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Test ID: RPOU    
Phosphorus, Pediatric, Random, Urine

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

Evaluation of hypo- or hyperphosphatemic states

 

Evaluation of patients with nephrolithiasis

 

A timed 24-hour urine collection is the preferred specimen for measuring and interpreting this urinary analyte. Random collections normalized to urinary creatinine may be of some clinical use in patients who cannot collect a 24-hour specimen, typically small children. Therefore, this random test is offered for children <16 years old.

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 that 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 that 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.

No established reference values

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.

 

Pediatric Reference Ranges on a Random Specimen Phosphate/Creatinine (mg/mg)

Age (year)

5th Percentile

95th Percentile

0-1

>0.34

<5.24

1-2

>0.34

<3.95

2-3

>0.34

<3.13

3-5

>0.33

<2.17

5-7

>0.33

<1.19

7-10

>0.32

<0.97

10-14

>0.22

<0.86

14-17

>0.21

<0.75

 

Matos V, van Melle G, Boulat O et al:  Urinary phosphate/creatinine, calcium/creatinine, and magnesium/creatinine ratios in a healthy pediatric population. J Pediatr 1997;131:252-257

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