Kidneys, electrolytes and minerals
Calcium blood test: what a high or low result means
What a calcium blood test measures, what high or low calcium can mean, and what to ask your doctor.
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Explain my results → Available on web, iOS & Android.What is calcium?
Calcium is the main mineral in your bones and teeth, and the small amount in your blood is vital for your nerves, muscles and heart. Your body keeps blood calcium in a narrow range using parathyroid hormone and vitamin D. Because some calcium is carried by the protein albumin, many UK labs report an adjusted (or corrected) calcium that takes your albumin level into account.
Why is this test done?
- As part of a bone profile or routine blood test
- To investigate bone problems, kidney stones or tiredness
- To monitor kidney disease, vitamin D treatment or parathyroid conditions
- When someone has symptoms such as thirst, constipation, confusion or muscle cramps
What does a high calcium mean?
A high calcium is called hypercalcaemia (hypercalcemia in the US). Mildly high levels may cause no symptoms, while higher levels can cause thirst, constipation, tiredness or confusion.
Possible reasons include:
- An overactive parathyroid gland (primary hyperparathyroidism), a common cause
- Taking too much vitamin D or calcium
- Dehydration
- Some medicines, such as thiazide water tablets and lithium
- Some cancers
What does a low calcium mean?
A low calcium is called hypocalcaemia (hypocalcemia in the US). It can cause pins and needles, muscle cramps or spasms.
Possible reasons include:
- Low vitamin D
- Kidney disease
- Low magnesium
- Damage to the parathyroid glands, for example after neck surgery
- A low albumin level, which can make total calcium look low; adjusted calcium corrects for this
Why we don't list a "normal range". Reference ranges differ between laboratories and can depend on your age, sex and whether you are pregnant. The range printed next to your result on your own report is the one that applies to you, so use that, and talk to your doctor about what your result means for you.
What can affect your calcium result?
- Albumin level, which is why adjusted calcium is often reported
- Prolonged use of a tourniquet during the blood draw, which can cause fluid to shift and falsely raise total calcium
- Vitamin D and calcium supplements
- Dehydration
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Try it with your own results → Paste, upload or photograph your results.Questions to ask your doctor
- Is this my adjusted calcium, and is it high or low?
- Should my parathyroid hormone (PTH) or vitamin D be checked?
- Could my supplements or medicines be affecting it?
- Do I need a repeat test?
Frequently asked questions
What is adjusted or corrected calcium?
Nearly half of the calcium in blood is attached to proteins, mainly albumin. If your albumin is low or high, total calcium can be misleading, so labs adjust the result to estimate what it would be with a normal albumin.
Does high calcium mean I eat too much dairy?
Rarely. High blood calcium is usually caused by an overactive parathyroid gland, too much vitamin D, medicines or other conditions, not by diet alone.
Is blood calcium a test of bone strength?
No. Blood calcium is tightly controlled and usually normal even in people with weak bones. Bone strength is assessed with a bone density (DEXA) scan.
Can Patiently AI explain my calcium result?
Yes. Paste your results, or upload a photo, PDF or Word file, and Patiently AI explains them in plain English, sticking to the numbers and ranges on your own report rather than adding its own, and suggests questions to ask your doctor. It is free, needs no account, and removes identifying details on your device first.