Also Known As
Ca
Total calcium
Adjusted calcium
Ionised calcium
Formal Name
Calcium
This article was last reviewed on
This article waslast modified on 9 December 2024.
At a Glance
Why Get Tested?

For the diagnosis of a wide range of disorders including diseases of bone, kidney, parathyroid gland, or gastrointestinal tract and for monitoring the effectiveness of treatment for abnormal calcium. 

When To Get Tested?

Your doctor may request a calcium measurement in the following situations: 

  • If  you are found to have any symptoms and signs of abnormal calcium levels 
  • If you have kidney, bone, parathyroid, or nerve disease, 
  • If you are receiving treatment for abnormal calcium levels.  
Sample Required?

A blood sample taken from a vein in your arm;  
A spot urine collection may also be requested when blood calcium concentration is abnormal.  
A 24 hour urine calcium collection may be requested if you have kidney stones. 

Test Preparation Needed?

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. 

On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

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 only < 1% of calcium circulates in the blood.  

In the blood, total calcium is present in three forms: 

  • Free calcium, also refereed as non-protein bound calcium or ionised calcium (Ca2+) (physiologically active; about 50% of total plasma calcium)  
  • Protein‐bound (mainly to albumin; about 40–50% of total plasma calcium) 
  • Complexed (primarily with phosphate and citrate). 

There are two types of calcium tests measured in the laboratory 

  • Total calcium test, which measured both the free and protein bound calcium present in the circulation, 
    • Adjusted calcium (also known as corrected calcium) is commonly reported, which is calculated based on the measured total calcium concentration adjusted for the albumin concentration. This is because abnormally high or low albumin concentrations can alter total calcium concentration independently of the  free calcium concentration. Therefore, ‘adjusted calcium’ gives a better indication of the. physiologically active form of calcium 
  • Ionised calcium test, which measures the free calcium present in the circulation, 
    • Ionised calcium is only measured in some conditions, such as during major surgery (particularly after a blood transfusion), in critically ill patients, patients with abnormal protein concentration and patients with abnormal blood pH This is because the  ‘adjusted calcium’ concentration is likely to be misleading in these situations. is the test is performed  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. 

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Common Questions
  • 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, healthcare professionals 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. 

    Healthcare professionals 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?

    It is essential that calcium results are interpreted in relation to other analytes particularly urea, creatinine, phosphate, magnesium, alkaline phosphatase and PTH.  

    A normal blood adjusted calcium result with other normal laboratory results suggests no problems with calcium metabolism (use by the body). 

    A high adjusted calcium result is known as 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: 

    A low adjusted 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: 

    Urinary calcium concentrations may be affected by the same conditions and diseases as listed above. High amounts of calcium in the urine (known as hypercalciuria) may lead to the formation of crystals or stones in the kidney. 

    Is there anything else I should know?  

    Blood and urine calcium measurements cannot be used to assess how much calcium is in the bones. A test similar to an X-ray, called a bone density or 'Dexa' scan, is needed for this purpose. 

    How often should this test be performed? 

    This will be guided by the clinical situation and reason for request.

  • Is there anything else I should know?

    Blood and urine calcium measurements cannot be used to assess how much calcium is in the bones. A test similar to an X-ray, called a bone density or 'Dexa' scan, is needed for this purpose. 

  • 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?

    Dairy products are the main source of calcium, but lesser amounts are found in eggs, fish, green leafy vegetables, broccoli, beans and pulses, nuts, and whole grains. Many fruit juices now have calcium added. 

  • If I consume foods high in calcium, would it change my laboratory results?

    In general, consuming such foods will not affect your calcium test results. 

  • Can I perform this test at home?

    No. While there are hand-held instruments available, these are intended for use in a hospital or GP surgery setting and must be operated by trained personnel. 

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