Test ID: NITU
Nitrogen, Total, Urine
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 nutritional status (protein malnutrition)
Evaluating protein catabolism
Determining nitrogen balance, when used in conjunction with 24-hour fecal nitrogen measurement
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
Method Name A short description of the method used to perform the test
Dumas Combustion
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Aliases Lists additional common names for a test, as an aid in searching
Total Urinary Nitrogen
TUN
Specimen Type Describes the specimen type needed for testing
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.
Container/Tube: Plastic, 10-mL urine tube (Supply T068)
Specimen Volume: 10 mL
Collection Instructions:
1. 24-Hour volume is required.
2. Collect urine for 24 hours.
3. No preservative.
Additional Information: See Urine Preservatives in Special Instructions for multiple collections.
Urine Preservative Collection Options
| Ambient | Yes |
| Refrigerated | Yes |
| Frozen | Preferred |
| 6N HCl | Yes |
| 50% Acetic Acid | Yes |
| Na2CO3 | Yes |
| Toluene | Yes |
| 6N HNO3 | No |
| Boric Acid | No |
| Thymol | Yes |
Forms: If not ordering electronically, submit a General Request Form (Supply T239) with the specimen.
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 |
|---|---|---|
| Urine | Refrigerated (preferred) | 7 days |
| Ambient | 7 days | |
| Frozen | ||
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Nitrogen is a key component of proteins. During protein catabolism (proteolysis), nitrogen is excreted in the urine and feces. Protein catabolism may be increased after stress (eg, physical trauma, surgery, infections, burns).
"Nitrogen balance" is the difference between the amount of nitrogen ingested and the amount excreted. A patient who is in negative nitrogen balance is using muscle protein to meet the metabolic requirements of the body and is, therefore, in a catabolic state.
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.
<16 years: not established
> or =16 years: 4-20 g/24 hours
Interpretation Provides information to assist in interpretation of the test results
Twenty-four hour urinary nitrogen excretion levels within the normal range are indicative of adequate nutrition. Slightly abnormal excretion rates may be a result of moderate stress or complications such as infection or trauma. Significantly abnormal excretion rates may be associated with severe stress due to multiple trauma, head injury, sepsis, or extensive burns. The goal with therapy for a depleted person is a positive nitrogen balance of 4 to 6 g nitrogen/24 hours.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Measurement of both urine and fecal nitrogen is necessary for the accurate determination of nitrogen balance.
During nitrogen balance studies, nitrogen lost from exuding wounds, such as burns, and from copious sputum must be included in the patient's evaluation.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Phinney SD: The assessment of protein nutrition in the hospitalized patient. Clin Lab Med 1981;1:767-774
2. Veldee MS: Nutritional assessment, therapy, and monitoring. In Tietz Textbook of Clinical Chemistry. Third edition. Edited by CA Burtis, ER Ashwood. Philadelphia, WB Saunders Company, 1999, pp 1385-1386
3. Konstantinides FN, Kostantinides NN, Li JC, et al: Urinary urea nitrogen: too insensitive for calculating nitrogen balance studies in surgical clinical nutrition. J Parenter Enteral Nutr 1991;15:189-193
Method Description Describes how the test is performed and provides a method-specific reference
The Nitrogen analyzer utilizes the Dumas combustion method of determining total nitrogen in urine. 0.5 mL of urine is added to 0.1 grams of sucrose in a tin capsule, which is blanked with oxygen prior to hermetic sealing to exclude atmospheric nitrogen interference. The capsule is then placed in the instrument, combusted, and oxidized at 960 degrees C. Nitrogen in the form of nitric oxide is released from the specimen and is carried by carbon dioxide through a column containing tungsten that reduces the nitric oxide to molecular nitrogen. Nitrogen is detected using a thermal conductivity detector and response is compared to standards of known nitrogen concentration for quantitation. Complete analysis time is 4.0 minutes per specimen.(Ward JN, Kloke KM, Chezick PA, et al: Rapid accurate quantitation of nitrogen in urine and feces using the Elementar Rapid NIII analyzer. Clin Chem 2002;48[S6]:A71)
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, Wednesday, Friday; 8 a.m.
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.
Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result
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.
84999 (See CPT Coding in Special Instructions)
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 |
|---|---|---|
| DUR8 | Collection Duration | 13362-9 |
| TOTV | Specimen Volume | 28009-9 |
| 17418 | Nitrogen, Total, U | 2660-9 |
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