To determine the concentration of calcium in your blood
In persons with kidney, bone, parathyroid, or nerve disease, or if symptoms of abnormal calcium levels are present. To evaluate the effectiveness of being treated for abnormal calcium levels. Finally, to monitor levels in critically ill patients.
A blood sample taken from a vein in your arm; a urine collection may also be requested when blood calcium concentration is abnormal. Urine calcium measurements may also be requested if you have kidney stones.
Current practice does not require fasting or any other test preparation. However, it is advisable that prolonged tourniquet use and fist clenching during collection of the blood sample should be avoided as this may affect the generated result.
Calcium is one of the most important minerals in the body, required for proper functioning of muscles, nerves, heart, as well as essential in blood clotting and bone formation. About 99% of calcium is found in the bones, while most of the rest circulates in the blood. In the blood, roughly half of the calcium is ‘ionised’ (or free) and is active; the remaining half, is bound to proteins, such as albumin, or complexed with other compounds, such as phosphate and bicarbonate, and is inactive.
Most commonly, laboratories report a value for ‘adjusted calcium’, (also known as corrected calcium), which is the measured calcium value adjusted for the albumin concentration. This is because abnormally high or low albumin concentrations can alter total calcium concentration independently of ‘ionised’ (active) calcium concentration. Therefore, ‘adjusted calcium’ gives a better indication of the ‘ionised’ levels.
In some conditions, such as during major surgery (particularly after a blood transfusion), in critically ill patients, and patients with abnormal protein concentration, measurement of ‘ionised’ is needed, as ‘adjusted calcium’ level is likely to be misleading in these situations. In these situations, ‘ionised’ calcium is measured on specific analysers known as blood gas analysers or point of care (POC) analysers; thus special sample handling is required.
Urine calcium is used to indicate how much calcium is being excreted by the kidneys.
How is it used?
Calcium is tested to help diagnosis, and monitor a range of conditions relating to the bones, heart, nerves, and kidneys. The amount of calcium in the blood is controlled by the combined actions of parathyroid hormone (PTH) and 1, 25-dihydroxyvitamin D (Vitamin D).
Additionally, doctors can get a better understanding of the underlying problem by requesting additional tests such as phosphate, PTH, Vitamin D and magnesium. The balance among these and the changes in their concentration, help the doctor to assess the cause of any abnormality in calcium.
When is it requested?
For Diagnosis: Calcium can be used as a diagnostic test if individuals have symptoms that suggest::
- kidney stones
- bone disease, or
- neurologic (nerve-related) disorders.
Doctor may also request a calcium test if individuals have:
- kidney disease, because low calcium is common in those with kidney failure
- symptoms of excessive calcium, such as thirst, frequent or excessive urination, constipation, tiredness, weakness, loss of appetite or nausea and vomiting
- symptoms of low calcium, such as abdominal/muscle cramps, tingling fingers, numbness around the mouth, or convulsions
- other diseases that can be associated with abnormal blood calcium, such as thyroid disease, intestinal disease, cancer, or poor nutrition
However, if calcium levels fall slowly many people have no symptoms at all.
For Monitoring: Patients with certain kinds of cancer (particularly breast, lung, head and neck, kidney, and multiple myeloma), kidney disease or transplant may need calcium monitoring as part of their regular laboratory tests. Additionally, patients receiving calcium or vitamin D supplements may also need to have their calcium concentration monitored.
Urine calcium may be requested if individuals have symptoms of kidney stones, such as sharp pain in the side or back around the kidneys, pain that may progress to lower abdomen, and/or blood in the urine.
What does the test result mean?
A normal blood calcium result with other normal laboratory results suggests no problems with calcium metabolism (use by the body).
A high calcium level is called hypercalcaemia. Two of the main causes are:
- Hyperparathyroidism (increase in parathyroid gland function): this condition is usually caused by a benign (not cancerous) tumour on the parathyroid gland. This form of hypercalcaemia is usually mild and can be present for many years before being noticed.
- Cancer: Cancer can cause hypercalcaemia when it spreads to the bones, which releases calcium into the blood, or when cancer causes a hormone similar to PTH to increase calcium levels.
Other causes of hypercalcaemia include:
- Lithium treatment
- Prolonged immobilisation
- Acute kidney injury
- excess Vitamin D intake
High levels of 'free' calcium occur with all the above, except high protein levels.
A low calcium result is known as hypocalcaemia. The most common cause is a low protein concentration, especially of albumin, which can result from liver disease or malnutrition.
Some other causes of hypocalcaemia include:
- Decreased vitamin D concentration
- Decreased dietary intake of calcium
- Underactive parathyroid gland (hypoparathyroidism)
- Magnesium deficiency
- Acute inflammation of the pancreas (pancreatitis)
- Chronic kidney disease
- Bone disease, such as Osteomalacia (adults) and rickets (children)
Urinary calcium concentrations may be affected by the same conditions and diseases as listed above. High amounts of calcium in the urine (hypercalciuria) may lead to the formation of crystals or stones in the kidney.
Is there anything else I should know?
Should I take a calcium supplement?
A healthy diet should contain enough calcium, however some individuals do not take enough calcium in their diet and may need to consider supplementation Calcium is particularly important in growing children, to maintain bone growth, and in post-menopausal women who may develop low bone mass and be at risk of osteoporosis. It is important to discuss with your doctor the risks and benefits of starting a supplement.
What foods are high in calcium?
If I consume foods high in calcium, would it change my laboratory results?
Can I perform this test at home?
On This Site
Tests: Phosphate, Vitamin D, Parathyroid Hormone (PTH), Albumin; Magnesium; Kidney Stone Analysis; Kidney Stone Risk Panel
Conditions: Kidney disease; Thyroid disease; Breast Cancer; Multiple Myeloma; Alcoholism