Calcium
Serum Calcium
What this test measures
Calcium is essential for strong bones and teeth, muscle function, and nerve signals. Your body carefully controls calcium levels. This test checks if your calcium is in the normal range.
Understanding the numbers
Typical range: 2.2-2.6 mmol/L
Calcium results should be adjusted for albumin levels. Your GP will calculate the corrected calcium.
- Severe low: 1.5–1.9 mmol/L
- Low: 1.9–2.2 mmol/L
- Normal (corrected): 2.2–2.6 mmol/L
- Raised: 2.6–3.0 mmol/L
- Severe high: 3.0–3.5 mmol/L
Key numbers
- 2.2 mmol/L — Lower limit (corrected)
- 2.6 mmol/L — Upper limit (corrected)
- 3.0 mmol/L — Above = symptomatic hypercalcaemia likely
- 3.5 mmol/L — Critical — same-day hospital treatment
Calcium is always interpreted as 'corrected calcium' — adjusted for albumin. In primary care, the two commonest causes of raised calcium are primary hyperparathyroidism and malignancy. Low calcium often follows vitamin D deficiency, CKD, or surgery affecting the parathyroid glands.
Ranges can vary slightly between laboratories — your report may show slightly different numbers. This page does not read or interpret your result; your GP looks at it alongside your history and other tests.
What a higher-than-normal result can mean (Hypercalcaemia)
- Can cause tiredness, thirst, and confusion
- Often caused by overactive parathyroid glands
- Some cancers can raise calcium
- Too much vitamin D can also cause this
When not to wait
Very high or very low calcium can affect the heart, brain and muscles.
- Confusion, drowsiness, or fits
- Severe muscle cramps, spasms, or tingling around the mouth
- Palpitations or an irregular heartbeat
- Severe tummy pain or repeated vomiting
- Known calcium above 3.0 mmol/L or below 1.9 mmol/L
- Known cancer with new confusion or excessive thirst
Call NHS 111 for urgent advice, or 999 if someone is seriously unwell.
Questions you could ask your GP
- What might be causing my abnormal calcium?
- Do I need my parathyroid hormone (PTH) checked?
- Should I have my vitamin D level tested?
- Do I need a bone density scan?
Example stories
These are made-up examples to show how results are talked about in real appointments. They are not real patients.
Primary hyperparathyroidism
Leena's corrected calcium was 2.85, with raised PTH at 9.8 pmol/L and a vitamin D of 55. She had tiredness and a kidney stone last year.
What the GP said: “This is primary hyperparathyroidism — one of the parathyroid glands is overproducing PTH. The treatment is usually surgery to remove the abnormal gland; it fixes the calcium and the symptoms.”
What happened next: Leena had a parathyroidectomy. Her calcium normalised and her tiredness resolved over months.
Raised calcium with a raised or 'inappropriately normal' PTH is primary hyperparathyroidism. It's often missed because symptoms are vague — kidney stones, bone pain, tiredness, low mood. Surgery is curative in most cases.
Malignancy-related hypercalcaemia
Pieter had known myeloma. He became confused and dehydrated. Corrected calcium 3.2, PTH suppressed.
What the GP said: “Your calcium is dangerously high — this is hypercalcaemia of malignancy. I'm sending you to hospital for IV fluids and bisphosphonates today.”
What happened next: Admitted; IV fluids and zoledronate dropped calcium to 2.5 over 72 hours.
Very high calcium in someone with cancer is a palliative emergency. Aggressive fluids and IV bisphosphonates bring it down — untreated it can cause coma and arrhythmia.
Low calcium — vitamin D deficiency
Heera had muscle cramps and tingling around her mouth. Calcium 2.08, PTH raised at 12, vitamin D 18 (deficient).
What the GP said: “Your low calcium comes from severe vitamin D deficiency. I'll load you with high-dose vitamin D and a calcium supplement, and recheck in 8 weeks.”
What happened next: After vitamin D loading and maintenance, calcium was 2.3 and cramps resolved.
Vitamin D deficiency is the commonest cause of mild symptomatic hypocalcaemia. Replacing vitamin D first, with some calcium cover, usually resolves both the calcium and the symptoms.
Post-thyroidectomy hypocalcaemia
Two days after a total thyroidectomy, Carmen had tingling lips and painful hand cramps. Calcium 1.82, PTH very low.
What the GP said: “Your parathyroid glands have been affected by the surgery. You need IV calcium now, and we'll start calcium and calcitriol tablets. This may settle or need long-term treatment.”
What happened next: IV calcium settled symptoms. Maintenance calcium/calcitriol kept her in range; parathyroid function partially recovered over months.
Symptoms of low calcium (tingling, cramps, spasms) are an emergency, especially after thyroid surgery. Replacement is straightforward but sometimes long-term.
Before you act on anything here
This page is general information, written to help you understand — it is not personal medical advice and it cannot tell you what is right for you. Talk to your own GP, pharmacist or nurse about your own health.
- Need help now but it's not an emergency? Call NHS 111 or use 111.nhs.uk.
- Emergency? Call 999 or go to A&E.