Back Blood-tests Explained


Ionized Calcium


At a Glance

Why Get Tested?

To screen for, diagnose, and monitor a range of conditions

When to Get Tested?

As part of a routine metabolic panel; when you have symptoms of a disorder, or known presence of one, affecting your kidneys, bones, thyroid, parathyroid, or nerves or when symptoms of significantly increased or decreased calcium concentrations are present; when someone is critically ill, to monitor ionized calcium levels; when someone has certain types cancer; when someone is being treated for abnormal calcium levels, to evaluate the effectiveness of treatment

Sample Required?

A blood sample drawn from a vein in your arm; sometimes a random or a timed urine collection such as a 24-hour urine sample

Test Preparation Needed?

Current practices do not require fasting. You may be instructed to stop taking certain medications that can affect the test results, such as lithium, antacids, diuretics, and vitamin D supplements, among others.

The Test Sample

What is being tested?

Calcium is the most abundant and one of the most important minerals in the body. It is essential for cell signaling and the proper functioning of muscles, nerves, and the heart. Calcium is needed for blood clotting and is crucial for the formation, density, and maintenance of bones. This test measures the amount of calcium in the blood or urine.

About 99% of calcium is found complexed in the bones, while the remaining 1% circulates in the blood. Calcium levels are tightly controlled; if there is too little absorbed or ingested, or if there is excess loss through the kidney or gut, calcium is taken from bone to maintain blood concentrations.Roughly half of the calcium in the blood is "free" and is metabolically active. The remaining half is "bound" to albumin, with a smaller amount complexed to anions, such as phosphate, and these bound and complexed forms are metabolically inactive.

There are two tests to measure blood calcium. The total calcium test measures both the free and bound forms. The ionized calcium test measures only the free, metabolically active form.

Some calcium is lost from the body every day, filtered from the blood by the kidneys and excreted into the urine. Measurement of the amount of calcium in the urine is used to determine how much calcium the kidneys are eliminating.

How is the sample collected for testing?

A blood sample is taken by needle from a vein in the arm. If a urine collection is required, a 24-hour urine sample or a timed collection of a shorter duration is obtained. Sometimes a random urine collection may be used, although a timed collection is preferred.

Is any test preparation needed to ensure the quality of the sample?

Current practices do not require fasting. You may be instructed to stop taking certain medications, such as lithium, antacids, diurectics, and vitamin D supplements, among others, to ensure the most accurate test results.

The Test



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