Calcium
Calcium is the mineral that keeps your bones, muscles and nerves working and helps your blood clot. Most is stored in your bones; this test checks the small amount travelling in your blood. A result inside your report's range is the usual, reassuring picture. If it sits high or low, that is a prompt for your GP to look closer, not a cause for alarm.
Standard CareWhat is calcium?
Calcium is a mineral used by every cell in your body. As the RCPA describes, it "is used by every cell in your body and helps with nerve signalling, muscle contractions and keeping your heart pumping. It is also needed for blood clotting." Healthdirect adds: "calcium is a mineral that helps build strong bones and teeth. Most calcium in your body is stored in your bones." Blood calcium exists in two forms. One circulates freely and is called free or ionised calcium — this is the active form your cells use. The other is bound mostly to the protein albumin (a protein made by the liver) in your blood. The total calcium test measures both forms together. Because a low albumin level causes the total calcium to read falsely low, your laboratory may also report a corrected (or albumin-adjusted) calcium: a version that "takes the total calcium and adjusts it for changes in a protein called albumin, giving a slightly more accurate total calcium score." Calcium levels are regulated by two main controls: parathyroid hormone (PTH), produced by four small glands in the neck, and vitamin D, which helps the gut absorb calcium from food.
Why is it tested?
A blood calcium test is often ordered as part of routine screening or when investigating symptoms such as muscle cramps, tingling, bone pain, or persistent fatigue. It is also ordered when checking the effect of conditions that affect bone or mineral metabolism, or when a parathyroid or vitamin D problem is suspected. Because calcium, PTH, and vitamin D work as a system, your GP usually orders at least two of the three together to understand the full picture.
Reference range (Australia)
The AHRIA harmonised reference interval (AACB/RCPA-endorsed) applies to both total calcium and albumin-adjusted (corrected) calcium for adults of all sexes. Corrected calcium adjusts the total for your albumin level; use the range printed on your own report when reading your result.
Reference intervals vary between laboratories. Always use the range printed on your own report.
What your result means
A calcium below the reference range is called hypocalcaemia — too little calcium in the blood. Healthdirect identifies the most common reasons: "may happen due to low vitamin D levels, kidney problems or not enough albumin (a protein) in your blood." Low albumin in particular can give a falsely low total calcium reading, which is why the corrected (albumin-adjusted) calcium matters. To make sense of a low result, your GP will look at vitamin D and PTH next to the calcium, and may ask about your diet and any medicines you take.
A calcium within the reference range suggests your body's calcium-regulating system — parathyroid hormone, vitamin D, and the kidneys — is working as expected. A normal corrected calcium alongside a normal PTH is especially reassuring. Keeping vitamin D at an adequate level and eating a varied diet supports bone and mineral health over the long term.
A calcium above the reference range is called hypercalcaemia — too much calcium in the blood. The most common cause by some distance is an overactive parathyroid gland (one of four tiny glands in your neck that control your blood calcium; doctors call this primary hyperparathyroidism). The gland makes too much parathyroid hormone (PTH) and releases more calcium from bone than is needed. Too much vitamin D, and some other conditions, can also raise calcium. A persistently high calcium is worth looking into; as healthdirect notes, causes range from common ones like an overactive parathyroid gland, to excess vitamin D, to — less often — other illnesses such as cancer. To work out which is most likely, your GP will usually check PTH and vitamin D at the same time as the calcium.
What can affect your result
The two main regulators of blood calcium are parathyroid hormone (PTH) and vitamin D. When blood calcium falls, the parathyroid glands release more PTH to release calcium from bone, keep more calcium in the bloodstream via the kidneys, and activate vitamin D to improve gut absorption. When calcium rises, the glands reduce PTH output. Albumin levels strongly affect the total calcium reading. A low albumin — which can occur with liver disease, poor nutrition, or some chronic illnesses — will make total calcium appear falsely low, which is why corrected calcium is often reported alongside it. Some medicines can shift calcium: calcium supplements and high-dose vitamin D supplements can raise it, while medicines that affect kidney function can interfere with how the kidneys regulate calcium. Dehydration can also concentrate calcium temporarily.
When to act
If your calcium is outside the reference range, your GP may look at PTH and vitamin D alongside it, because calcium is hard to interpret on its own. A mildly abnormal result by itself is not a diagnosis. Symptoms such as persistent muscle cramps, tingling in the hands or feet, or bone pain alongside an abnormal calcium are worth mentioning when you see your GP — they add important context. A calcium that is persistently outside the range warrants follow-up to find the cause, but most causes are manageable once identified. This page is general information and is not a substitute for advice from your GP.
Frequently asked questions
Test your calcium
NATA-accredited testing. Results in 2–5 days. No GP referral required.
View Calcium