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Biochemistry
Calcium in your blood does far more than build bone — it's needed for your heart to beat in rhythm, your muscles to contract, your nerves to send signals, and your blood to clot when you're cut. About half the calcium circulating in your blood travels freely, and the other half is bound to albumin, a blood protein, which matters because a low albumin level can make your total calcium reading look lower than the amount your body actually has available. A result outside the normal range rarely stands alone as an answer — it usually opens a search across your bones, kidneys, thyroid, or parathyroid glands, since all of them help keep blood calcium steady.
The test reports total calcium in your blood, in milligrams per decilitre. Because roughly half of that total is bound to albumin, your doctor may check albumin alongside it, or ask for a separate ionised calcium test that measures only the free, unbound portion. A result above the normal range (hypercalcaemia) or below it (hypocalcaemia) doesn't say why on its own — that depends on which other systems, such as the parathyroid glands or kidneys, are also out of balance.
A typical adult normal range runs from about 8.8 to 10.3 mg/dL, though individual labs may set slightly different cutoffs. High calcium most often traces back to overactive parathyroid glands, which control calcium levels directly, but it can also come from certain cancers, prolonged bed rest, or taking in too much calcium or vitamin D. Low calcium has a different, mostly separate set of causes — underactive parathyroid glands, kidney disease, vitamin D deficiency, low magnesium, or conditions that stop your gut from absorbing nutrients properly.
Because several medicines can shift calcium readings, your doctor may ask you to pause certain ones beforehand — calcium supplements, lithium, thiazide diuretics, levothyroxine, and vitamin D are commonly mentioned examples — though whether that applies to you, and for how long, is something to confirm directly rather than assume.
A single abnormal calcium result is often followed up rather than acted on immediately, particularly when it's only mildly outside range, since albumin levels, hydration, and even how the sample was drawn can all nudge the number. Repeating the test, sometimes alongside albumin or parathyroid hormone, is the usual next step before deciding what an abnormal calcium level actually means for you.
Roughly 8.8 to 10.3 mg/dL for most adults, though the exact range printed on your report may differ slightly by lab.
About half the calcium in your blood is bound to albumin. If your albumin is low, your total calcium reading can look lower than the calcium that's actually freely available to your body, which is why the two are sometimes checked together.
Overactive parathyroid glands are the most common cause. Certain cancers, prolonged bed rest, and too much calcium or vitamin D intake can also raise it.
Underactive parathyroid glands, kidney disease, vitamin D deficiency, and low magnesium are common causes, along with conditions that interfere with nutrient absorption in the gut.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
Possibly — calcium supplements, lithium, thiazide diuretics, levothyroxine, and vitamin D are known to affect results. Ask your doctor or the centre whether this applies to you before the test.
No. Total calcium includes both the albumin-bound and free portions. Ionised calcium measures only the free, biologically active portion directly, and is sometimes ordered separately when albumin levels are abnormal.
Not necessarily. Mildly abnormal results are often repeated, sometimes alongside albumin or parathyroid hormone, before your doctor draws conclusions.