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Test ID: CAS    
Calcium, Total, Serum

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

The diagnosis and monitoring of a wide range of disorders including diseases of bone, kidney, parathyroid gland, or gastrointestinal tract   Calcium levels may also reflect abnormal vitamin D or protein levels

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 <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 osteomalacia.

 

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.

Males

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

Reference values have not been established for patients who are <12 months of age.

Females

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

Reference values have not been established for patients who are <12 months of age.

Interpretation Provides information to assist in interpretation of the test results

Hypocalcemia:

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.

 

Hypercalcemia:

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

The interference of intravenously administered gadolinium containing MRI (magnetic resonance imaging) contrast media was tested (Omniscan,Optimark) but no interference was found at the therapeutic concentration. Interferences at higher concentrations were observed.

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, 1994

2. Baldwin TE, Chernow B: Hypocalcemia in the ICU. J Crit Illness 1987;2:9-16