Hypocalcaemia refers to low calcium levels in the blood. It is most commonly caused by either vitamin D deficiency or diseases of the parathyroid glands causing low parathyroid hormone (PTH) secretion.

Alternative names for hypocalcaemia

Calcium deficiency; hypocalcemia

What is hypocalcaemia?

Hypocalcaemia is a low level of calcium in the blood. In health, various hormones keep the blood calcium levels within a narrow range, but changes in the level of these hormones or, rarely, reduced consumption of calcium in the diet can lead to the calcium level dropping too low.

Calcium is found in many foods especially dairy products and milk, and most diets contain sufficient quantities of calcium. The major store of calcium in the body is within the bones, but it is found to some extent in most parts of the body. Vitamin D is required to absorb calcium from the gut into the bloodstream. Vitamin D is mostly produced in the skin in response to sunlight and is also absorbed from food eaten as part of a healthy balanced diet. The liver and kidneys convert vitamin D (produced in the skin and taken up in the diet), into the active form of vitamin D. Active vitamin D increases the amount of calcium that the gut can absorb from food in order to maintain healthy levels of calcium in the blood. The parathyroid glands sense the amount of calcium in the blood, and produce increased amounts of parathyroid hormone if the calcium level drops. This hormone helps to reduce the loss of calcium in the urine and releases some calcium from the bones. These two hormones work together to ensure that blood levels of calcium are maintained within the normal range.

What causes hypocalcaemia?

There are several possible causes of hypocalcaemia, including:

  • Low levels of vitamin D in the blood (vitamin D deficiency), which is common, particularly in people who only get limited exposure to the sun. Occasionally, diseases of the gut that affect absorptionof food can cause reduced vitamin D levels and diseases of either the liver or kidney can also contribute.
  • Reduced levels of parathyroid hormone(also known as hypoparathyroidism). This occurs as a result of surgical removal of the parathyroid glands or can be an inherited condition or rarely linked to autoimmunity against the parathyroid glands.
  • Not taking in enough calcium in the diet. In most cases, a diet that is poor in calcium can be compensated for by appropriate changes in the levels of vitamin D and parathyroid hormone in the blood. 
  • Rarer causes of hypocalcaemia, including some medications, severe infections and occasionally, bone diseases.

What are the signs and symptoms of hypocalcaemia?

The presence of symptoms, if any, depends on how low is the calcium in the blood and how quickly it dropped. Many people with hypocalcaemia will have no symptoms at all, especially if they have had the condition for some time. Most people who do have symptoms will note tingling around the mouth, and pins and needles or numbness in the hands. Muscle stiffness and cramps commonly occur, whilst confusion, difficulties in breathing, heart problems and locking of muscles in a fixed position (tetany), occur only when the calcium level is very low. 

How common is hypocalcaemia?

Mild hypocalcaemia is very common and is rarely associated with symptoms. Because of dietary effects on calcium and vitamin D levels, it particularly affects people with poor or restricted diets, people with lack of exposure to sunlight e.g. those who wear clothes that cover most of the skin or those who stay indoors a lot, such as elderly people in care homes. More severe hypocalcaemia is much rarer.

Is hypocalcaemia inherited?

Most cases of hypocalcaemia are not inherited, although some people with autoimmune parathyroid problems will have a family history of autoimmune problems affecting other endocrine glands (e.g. autoimmune polyglandular syndromes). 'Resistance to parathyroid hormone' (also known as pseudohypoparathyroidism) is a group of rare disorders where either the kidney, the bone or both do not recognise and respond to parathyroid hormone normally, and hypocalcaemia results. Depending on the features of the disorder, this can be passed on by either the mother or the father. 

How is hypocalcaemia diagnosed?

Calcium levels (along with vitamin D and parathyroid hormone levels) can be checked on a simple non-fasting blood sample, which can be carried out as an outpatient. Depending on the results, further tests may need to be carried out to establish the underlying cause of the hypocalcaemia.

How is hypocalcaemia treated?

Treatment of hypocalcaemia depends on the cause. Vitamin D can be given in tablet or injection form, if required, and this is often given with calcium supplements. If the cause of the hypocalcaemia is hypoparathyroidism, patients will also receive treatment for this condition in the form of active vitamin D or parathyroid hormone replacement. If a person has severe symptoms of hypocalcaemia, it may be necessary to give intravenous calcium in hospital to control severe symptoms.

Are there any side-effects to the treatment?

Most people do not have side-effects to treatment. Occasionally people taking calcium supplementation complain of a chalky taste in the mouth and constipation; higher doses (more than 1,500mg a day) can sometimes lead to stomach pain and diarrhoea. It is very rare for vitamin D treatment to cause raised levels of blood calcium above the normal range.

What are the longer-term implications of hypocalcaemia?

If a dietary or lifestyle explanation can be found for either low calcium or low vitamin D, it is sometimes possible to address this and patients make a full recovery. Persistent untreated hypocalcaemia has a tendency to cause build-ups of calcium and phosphate in parts of the body, including the brain, but this is rare. The doctor may also want to check for other associated conditions at regular intervals if the hypocalcaemia is the result of an autoimmune disease.

Last reviewed: Jul 2021