Test ID: RTRPP
Tubular Reabsorption of Phosphorus, Random
Secondary ID 
A test code used for billing and in test definitions created prior to November 2011
NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.
Useful For Suggests clinical disorders or settings where the test may be helpful
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 A profile is a group of laboratory tests that are ordered and performed together under a single Mayo Test ID. Profile information lists the test performed, inclusive of the test fee, when a profile is ordered and includes reporting names and individual availability.
| 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 A short description of the method used to perform the test
RTRP/26605: Calculation
CTUR/24017, CREA2/28266: Enzymatic Colorimetric Assay
PHOS/8408: Photometric, Ammonium Molybdate
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Specimen Type Describes the specimen type needed for testing
Urine
Specimen Required Defines the optimal specimen. This field describes the type of specimen required to perform the test and the preferred volume to complete testing. The volume allows automated processing, fastest throughput and, when indicated, repeat or reflex testing.
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, 6-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 Defines the amount of specimen required to perform an assay once, including instrument and container dead space. Submitting the minimum specimen volume makes it impossible to repeat the test or perform confirmatory or perform reflex testing. In some situations, a minimum specimen volume may result in a QNS (quantity not sufficient) result, requiring a second specimen to be collected.
Reject Due To Identifies specimen types and conditions that may cause the specimen to be rejected
| Hemolysis | NA |
| Lipemia | NA |
| Icterus | NA |
| Other | NA |
Specimen Stability Information Provides a description of the temperatures required to transport a specimen to the laboratory. Alternate acceptable temperature(s) are also included.
| Specimen Type | Temperature | Time |
|---|---|---|
| Serum | Frozen (preferred) | 7 days |
| Refrigerated | 7 days | |
| Urine | Refrigerated (preferred) | |
| Ambient | ||
| Frozen | ||
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
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 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.
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
> or =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
> or =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
> or =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
> or =16 years: 0.6-1.1 mg/dL
Reference values have not been established for patients that are <12 months of age.
Interpretation Provides information to assist in interpretation of the test results
Interpretation of tubular reabsorption of phosphate (TRP) and TmP/GMR is dependent upon the clinical situation, and should be interpreted in conjunction with the serum phosphorous concentration.
TmP/glomerular filtration rate (GFR) is independent of dietary phosphorus intake, tissue release of phosphorus, and GFR.
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
1. Suki WN, Lederer ED, Rouse D: Renal transport of calcium, magnesium, and phosphate. In The Kidney, 6th edition, Edited by B Brenner. WB Saunders Company, 2000, Chapter 12
2. Bijvoet OL: Relation of plasma phosphate concentration to renal tubular reabsorption of phosphate. Clin Sci 1969;37:23-36
3. Walton RJ, Bijvoet OL: Nomogram for derivation of renal threshold phosphate Concentration. Lancet 1975;2:309-310
4. Payne RB: Renal tubular reabsorption of phosphate (TmP/GFR): indications and interpretation. Ann Clin Biochem 1998;35:201-206
Method Description Describes how the test is performed and provides a method-specific reference
Creatinine is performed by the enzymatic method, which is based on the determination of sarcosine from creatinine with the aid of creatininase, creatinase, and sarcosine oxidase. The liberated hydrogen peroxide is measured via a modified Trinder reaction using a colorimetric indicator. Optimization of the buffer system and the colorimetric indicator enables the creatinine concentration to be quantified both precisely and specifically. (Package insert: Roche Diagnostics, Indianapolis IN, 2004)
In the phosphorus assay, inorganic phosphorus reacts with ammonium molybdate in an acidic solution to form ammonium phosphomolybdate, which is quantified in the ultraviolet range (340nm). (Package insert: Roche Phosphorus, Roche Diagnostic Corp, Indianapolis, IN)
Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
Monday through Sunday; Continuously
Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.
Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location The location of the laboratory that performs the test
Test Classification Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer's instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR), Investigation Use Only (IUO) product, or a Research Use Only (RUO) product.
CPT Code Information Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Medical Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
82565-Creatinine
84100-Phosphorus inorganic (phosphate), serum
84105-Phosphorus inorganic (phosphate), urine
LOINC® Code Information Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the result codes returned for this test or profile.
| Result ID | Reporting Name | LOINC Code |
|---|---|---|
| CREA2 | Creatinine, S | 2160-0 |
| CTUR | Creatinine Conc | 35674-1 |
| PHOS | Phosphorus (Inorganic), S | 2777-1 |
| TRA | TRP | In Process |
| GFRR | Random TmP/GFR | In Process |
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