Calcium: what is it used for?


DECRYPTION – The dosage of this mineral essential to the skeleton is often integrated into the general blood test. It can highlight many problems.

What is it used for?

99% of the calcium provided by our diet ends up in our bones (and teeth), in the form of calcium phosphate. The rest circulates in the blood and is involved in nerve transmission, muscle contractions, coagulation, the transfer of information from one cell to another and various enzymatic reactions that generate energy.

The concentration of calcium in the blood is mainly regulated by parathormone and vitamin D. If the body lacks it (hypocalcaemia), the bones release it into the bloodstream in order to restore the balance. If the level of calcium in the blood is too high (hypercalcemia), the excess is stored in the bones or eliminated in the urine.

When is its dosage prescribed?

Calcium testing is usually part of a blood test. It can be prescribed in case of disorder at the origin of an excess or a deficiency in calcium. “Hyperparathyroidism (autoimmune abnormality), Kahler’s disease (bone cancer), excess vitamin D, sarcoidosis (inflammatory disease) or Paget’s disease of bone in children are accompanied by hypercalcemia, explains Dr. François Blanchecotte, national president of the Union of Biologists (SDB). The dosage of calcium also enters into the follow-up of cancer or the assessment of osteoporosis.

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How is it dosed?

The measurement of calcemia is done on an empty stomach, in general from a simple blood test in the crease of the elbow. Most often, the doctor prescribes a dosage of the total calcium circulating in the blood. In some cases, to obtain a more accurate reflection of serum calcium, he will ask for a “corrected calcium” (which also takes into account the albumin assay) or more rarely an “ionized calcium” (active form of calcium). If the doctor suspects osteoporosis, he may, in addition to the “total calcium”, request a calcium dosage in the urine collected over 24 hours.

How to interpret the results?

Normal value

Total serum calcium is between 2.18 and 2.60 millimoles per liter (mmol/l). This balance is essential to allow the bones to regenerate daily. In a healthy person, a diet sufficiently rich in dairy products (2 per day) generally provides a sufficient amount of calcium. Be careful, taking certain medications such as antacids containing calcium salts, lithium or vitamin D can interfere with the test results.

Low value

When the calcium level is below 2.18 mmol/l, it is called hypocalcemia. This can lead to osteoporosis. It is most often linked to a vitamin D deficiency, a kidney tumour, a lack of absorption from the intestine or a deficiency in parathyroid hormone (hypoparathyroidism) caused by an autoimmune disease, the removal of the parathyroid glands during a thyroidectomy (removal of the thyroid).

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High value

When the calcium level is higher than 2.60 mmol/l, it is called hypercalcemia. It can be the consequence of hyperparathyroidism (abnormally high production of parathyroid hormones), blood disease, bone metastases, and can lead to urinary stones.

To know

In the body, the level of calcium is determined by the diet, the absorption of calcium by the intestines and the activity of the parathyroid glands.

Calcium values ​​are very stable. When an anomaly appears in the dosage, it will often be interpreted by also taking into account the dosage of parathyroid hormone (PTH) and albumin (corrected calcium).

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