Question:
A plasma urea to creatinine ratio of 20:1 may be seen in:
A plasma urea to creatinine ratio of 20:1 may be seen in:
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A wide urea to creatinine gap means urea is being reabsorbed, the signature of underperfusion.
Updated On: Jun 24, 2026
- Rhabdomyolysis
- Ureteric calculi
- Pre-renal failure
- Chronic glomerulonephritis
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The Correct Option is C
Solution and Explanation
Step 1: A normal urea to creatinine ratio is roughly 10:1 to 15:1. A high ratio of about 20:1 points to a pre-renal cause of azotaemia.
Step 2: In pre-renal failure the kidney is underperfused (dehydration, blood loss, heart failure). Renal blood flow falls, so the tubules slow the filtrate and reabsorb more water and urea. Urea is reabsorbed along with sodium and water, but creatinine is not reabsorbed. As a result blood urea rises out of proportion to creatinine, lifting the ratio to 20:1 or higher. This makes option C correct.
Step 3: Why the others are wrong. Option A, rhabdomyolysis, releases large amounts of creatine and creatinine from damaged muscle. Creatinine rises sharply, so the urea to creatinine ratio actually falls (a low ratio), not rises.
Step 4: Option B, ureteric calculi causing obstruction, is a post-renal cause. Both urea and creatinine accumulate together, so the ratio stays near normal rather than rising to 20:1.
Step 5: Option D, chronic glomerulonephritis, is an intrinsic renal disease. Both substances are retained roughly in parallel, keeping the ratio close to the normal range.
Step 6: Only pre-renal failure selectively raises urea and gives a 20:1 ratio.
Answer: Option C.
Step 2: In pre-renal failure the kidney is underperfused (dehydration, blood loss, heart failure). Renal blood flow falls, so the tubules slow the filtrate and reabsorb more water and urea. Urea is reabsorbed along with sodium and water, but creatinine is not reabsorbed. As a result blood urea rises out of proportion to creatinine, lifting the ratio to 20:1 or higher. This makes option C correct.
Step 3: Why the others are wrong. Option A, rhabdomyolysis, releases large amounts of creatine and creatinine from damaged muscle. Creatinine rises sharply, so the urea to creatinine ratio actually falls (a low ratio), not rises.
Step 4: Option B, ureteric calculi causing obstruction, is a post-renal cause. Both urea and creatinine accumulate together, so the ratio stays near normal rather than rising to 20:1.
Step 5: Option D, chronic glomerulonephritis, is an intrinsic renal disease. Both substances are retained roughly in parallel, keeping the ratio close to the normal range.
Step 6: Only pre-renal failure selectively raises urea and gives a 20:1 ratio.
Answer: Option C.
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