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Test ID RPOU Phosphorus, Pediatric, Random, Urine

Reporting Name

Phosphorus, Pediatric, Random, U

Useful For

Evaluation of hypo- or hyperphosphatemic states

 

Evaluation of patients with nephrolithiasis

Specimen Type

Urine


Specimen Required


Container/Tube: Plastic, 5-mL tube (T465)

Specimen Volume: 4 mL

Collection Instructions:

1. Collect a random urine specimen.

2. No preservative.

Additional Information: 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.


Specimen Minimum Volume

1 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Urine Refrigerated (preferred) 14 days
  Frozen  14 days
  Ambient  7 days

Reference Values

No established reference values

Day(s) and Time(s) Performed

Monday through Sunday

Test Classification

This test has been cleared, approved or is exempt by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information

84105

LOINC Code Information

Test ID Test Order Name Order LOINC Value
RPOU Phosphorus, Pediatric, Random, U 11141-9

 

Result ID Test Result Name Result LOINC Value
POCON Phosphorus, Pediatric, Random, U 2778-9
CREA6 Creatinine Concentration 2161-8
RATO5 Phosphorus/Creatinine Ratio 11141-9

Clinical Information

Approximately 80% of filter phosphorus is reabsorbed by renal proximal tubule cells. The regulation of urinary phosphorus excretion is principally dependent on regulation of proximal tubule phosphorus reabsorption. A variety of factors influence renal tubular phosphate reabsorption, and consequent urine excretion. Factors that increase urinary phosphorus excretion include high phosphorus 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 phosphorus excretion include low dietary phosphorus intake, insulin, high dietary potassium intake, and decreased intestinal absorption of phosphorus (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.

 

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.

Interpretation

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)(1)

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

 

Clinical Reference

1. 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

2. 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

Analytic Time

1 day

Method Name

Molybdic Acid

Forms

If not ordering electronically, complete, print, and send a Renal Diagnostics Test Request (T830) with the specimen.