Test Catalog

Test ID: CAI    
Calcium, Ionized, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Assessing calcium states during liver transplantation surgery, cardiopulmonary bypass, or any procedure requiring rapid transfusion of whole blood in neonates and critically ill patients


Second-order test in the evaluation of patients with abnormal calcium values

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Ionized calcium, which accounts for 50% to 55% of total calcium, is the physiologically active form of calcium.


Low ionized calcium values are often seen in renal disease, critically ill patients, or patients receiving rapid transfusion of citrated whole blood or blood products.


Increased serum ionized calcium concentrations may be seen with primary hyperparathyroidism, ectopic parathyroid hormone-producing tumors, excess intake of vitamin D, or various malignancies.


Nomograms have been used to calculate ionized calcium from total calcium, albumin, and pH values. However, calculated ionized calcium results have proven to be unsatisfactory. A Mayo study of 114 patients found significant differences between ionized and total calcium in 26% of patients.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.


< or =13 days old: not established

14 days-<1 year: 5.21-5.99 mg/dL

1-<2 years: 5.04-5.84 mg/dL

2-<3 years: 4.87-5.67 mg/dL

3-<24 years: 4.83-5.52 mg/dL

24-< or =97 years: 4.57-5.43 mg/dL

> or =98 years: not established



< or =13 days old: not established

14 days-97 years old: 7.35-7.48

> or =98 years old: not established


For SI unit Reference Values, see International System of Units (SI) Conversion

Interpretation Provides information to assist in interpretation of the test results

Serum ionized calcium concentrations 50% below normal will result in severely reduced cardiac stroke work. With moderate to severe hypocalcemia, left ventricular function may be profoundly depressed.


Ionized calcium values are higher in children and young adults.


Ionized calcium result has been adjusted to pH 7.40 to account for changes in specimen pH that may occur during transport. Ionized calcium concentration increases approximately 0.2 mg/dL per 0.1 pH unit decrease.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Proper specimen handling is necessary to ensure accurate results.

Clinical Reference Recommendations for in-depth reading of a clinical nature

Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Edited by Carl A Burtis, Edward R Ashwood, David E Bruns. St. Louis, MO, Elsevier Saunders, 2012