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Calcium And Phosphates - Deficiency Test

The calcium and phosphates test measures the urine levels of calcium and phosphates, elements essential for the formation and resorption of bone. Urine calcium and phosphate levels generally parallel serum levels.

Normally absorbed in the upper intestine and excreted in stool and urine, calcium and phosphates help maintain tissue and fluid pH, electrolyte balance in cells and extracellular fluids, and permeability of cell membranes. Calcium promotes enzymatic processes, aids blood coagulation, and lowers neuromuscular irritability; phosphates aid carbohydrate metabolism.

Purpose

• To evaluate calcium and phosphate metabolism and excretion
• To monitor treatment of calcium or phosphate deficiency

Patient preparation

• Explain to the patient that this test measures the amount of calcium and phosphates in the urine.
• Encourage him to be as active as possible before the test.
• Tell him the test requires urine collection over a 24-hour period.
• If the patient is to collect the specimen, teach him the proper technique.
• Provide the Albright-Reifenstein diet (which contains about 130 mg of calcium/24 hours) for 3 days before the test or provide a copy of the diet for the patient to follow at home.

Procedure and posttest care

• Collect the patient's urine over a 24 hour period.
• Observe a patient with low urine calcium levels for tetany.

Precautions

• Tell the patient not to contaminate the specimen with toilet tissue or stool.

Reference values

Normal values depend on dietary intake. For a normal diet, urine calcium levels for a 24-hour period range from 25 to 300 mg/24 hours in males and 20 to 275 mg/24 hours in females. Normal excretion of phosphate is less than 1,000 mg/24 hours.

Abnormal findings

A variety of disorders may affect calcium and phosphorus levels. (See Disorders that affect urine calcium and urine phosphorus levels.)

Interfering factors

• Contamination of the specimen with toilet tissue or stool.
• Thiazide diuretics, sodium phosphate, and glucocorticoids.