Plasma urea / creatinine ratio of 20:1 may be seen in-
Background. A blood urea nitrogen (BUN)/creatinine ratio (BCR) >20 (0.081 in international unit) is used to distinguish pre-renal azotemia (PRA) and acute tubular necrosis (ATN). However, there is little evidence that BCR can distinguish between these two conditions and/or is clinically useful Ref Harrison20th edition pg 299
Rhabdomyolysis
Ureteric calculi
Pre-renal failure
Chronic glomerulonephritis
Kidney