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Test Catalog

Test ID: POU    
Phosphorus, 24 Hour, Urine

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

Evaluation of hypo- or hyper-phosphatemic states


Evaluation of patients with nephrolithiasis

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Approximately 80% of filter phosphorous is reabsorbed by renal proximal tubule cells. The regulation of urinary phosphorous excretion is principally dependent on regulation of proximal tubule phosphorous reabsorption. A variety of factors influence renal tubular phosphate reabsorption, and consequent urine excretion. Factors which increase urinary phosphorous excretion include high phosphorous diet, parathyroid hormone, extracellular volume expansion, low dietary potassium intake and proximal tubule defects (eg, Fanconi Syndrome, X-linked hypophosphatemic Rickets, tumor-induced osteomalacia). Factors which decrease, or are associated with decreases in, urinary phosphorous excretion include low dietary phosphorous intake, insulin, high dietary potassium intake, and decreased intestinal absorption of phosphorous (eg, phosphate-binding antacids, vitamin D deficiency, malabsorption states).


A renal leak of phosphate has also been implicated as contributing to kidney stone formation in some patients.

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.

<1,100 mg/specimen 

Interpretation Provides information to assist in interpretation of the test results

Interpretation of urinary phosphorous excretion is dependent upon the clinical situation, and should be interpreted in conjunction with the serum phosphorous concentration.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

No significant cautionary statements

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

Agarwal R, Knochel JP: Hypophosphatemia and hyperphosphatemia. In The Kidney. Sixth edition. Edited by Barry M Brenner. WB Saunders Company, Philadelphia, PA, 2000, pp 1071-1125

Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test