Calcium, Total, Serum
Diagnosis and monitoring of a wide range of disorders including disorders of protein and vitamin D, and diseases of bone, kidney, parathyroid gland, or gastrointestinal tract
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
The calcium content of an adult is somewhat over 1 kg (about 2% of the body weight). Of this, 99% is present as calcium hydroxyapatite in bones and less <1% is present in the extra-osseous intracellular space or extracellular space (ECS). The calcium level in the ECS is in dynamic equilibrium with the rapidly exchangeable fraction of bone calcium. In serum, calcium is bound to a considerable extent to proteins (approximately 40%), 10% is in the form of inorganic complexes, and 50% is present as free or ionized calcium.
Calcium ions affect the contractility of the heart and the skeletal musculature, and are essential for the function of the nervous system. In addition, calcium ions play an important role in blood clotting and bone mineralization.
Hypocalcemia is due to the absence or impaired function of the parathyroid glands or impaired vitamin-D synthesis. Chronic renal failure is also frequently associated with hypocalcemia due to decreased vitamin-D synthesis as well as hyperphosphatemia and skeletal resistance to the action of parathyroid hormone (PTH). A characteristic symptom of hypocalcemia is latent or manifest tetany and osteeomalacia.
Hypercalcemia is brought about by increased mobilization of calcium from the skeletal system or increased intestinal absorption. The majority of cases are due to primary hyperparathyroidism (pHPT) or bone metastasis of carcinoma of the breast, prostate, thyroid gland, or lung. Patients who have pHPT and bone disease, renal stones or nephrocalcinosis, or other signs or symptoms are candidates for surgical removal of the parathyroid gland(s). Severe hypercalcemia may result in cardiac arrhythmia.
Total calcium levels also may reflect protein levels.
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.
0-11 months: not established
1-14 years: 9.6-10.6 mg/dL
15-16 years: 9.5-10.5 mg/dL
17-18 years: 9.5-10.4 mg/dL
19-21 years: 9.3-10.3 mg/dL
> or =22 years: 8.9-10.1 mg/dL
0-11 months: not established
1-11 years: 9.6-10.6 mg/dL
12-14 years: 9.5-10.4 mg/dL
15-18 years: 9.1-10.3 mg/dL
> or =19 years: 8.9-10.1 mg/dL
Long-term therapy must be tailored to the specific disease causing the hypocalcemia. The therapeutic endpoint is to achieve a serum calcium level of 8.0 to 8.5 mg/dL to prevent tetany. For symptomatic hypocalcemia, calcium may be administered intravenously.
The level at which hypercalcemic symptoms occur varies from patient to patient. Symptoms are common when serum calcium levels are >11.5 mg/dL, although patients may be asymptomatic at this level. Levels >12.0 mg/dL are considered a critical value in the Mayo Health System. Severe hypercalcemia (>15.0 mg/dL) is a medical emergency.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Gadolinium is known to interfere with most metals tests. If gadolinium-containing contrast media has been administered a specimen can not be collected for 48 hours.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Tietz Textbook of Clinical Chemistry, Edited by CA Burtis, CR Ashwood. WB Saunders Company, Philadelphia, 1999
2. Baldwin TE, Chernow B: Hypocalcemia in the ICU. J Crit Illness 1987;2:9-16