DDx for Elevated BUN or Cr without Low GFR

Most of the time when we are consulted for an inpatient with a rising creatinine, the assumption is that the kidney is to blame. However, there is an important list of non-renal conditions which can increase either BUN or creatinine independently of low GFR.

An elevated BUN without AKI can occur in the following situations:
1. G.I. bleeding (because digested blood is a source of urea nitrogen).
2. excessive protein intake or a catabolic state.
3. steroid use.
4. TPN.
5. multiple boluses of iv albumin given.

An elevated creatinine (structure pictured above) without AKI can also occur, though less commonly than an elevated BUN without AKI. Recall that a percentage of creatinine clearance occurs via secretion; therefore, drugs which inhibit creatinine secretion such as Bactrim, probenecid, or Pepcid can increase serum creatinine without actually affecting the GFR. Furthermore, intense exercise can transiently increase the creatinine. Finally, some chemicals (e.g., nitromethane, used as a component of types of fuels and solvents) can interfere with the assay by which creatinine is detected in the laboratory.

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