Blood
Ionized Calcium (Ca²⁺)
CONVERT & COMPARE
mg/dL
=
1.25
mmol/L
=
2.5
mEq/L
Reference ranges by source
Published adult intervals: 4, from 3 named sources, shown in mg/dL.
SOURCE
SEX
AGE
RANGE
VISUAL
CITE
Ages 0–17 (CALIPER)
3 age- and sex-stratified entries from the Canadian Laboratory Initiative on Pediatric Reference Intervals.
SOURCE
SEX
AGE
RANGE
VISUAL
CITE
About Ionized Calcium (Ca²⁺)
A calcium blood test measures the amount of calcium in your blood. Too much or too little calcium in your blood may be a sign of a wide range of medical conditions, such as bone disease, thyroid disease, parathyroid disorders, kidney disease, and other conditions.
Calcium is one of the most important minerals in your body. About 1% of the calcium in your body is in your blood. The rest is stored in your bones and teeth. Having the right amount of calcium in your blood is necessary for your nerves, muscles, and heart to work properly. It also helps blood vessels move blood throughout your body and helps release hormones that affect many body functions. Calcium also plays a role in muscle and nerve signaling, enzyme activity, bone metabolism, and blood clotting, and its level in the blood is regulated by parathyroid hormone, vitamin D, calcitonin, and adrenal steroid hormones.
An ionized calcium test measures only the "free calcium" in your blood that isn't attached to proteins. This is the form of calcium your body can actually use, sometimes called the bioavailable calcium. Because most calcium in the bloodstream is bound to proteins (especially albumin), changes in protein levels can make total calcium results misleading. Measuring ionized calcium can give a more accurate picture when total calcium results don't match the clinical picture, such as in conditions like hyperparathyroidism.
An ionized calcium test is more difficult to do, so it's usually ordered if the results of a total calcium test aren't normal. You may also have this test if you have a condition that affects your body's ability to balance the amounts of ionized and bound calcium in your blood or if you are seriously ill or having surgery.
Main source: MedlinePlus ↗
Useful for
Checking your general health as part of a routine blood panel
Helping diagnose or monitor conditions that affect your bones, kidneys, digestive system, thyroid, or parathyroid glands
Measuring only the active, usable form of calcium in your blood when total calcium results don't match your symptoms
Evaluating calcium balance when your protein levels are abnormal or you are seriously ill or having surgery
Helping investigate possible parathyroid disorders that affect how your body controls calcium
Main source: MedlinePlus ↗
Interpretation
Because ionized calcium reflects the active form of calcium in your blood, it can sometimes be high even when total calcium looks normal, especially if your protein levels are abnormal. Your provider will look at your ionized calcium together with other tests to understand what's going on.
If your results from a calcium blood test are not in the normal range, it doesn't always mean that you have a medical condition that needs treatment. Your diet and certain medicines can affect your calcium levels. If you have questions about your results, talk with your provider.
For general wellness information only. Talk to a clinician about your specific results.
Main source: MedlinePlus ↗
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Related biomarkers
More tests in the blood category.
Sources
Last updated 2026-05-02
This page presents source-specific reference data and sourced explanations. For general wellness information only. This is not medical advice. For diagnosis or treatment of any condition, talk to a qualified clinician.