Phosphorus, 24-Hour Urine

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Turnaround Time: 1 - 2 days
CPT Code:


Test Type: 10 mL aliquot of entire collection, Urine
Stability Time:



Room temperature

14 days


14 days


14 days

Freeze/thaw cycles

Stable x3

Reference Range:


Male (mg/24 hr)

Female (mg/24 hr)

0 to 5 y

Not established

Not established

6 to 12 y



13 to 80 y



>80 y




Evaluate calcium/phosphorus balance.

High urinary phosphorus (ie, increased renal losses) occurs in primary hyperparathyroidism, vitamin D deficiency, renal tubular acidosis, diuretic use. Phosphates are among the substances which may be lost in the Fanconi syndrome. Renal loss of phosphate may itself lead to rickets or osteomalacia.

Low in hypoparathyroidism, pseudohypoparathyroidism, vitamin D intoxication

Evaluate nephrolithiasis. Hypophosphatemia with normal serum calcium, high alkaline phosphatase, hypercalciuria, low urinary phosphorus occur with osteomalacia from excessive antacid ingestion. The relationship between serum PO4 and phosphaturia, the phosphate excretion index, is described.1 Largely, however, urine phosphate simply reflects phosphate intake in patients not on phosphate binding medications.

Children with thalassemia may have normal phosphorus absorption, but high renal phosphaturia, leading to a deficiency of phosphorus.2 Increasing dietary intake of potassium has been reported to increase serum phosphate concentrations apparently by decreasing renal excretion of phosphate.3 During the last trimester of pregnancy there is a sixfold increase in calcium and phosphorus accumulation as the fetus triples its weight. Plasma phosphorus concentrations and increased urinary phosphate may provide a useful means to assess response to phosphate supplements in the premature infant.4

1. Black DAK, Cameron JS. Renal function. In: Brown SS, Mitchell FL, Young DS, eds. Chemical Diagnosis and Disease. Amsterdam, Holland: Elsevier/North Holland; 1979:453-524.

2. Lapatsanis P, Sbyrakis S, Vertos C, Karaklis BA, Dosiadis S. Phosphaturia in thalassemia. Pediatrics. 1976 Dec; 58(6):885-892. PubMed 995519

3. Sebastian A, Hernández RE, Portale AA, Colman J, Tatsuno J, Morris RC Jr. Dietary potassium influences kidney maintenance of serum phosphorus concentration. Kidney Int. 1990 May; 37(5):1341-1349. PubMed 2345430

4. Mayne PD, Kovar IZ. Calcium and phosphorus metabolism in the premature infant. Ann Clin Biochem. 1991 Mar; 28(Pt 2):131-142. PubMed 1859151

Collection Details:

Collection Instructions:

The test request form must state date and time collection started, date and time collection finished, and urine volume. Specimens submitted without preservative should be acidified after receipt to pH <2.0 with 6N HCl.

Plastic urine container. Collect with 6N HCl.

Instruct the patient to void at 8 AM and discard the specimen. Then collect all urine including the final specimen voided at the end of the 24-hour collection period (ie, 8 AM the next morning). Screw the lid on securely. Mix well. pH must be 0 to 2.

Maintain specimen at room temperature.