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HelpTest ID RTRPP Tubular Reabsorption of Phosphorus, Random
Useful For
Assessing renal reabsorption of phosphorus in a variety of pathological conditions associated with hypophosphatemia including hypophosphatemic rickets, tumor-induced osteomalacia and tumoral calcinosis
Adjusting phosphate replacement therapy in severe deficiency states monitoring the renal tubular recovery from acquired Fanconi's syndrome
Profile Information
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| RTRP | Tubular Phosp Reabsorption, Random | No | Yes |
| CTUR | Creatinine Conc | Yes, (Order CTU) | Yes |
| PHOS | Phosphorus (Inorganic), S | Yes | Yes |
| CREA2 | Creatinine, S | Yes, (Order CREAZ) | Yes |
Method Name
RTRP: Calculation
CTUR, CREA2: Enzymatic Colorimetric Assay
PHOS: Photometric, Ammonium Molybdate
Reporting Name
Tubular Phosp Reabsorption, RandomSpecimen Type
SerumUrine
Serum and urine are required.
Specimen Type: Serum
Collection Container/Tube: Red top or serum gel
Submission Container/Tube: Plastic vial
Specimen Volume: 0.5 mL
Collection Instructions:
1. Fasting.
2. Label specimen as serum.
Specimen Type: Urine
Container/Tube: Plastic, 5-mL tube (Supply T465)
Specimen Volume: 5 mL
Collection Instructions:
1. Collect a random urine specimen.
2. No preservative.
3. Label specimen as urine.
Specimen Minimum Volume
Urine: 1 mL/Serum: 0.25 mL
Specimen Stability Information
| Specimen Type | Temperature | Time |
|---|---|---|
| Serum | Frozen (preferred) | 7 days |
| Refrigerated | 7 days | |
| Urine | Refrigerated (preferred) | |
| Ambient | ||
| Frozen | ||
Clinical Information
The tubular reabsorption of phosphate (TRP) is the fraction (or percent) of filtered phosphorus that is reabsorbed by renal tubules. Its measurement is useful when evaluating patients with hypophosphatemia. In general, a reduced TRP in the presence of hypophosphatemia is indicative of a renal defect in phosphate reabsorption.
The ratio of the maximum rate of tubular phosphate reabsorption to the glomerular filtration rate (TmP/GFR) is considered the most convenient way to evaluate renal phosphate transport and is referred to as the theoretical renal phosphate threshold. This corresponds to the theoretic lower limit of plasma phosphate below which all filtered phosphate would be reabsorbed. Although direct measurements of parathyroid hormone (PTH), which increases renal phosphate excretion have replaced much of the utility of TmP/GFR measurements, it may still be useful in assessing renal reabsorption of phosphorus in a variety of pathological conditions associated with hypophosphatemia.
Reference Values
TUBULAR REABSORPTION OF PHOSPHORUS
>80%
(Although, tubular reabsorption of phosphorus levels must be interpreted in light of the prevailing plasma phosphorus and glomerular filtration rate.)
TUBULAR MAXIMUM PHOSPHORUS REABSORPTION/GLOMERULAR FILTRATION RATE (TmP/GFR)
2.6-4.4 mg/dL (0.80-1.35 mmol/L)
PHOSPHORUS (INORGANIC)
Males
1-4 years: 4.3-5.4 mg/dL
5-13 years: 3.7-5.4 mg/dL
14-15 years: 3.5-5.3 mg/dL
16-17 years: 3.1-4.7 mg/dL
≥18 years: 2.5-4.5 mg/dL
Reference values have not been established for patients that are <12 months of age.
Females
1-7 years: 4.3-5.4 mg/dL
8-13 years: 4.0-5.2 mg/dL
14-15 years: 3.5-4.9 mg/dL
16-17 years: 3.1-4.7 mg/dL
≥18 years: 2.5-4.5 mg/dL
Reference values have not been established for patients that are <12 months of age.
CREATININE
Males
12-24 months: 0.1-0.4 mg/dL
3-4 years: 0.1-0.5 mg/dL
5-9 years: 0.2-0.6 mg/dL
10-11 years: 0.3-0.7 mg/dL
12-13 years: 0.4-0.8 mg/dL
14-15 years: 0.5-0.9 mg/dL
≥16 years: 0.8-1.3 mg/dL
Reference values have not been established for patients that are <12 months of age.
Females
12-36 months: 0.1-0.4 mg/dL
4-5 years: 0.2-0.5 mg/dL
6-8 years: 0.3-0.6 mg/dL
9-15 years: 0.4-0.7 mg/dL
≥16 years: 0.6-1.1 mg/dL
Reference values have not been established for patients that are <12 months of age.
Cautions
No significant cautionary statements
Day(s) Performed
Monday through Sunday; Continuously
Report Available
Same day/1 dayPerforming Laboratory
Mayo Medical Laboratories in Rochester
Test Classification
This test has been cleared or approved 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
82565-Creatinine
84100-Phosphorus inorganic (phosphate), serum
84105-Phosphorus inorganic (phosphate), urine