Massive and disproportionate elevation of blood urea nitrogen in acute azotemia.

In renal failure, blood urea nitrogen and serum creatinine usually rise in tandem; the normal BUN: Cr ratio is 10-15: 1. Disproportionate rises in BUN: Cr (> 20: 1) often imply pre-renal azotemia but may be caused by increased protein catabolism or an excessive protein load. In this study we looked at intensive care patients who acutely developed markedly increased BUN (> or = 100 mg/dL) with only modest elevation of Cr (< or = 5 mg/dL) for possible causes of the disproportionate azotemia.