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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
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.
IONIZED CALCIUM
< 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
pH
< 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
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.
Proper specimen handling is necessary to ensure accurate results.
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