Blood Urea Nitrogen, Body Fluid
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Serous and drain fluids: Peritoneal, abdominal drain, pleural, and thoracic drain
Disruption of the urinary tract with subsequent leakage of urine into body cavities may be considered on the differential diagnosis when body fluid effusions of unknown origin develop.(1) Metabolites such as creatinine and 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) 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.
Serous and drain fluids:
Detecting the presence of urine in body fluid specimens
Peritoneal dialysis fluid:
Assessing adequacy of peritoneal dialysis treatment protocols
For serous and drain fluids a fluid urea nitrogen to serum BUN (blood urea nitrogen) ratio above 1 is suggestive of the presence of urine in body fluids.(3)
Peritoneal dialysis fluid assessment is provided by the dialysis software.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
No significant cautionary statements
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.
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Block DB, Florkowski CM: Body fluids. In Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th edition Edited by N Rifai. Washington DC, AACC Press, 2017
2. 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
3. Manahan KJ, Fanning J: Peritoneal fluid urea nitrogen and creatinine reference values. Obstet Gynecol 1999;93:780-782