Ionized calcium measures the free, unbound fraction that is physiologically active in nerve conduction, muscle contraction and clotting. It is regulated moment to moment by parathyroid hormone and vitamin D. Unlike the total, it is independent of albumin, so it represents calcium status directly.
No readings for this marker yet.
Raised ionized calcium most often reflects overactive parathyroid tissue or excess vitamin D and calcium supplementation. Lowered values most often accompany vitamin D deficiency, chronic kidney disease, low parathyroid function, or acute illness such as pancreatitis or sepsis. The test is usually ordered when total calcium is ambiguous, and it is the more reliable of the two in that situation. Interpretation belongs with a doctor.
The measurement is sensitive to blood pH: alkalosis, including hyperventilation before or during the draw, shifts calcium onto albumin and lowers the free fraction, while acidosis raises it. Samples must be handled anaerobically and processed promptly, and a prolonged tourniquet distorts the result. It is read together with total calcium, albumin, magnesium, phosphorus, vitamin D and parathyroid hormone.
Reference ranges are general adult values and depend on lab, assay, age and sex. For orientation, not diagnosis — discuss results with your doctor.