Ionised calcium – laboratory test

Description

Why ionised calcium is tested

Calcium in the blood exists in two main forms: bound to proteins, mainly albumin, and free, i.e. ionised. Ionised calcium makes up about half of total calcium and is its biologically active form: it is responsible for muscle contraction, heart function, the conduction of nerve impulses and blood clotting. Measuring total calcium is usually sufficient, because the body maintains a constant ratio between the two forms. However, when the protein concentration in the blood is abnormal or the total calcium result is outside the normal range, direct measurement of ionised calcium gives a better picture of the actual state of calcium balance. A value calculated from formulas using total calcium and albumin can be inaccurate.

When it is worth having this test

• when the total calcium result is abnormal and your doctor wants to verify it,
• when the concentration of protein or albumin in the blood is abnormal, e.g. in liver disease, malnutrition or nephrotic syndrome,
• in advanced chronic kidney disease,
• in the diagnosis and monitoring of parathyroid disorders,
• when you have symptoms that may be related to calcium disorders: muscle cramps and tingling, heart rhythm disturbances, weakness, kidney stones,
• after massive blood or plasma transfusions and in seriously ill patients, usually in a hospital setting.

How to prepare

• Come in the morning, rested after a night’s sleep, and rest for ten to fifteen minutes or so before the blood draw.
• Tell your doctor about all medicines and supplements you take, especially vitamin D and calcium preparations. Do not stop any medication on your own.
• The sample for this test is not very stable and requires quick, airtight preparation, which is why blood is collected only at collection points located at the laboratory.

How to read the result

The ionised calcium result depends on the pH of the blood and on how the sample is handled, which is why it is important to have the blood drawn at a point located at the laboratory. An abnormal result does not always mean a disease requiring treatment. The reference range printed on the laboratory report applies and depends on age.

What to test together

Total calcium, Parathyroid hormone (PTH), Vitamin D 25(OH), Magnesium, Phosphorus, Creatinine. More: Badania-Medyczne.pl.

Sources: ALAB laboratoria, Ionised calcium (preparation); Mayo Clinic Laboratories, Calcium, Ionized, Serum (uses, interpretation, sample requirements); MedlinePlus, Calcium Blood Test (total and ionised calcium, causes of abnormal results). For information only; it does not replace a medical consultation.