Localization of azotemia: Test your skill
Feb 01, 2005
Azotemia is defined as an abnormal concentration of urea, creatinine, and other nonprotein nitrogenous substances in blood, plasma or serum.
Azotemia is a laboratory finding with several fundamentally different causes. Since nonprotein nitrogenous compounds (including urea and creatinine) are endogenous substances, abnormal concentrations in serum may be caused by
However, azotemia may be caused by factors that are not directly related to the urinary system and by abnormalities of the lower urinary tract not directly related to the kidney. Therefore, azotemia should not be used as a synonym for primary renal failure or uremia.Although the concentrations of serum urea nitrogen and creatinine commonly are used as crude indices of glomerular filtration rate, meaningful interpretation of these endogenous markers depends on recognition and evaluation of prerenal, primary renal, and post-renal factors that influence their rate of production and their rate of loss. In addition, knowledge of urine specific gravity values is of great significance in localizing different types of azotemia. If sufficient clinical evidence is present to warrant examination of a patient's renal function by determining the serum concentration of creatinine or urea nitrogen, then the pretreatment specific gravity of urine should be routinely evaluated at the same time.
My interpretations are summarized at the end of this Diagnote. The following discussion summarizes basic mechanisms associated with different types and combinations of azotemia associated with impaired excretion of urea and creatinine. It does not include non-urinary factors that may result in mild increases in the rate of production of these metabolites (consumption of high-protein diets, gastrointestinal hemorrhage).