Description
Overview:
Total calcium in the blood exists in two main forms: about half is attached to proteins (primarily albumin), and the other half is “free” or ionized. Ionized calcium is the physiologically active form that the body actually utilizes. This test specifically measures only that active, free fraction.
Why is this test different from “Total Calcium”?
A standard “Total Calcium” test measures both bound and unbound calcium. If a patient has low protein levels (common in liver disease, malnutrition, or nephrotic syndrome), their “Total Calcium” might appear low even though their active “Ionized Calcium” is normal. Conversely, high protein levels can falsely elevate total calcium. The Ionized Calcium test bypasses these protein interference issues to show the true functional calcium status
When is this test recommended?
This test is often ordered in more complex clinical situations where a standard Total Calcium test might be misleading:
Critically Ill Patients: Patients in ICUs, those with sepsis, or multi-organ failure.
Major Surgery/Blood Transfusions: Large blood transfusions contain citrate, which binds to ionized calcium and can cause a rapid, dangerous drop in active calcium levels.
Abnormal Protein Levels: Patients with liver disease or kidney disease where albumin levels fluctuate.
Parathyroid Disease: For precise monitoring of hyper- or hypoparathyroidism.
Sample Requirements:
Specimen: Serum.
Container: Gold Top (SST) or Red Top Tube.
Special Handling (Crucial): Ionized calcium is extremely sensitive to pH changes caused by exposure to air. Samples should ideally be collected anaerobically (tube kept vacuum-sealed) and processed rapidly by the lab to ensure accuracy.
