What is the role of kidney function studies in the workup of acute kidney injury (AKI)?

Updated: Dec 24, 2020
  • Author: Biruh T Workeneh, MD, PhD, FASN; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Although increased levels of blood urea nitrogen (BUN) and creatinine are the hallmarks of renal failure, the rate of rise depends on the degree of renal insult and, with respect to BUN, on protein intake. BUN may be elevated in patients with gastrointestinal (GI) or mucosal bleeding, steroid treatment, or protein loading.

The ratio of BUN to creatinine is an important finding. The ratio can exceed 20:1 in conditions in which enhanced reabsorption of urea is favored (eg, in volume contraction); this suggests prerenal AKI.

Assuming that the patient has no renal function, the rise in BUN over 24 hours can be roughly predicted using the following formula:

(24-hour protein intake in milligrams × 0.16) ÷ total body water

The result is expressed in mg/dL and added to the baseline BUN value to yield the predicted BUN.

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