Overview of Urea and Creatinine

Jose H. Salazar, MS, MLS(ASCP)CM

Disclosures

Lab Med. 2014;45(1):e19-e20. 

In This Article

Clinical Significance

The measurement of creatinine concentrations in plasma and urine samples illustrates the filtration capacity of the glomerulus, also known as the glomerular filtration rate (GFR.) Creatinine is produced endogenously within the body and is freely filtered by the glomerulus. These characteristics make creatinine a useful endogenous marker for creatinine clearance. If the GFR is decreased, as is in renal disease, creatinine clearance via the renal system is compromised. The reduced GFR will then lead to an increase in plasma creatinine concentration. The measurement of plasma alone should not be used to assess renal function. Plasma creatinine levels may not be affected until significant renal damage has occurred. In addition, a plasma creatinine level that is within normal reference range does not equate to a normal functioning renal system.[3]

Although not as specific as creatinine, BUN can also be used as an indicator of renal function. BUN is not the preferred marker for clearance because it is influenced by factors such as a high protein diet, variables in protein synthesis, and patient hydration status. Alone BUN is not the ideal marker for GFR. Combined with plasma creatinine as a creatinine/BUN ratio, BUN can be a useful analyte in differentiating pre or post renal increase of plasma NPNs.[4]

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