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Epic Code LAB2111178 Urea Nitrogen, Body Fluid

Additional Codes

Mayo Code: UEBF

Interface Order Alias: 10632

Cerner: 9119

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Useful For

Identifying the presence of urine as a cause for accumulation of fluid in a body compartment


Assessing adequacy of peritoneal dialysis treatment protocols

Specimen Type

Body Fluid

Necessary Information

1. Date and time of collection are required.

2. Specimen source is required.

Specimen Required

Preferred Source:

-Peritoneal fluid (peritoneal, abdominal, ascites, paracentesis)

-Pleural fluid (pleural, chest, thoracentesis)

-Drain fluid (drainage, JP drain)

-Peritoneal dialysate (dialysis fluid)


Acceptable Source: Write in source name with source location (if appropriate)

Collection Container/Tube: Sterile container

Submission Container/Tube: Plastic vial

Specimen Volume: 1 mL

Collection Instructions:

1. Centrifuge to remove any cellular material and transfer into a plastic vial.

2. Indicate the specimen source and source location on label.

Specimen Minimum Volume

0.5 mL


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

Specimen Stability Information

Specimen Type Temperature Time Special Container
Body Fluid Refrigerated (preferred) 7 days
  Frozen  30 days
  Ambient  24 hours

Reject Due To

Gross hemolysis Reject
Gross lipemia Reject
Gross icterus Reject
Cerebrospinal fluid, breast milk, saliva, nasal secretions, gastric secretions, bronchoalveolar lavage (BAL) or bronchial washings, colostomy/ostomy, feces, urine, , sputum, or vitreous fluid Reject


In very rare cases, gammopathy, in particular type IgM (Waldenstrom macroglobulinemia), may cause unreliable results.


Ammonium ions may cause erroneously elevated results.

Clinical Information

Byproducts of nitrogen metabolism are present in high concentration in urine compared to blood and serve as a surrogate marker for the identification of urine leakage into a body compartment. Concentrations of creatinine or urea nitrogen that exceed the concentration found in a concurrent sample of blood are suggestive of the presence of urine.(1)


Peritoneal, abdominal, pelvic drain fluids:

Disruption of the urinary tract with subsequent leakage of urine into body cavities may be considered as part of the differential diagnosis when body fluid effusions develop of unknown origin.(2) Metabolites such as creatinine or urea that are contained in urine at high concentrations are good candidates to measure in body fluids for this investigation. Elevated concentrations may elicit a more focused radiologic examination to identify possible bladder rupture or perforation or the development of urinary fistula, which are typically corrected by surgical intervention.


Peritoneal dialysis fluid:

Peritoneal dialysis (PD) is a type of dialysis in which hyperosmotic fluid is passed into the patient's peritoneal cavity for a prescribed dwell time, wherein the peritoneum is employed as the dialysis membrane. The dwell fluid containing waste molecules removed by dialysis is drained and replaced with fresh fluid and the process repeated. Measurements of urea, creatinine, glucose, or other electrolytes in serum, urine, and the peritoneal dialysate fluid, aid in the assessment of peritoneal membrane transport characteristics and serve as markers of dialysis adequacy. Adequacy of PD is important to monitor because patients who maintain a sufficient clearance over time have longer survival.(2) Peritoneal urea clearance volume of distribution or urea (Kt/V) is calculated to measure solute clearance from the daily peritoneal urea clearance (Kt), and the volume of distribution of urea (V). Adequacy and membrane transport characteristics are calculated by plugging in the appropriate laboratory parameters into software packages used by dialysis centers.

Method Name


Report Available

Same day/1 to 2 days

Reporting Name

Urea Nitrogen, BF

Reference Values

An interpretive report will be provided.


Peritoneal and drain fluid concentrations should be compared to serum or plasma. A fluid to serum ratio of greater than 1.0 suggests the specimen may be contaminated with urine.(1)


Peritoneal dialysate urea nitrogen concentrations can be used to calculate the adequacy of peritoneal dialysis by monitoring solute clearance over time.(3)


All other fluids: Results should be interpreted in conjunction with serum urea nitrogen and other clinical findings.

Method Description

This is a kinetic ultraviolet assay where urease cleaves urea to form ammonia and carbon dioxide. The ammonia formed then reacts with alpha-ketoglutarate and NADH in the presence of urease/glutamate dehydrogenase (GLDH) to yield glutamate and NAD. The decrease in absorbance, due to the consumption of NADH, is measured kinetically and is proportional to the amount of urea in the sample.(Package insert: Roche Urea/BUN reagent. Roche Diagnostic Corp; V7.0 07/2019)

Day(s) Performed

Monday through Sunday

Clinical Reference

1. Manahan KJ, Fanning J: Peritoneal fluid urea nitrogen and creatinine reference values. Obstet Gynecol. 1999 May;93(5 Pt 1):780-782. doi: 10.1016/s0029-7844(98)00516-x

2. Block DR, Florkowski CM: Body fluids. In: Rafai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier;2018:chap 43

3. Canada-USA (CANUSA) Peritoneal Dialysis Study Group. Adequacy of dialysis and nutrition in continuous peritoneal dialysis: association with clinical outcomes. J Am Soc Nephrol. 1996;7:198-207

Test Classification

This test has been modified from the manufacturer's instructions. Its performance characteristics were determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
UEBF Urea Nitrogen, BF 3093-2


Result ID Test Result Name Result LOINC Value
UE_BF Urea Nitrogen, BF 3093-2
FLD15 Fluid Type, Urea Nitrogen 14725-6
Laboratory Test Directory Additional Information:

Alias: BUN BFL