Creatinine, Body Fluid
Identifying the presence of urine as a cause for accumulation of fluid in a body compartment
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
By-products of nitrogen metabolism are elevated in high concentration in urine compared to blood, and serve as a surrogate marker for the identification of urine leakage into a body compartment. This may occur due to trauma, abdominal or pelvic surgery, and bladder perforation. (1,2) Concentrations of creatinine or urea nitrogen that exceed the concentration found in a concurrent sample of blood are suggestive of the presence of urine.(1,3)
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.
Body fluid to serum ratios >1.0 suggest the presence of urine in the sample.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Specimens with total bilirubin values >20 mg/dL may see decreased values. Protein, glucose, ascorbic acid, a-ketoacids, and some cephalosporin antibiotics may interfere with the creatinine assay, causing an overestimation.
Results can be falsely decreased in patients with elevated levels of N-acetyl-p-benzoquinone imine (NAPQI, a metabolite of acetaminophen), N-acetylcysteine (NAC), and Metamizole.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Manahan KJ, Fanning J: Peritoneal fluid urea nitrogen and creatinine reference values. Obstet Gynecol 1999;93:780-782
2. Wong MH, Lim SK, Ng KL, Ng KP: Pseudo-acute kidney injury with recurrent ascites due to intraperitoneal urine leakage. Intern Med J 2012;42:848-849
3. Nguyen-Khac E, Thevenot T, Capron D, et al: Are ascitic electrolytes usable in cirrhotic patients? Correlation of sodium, potassium, chloride, urea, and creatinine concentrations in ascitic fluid and blood. Eur J Intern Med 2008;19:613-618