Calcium is one of the most common minerals in the body, and one of the most important. Calcium is important for cell signalling and to maintain muscle, nerve and heart function. Calcium is needed for coagulation of the blood and is crucial to the formation, density and maintenance of the skeleton.
Approximately 99% of all calcium is present in the skeleton, while the remaining 1% circulates in the blood. Calcium levels are strictly controlled, and if there is insufficient calcium in the blood or if the kidneys and intestines excrete too much calcium, calcium is taken from the skeleton in order to maintain the correct concentration of calcium in the blood.
A calcium test is carried out in order to screen, diagnose and monitor diseases related to the skeleton, heart, nerves, kidneys and teeth. It is also a good idea to do a calcium test if a person has symptoms indicating a parathyroid disease or an overactive thyroid.
If the results of a calcium test are outside the reference range, this is interpreted as a sign of an underlying problem. Helping to diagnose the underlying problem involves further tests in order to measure urinary calcium, phosphorus, magnesium, vitamin D, parathyroid hormones, etc. Parathyroid hormones and vitamin D are responsible for maintaining calcium concentrations within a narrow range in the blood.
If calcium levels are abnormal, it is possible to measure calcium and parathyroid hormones together to determine whether or not the parathyroid glands are functioning normally. Measuring urinary calcium can help to determine whether the kidneys are excreting the correct amount of calcium. Testing vitamin D, phosphorus and/or magnesium levels can help to determine whether any other deficiencies are present. Often the balance between these various substances (and changes to them) are just as important as the concentration of all substances.
Calcium can be used as a diagnostic test if a person has symptoms indicating:
The calcium test is usually ordered in order to evaluate calcium status. In most cases, it provides a good reflection of the amount of free calcium in the blood as the balance between free and bound calcium is normally stable and predictable. However, in some people the balance between bound and free calcium is disrupted. Under these circumstances, measurement of ionised calcium may be necessary. Some situations in which the ionised calcium test should be selected include: critically ill patients receiving blood transfusions or intravenous fluids, patients undergoing major surgery and people with blood protein abnormalities such as low albumin.
Major fluctuations in ionised calcium may cause the heart to slow down or beat too quickly, which may cause cramping in the muscles or even coma. In people who are seriously ill, it may be very important to monitor ionised calcium levels so that serious complications can be treated and prevented.
Many people have no symptoms of high or low calcium until their levels are a long way out of reach. These symptoms indicate that you should check your calcium levels:
Calcium monitoring may be very necessary in patients with certain types of cancer (particularly breast, lung, head and neck, kidney or multiple myeloma), or who have kidney disease or have had a kidney transplant. It may also be necessary to evaluate the efficacy of treatments, such as calcium or vitamin D supplements, if a patient has been treated for abnormal calcium levels.
Having high calcium levels is known as hypercalcaemia. Hyperparathyroidism and cancer are two of the most common causes of hypercalcaemia. Hyperparathyroidism involves an increase in parathyroid function, usually caused by a benign tumour in the parathyroid gland. This form of hypercalcaemia is normally mild and may occur for many years before it is noticed. Cancer may cause hypercalcaemia when it spreads to the bones and causes the release of calcium from the skeleton to the blood, or when cancer cells produce a hormone similar to the parathyroid hormone which results in increased calcium levels.
The causes of hypercalcaemia include:
Having low calcium levels is known as hypocalcaemia. Low blood protein levels, particularly low levels of albumin, are the most common cause of low total calcium. This may lead to liver disease or malnutrition, which may be the result of alcoholism or other diseases. Low albumin is also very common in people who are acutely ill.
The causes of hypocalcaemia include: