bound to albumin. Corrected (adjusted) calcium is a calculation that allows for your albumin level, so the result reflects the active calcium more accurately.
Does hyperparathyroidism need surgery?
Not always. Surgery is advised for symptoms, kidney stones, osteoporosis or fractures, or a calcium of 2.85 mmol/L or more. Removing the overactive gland cures most people. Others are monitored.
Evidence and more information
- Pathology Tests Explained (RCPA): Calcium (adult range and causes)
- Pathology Tests Explained (RCPA): Parathyroid hormone (PTH)
- Society for Endocrinology: Emergency guidance, acute hypercalcaemia in adults (severity bands)
- NICE NG132: Hyperparathyroidism (primary), diagnosis, assessment and initial management
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