**Core Concept**
A disproportionately high blood urea level relative to serum creatinine (urea:creatinine ratio >20:1) reflects increased urea production or impaired urea clearance, commonly seen in conditions with reduced renal perfusion or volume depletion. This ratio is a key indicator of prerenal or congestive conditions, not intrinsic renal disease.

**Why the Correct Answer is Right**
In intrinsic renal failure, the kidney's functional damage affects glomerular filtration and tubular function uniformly, leading to a rise in both urea and creatinine, but with a **normal or low urea:creatinine ratio** (typically 20:1 strongly suggests prerenal or congestive causes, not intrinsic renal failure. In intrinsic renal disease, the ratio remains low or normal due to uniform impairment of both urea and creatinine clearance.

✓ Correct Answer: C. Intrinsic renal failure