Calcium (Ca)

What is calcium?

Calcium is the most abundant mineral in the body, and almost all of it is stored in the bones and teeth. The small remaining portion is found in the blood and cells; it is needed for muscle contraction, nerve conduction, regulation of the heart rhythm and blood clotting. Milk and dairy products, green leafy vegetables, nuts and fish eaten with their bones are the main dietary sources.

The blood calcium level is kept within a narrow range by hormones such as parathyroid hormone, vitamin D and calcitonin. Part of this calcium is bound to proteins such as albumin, while about half circulates in free, or ionized, form; free calcium is the form the body actually uses. This test measures total calcium, and the result is reported in mg/dL; if the albumin level is low, the result may be corrected for interpretation.

When is a calcium test ordered?

Calcium is frequently included in routine biochemistry panels and provides the first clue in many situations. When a result is abnormal, the doctor usually orders additional tests such as parathyroid hormone, vitamin D, phosphorus and albumin.

In conditions that can disturb calcium balance, such as kidney disease, parathyroid gland diseases and certain types of cancer, the test is repeated at regular intervals. People who have been bedridden for a long time may need checks, as calcium release from the bones can increase. It may also be ordered for monitoring in people being treated with medications that can affect calcium levels.

• Muscle cramps, numbness in the fingertips or around the mouth
• Excessive thirst, constipation, nausea or weakness
• Kidney stones or kidney disease
• Suspected parathyroid gland disease or osteoporosis
• Monitoring people who take calcium or vitamin D supplements

How do you prepare for a calcium test?

In most cases, no fasting is needed for the calcium test; however, if it has been ordered together with other tests that require fasting, your doctor may ask you to be fasting in the morning. Because leaving the tourniquet on for a long time or repeatedly clenching and opening the fist while blood is drawn can raise the result, the procedure is completed quickly. It is fine to continue your usual eating and fluid intake before the test.

Calcium and vitamin D supplements, certain diuretics, lithium and medications that neutralize stomach acid can affect calcium levels. Tell your doctor which supplements you take and at what doses, and do not change your prescribed medications without their knowledge. If you take supplements, it is also helpful to note when you took the last dose. Our nurse can take your blood sample from a vein in your arm at your home or workplace.

What does a calcium result mean?

The most common causes of high calcium are an overactive parathyroid gland and certain types of cancer. Excess vitamin D, prolonged immobility, certain diuretics and medications such as lithium can also raise the value. Mild elevations often cause no symptoms and are discovered incidentally during routine checks; a marked elevation, however, can lead to nausea, constipation, excessive thirst, frequent urination and weakness.

Low total calcium, by contrast, is often due to low albumin and may not reflect a true deficiency. A truly low calcium level may be linked to conditions such as vitamin D deficiency, insufficient parathyroid hormone, kidney disease, magnesium deficiency or pancreatitis, and can cause muscle cramps and numbness. The reference range may differ from laboratory to laboratory and by age and sex; you can find the range of the laboratory that analyzes your sample on this page. It is up to your doctor to assess your calcium result together with your symptoms and other tests, such as albumin.