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HelpTest ID BUN Blood Urea Nitrogen (BUN), Serum
Reporting Name
Bld Urea Nitrog(BUN), SUseful For
Screening test for evaluation of kidney function
Specimen Type
SerumNecessary Information
Patient's age and sex are required.
Specimen Required
Patient Preparation: Fasting
Collection Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 0.5 mL
Collection Instructions:
1. Serum gel tubes should be centrifuged within 2 hours of collection.
2. Red-top tubes should be centrifuged and aliquoted within 2 hours of collection.
Specimen Minimum Volume
0.25 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Serum | Refrigerated (preferred) | 7 days | |
| Frozen | 365 days |
Reference Values
Males
1-17 years: 7-20 mg/dL
≥18 years: 8-24 mg/dL
Reference values have not been established for patients who are <12 months of age.
Females
1-17 years: 7-20 mg/dL
≥18 years: 6-21 mg/dL
Reference values have not been established for patients who are <12 months of age.
Day(s) and Time(s) Performed
Monday through Sunday; Continuously
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
84520
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| BUN | Bld Urea Nitrog(BUN), S | 3094-0 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| BUN | Bld Urea Nitrog(BUN), S | 3094-0 |
Clinical Information
Urea is the final degradation product of protein and amino acid metabolism. In protein catabolism, the proteins are broken down to amino acids and deaminated. The ammonia formed in this process is synthesized to urea in the liver. This is the most important catabolic pathway for eliminating excess nitrogen in the human body.
Increased blood urea nitrogen (BUN) may be due to prerenal causes (cardiac decompensation, water depletion due to decreased intake and excessive loss, increased protein catabolism, and high protein diet), renal causes (acute glomerulonephritis, chronic nephritis, polycystic kidney disease, nephrosclerosis, and tubular necrosis), and postrenal causes (eg, all types of obstruction of the urinary tract, such as stones, enlarged prostate gland, tumors).
The determination of serum BUN currently is the most widely used screening test for the evaluation of kidney function. The test is frequently requested along with the serum creatinine test since simultaneous determination of these 2 compounds appears to aid in the differential diagnosis of prerenal, renal and postrenal hyperuremia.
Interpretation
Serum blood urea nitrogen (BUN) determinations are considerably less sensitive than BUN clearance (and creatinine clearance) tests, and levels may not be abnormal until the BUN clearance has diminished to less than 50%. Clinicians frequently calculate a convenient relationship, the urea nitrogen:creatinine ratio-serum bun in mg/dL/serum creatinine in mg/dL.
For a normal individual on a normal diet, the reference interval for the ratio ranges between 12 and 20, with most individuals being between 12 and 16. Significantly lower ratios denote acute tubular necrosis, low protein intake, starvation, or severe liver disease. High ratios with normal creatinine levels may be noted with catabolic states of tissue breakdown, prerenal azotemia, high protein intake, etc. High ratios associated with high creatinine concentrations may denote either postrenal obstruction or prerenal azotemia superimposed on renal disease. Because of the variability of both the BUN and creatinine assays, the ratio is only a rough guide to the nature of the underlying abnormality. Its magnitude is not tightly regulated in health or disease and should not be considered an exact quantity.
Clinical Reference
Tietz Textbook of Clinical Chemistry. Fourth edition. Edited by CA Burtis, ER Ashwood, DE Bruns. WB Saunders Company, Philadelphia, 2006;24:801-803
Analytic Time
Same day/1 dayMethod Name
Photometric/Urease
Also available as part of an Electrolyte panel.
Forms
If not ordering electronically, complete, print, and send a Renal Diagnostics Test Request (T830) with the specimen.