A technologist obtains a urea N value of 61 mg/dL and a serum creatinine value of 2.5 mg/dL on a patient. These results indicate

A technologist obtains a urea N value of 61 mg/dL and a serum creatinine value of 2.5 mg/dL on a patient. These results indicate

• A. Congestive heart failure
• B. Dehydration
• C. Glomerular nephritis
• D. Urinary tract obstruction

Answer: (B)

The key idea is how the kidney’s response to reduced blood flow shows up in the BUN (urea nitrogen) relative to creatinine. When volume depletion or dehydration lowers renal perfusion, the kidneys reabsorb more urea from the filtrate, so the BUN rises disproportionately compared with creatinine. Here, the BUN is 61 mg/dL and the creatinine is 2.5 mg/dL, giving a BUN/creatinine ratio of about 24.4. A ratio above about 20 strongly points to prerenal azotemia from decreased renal perfusion, with dehydration being the classic cause. In intrinsic renal disease (like glomerulonephritis) the ratio tends to be closer to normal because the problem is within the kidney itself rather than reduced blood flow, and postrenal causes can show variable ratios. So the pattern here—a markedly elevated BUN with a disproportionately elevated ratio to creatinine—best fits dehydration.

The key idea is how the kidney’s response to reduced blood flow shows up in the BUN (urea nitrogen) relative to creatinine. When volume depletion or dehydration lowers renal perfusion, the kidneys reabsorb more urea from the filtrate, so the BUN rises disproportionately compared with creatinine. Here, the BUN is 61 mg/dL and the creatinine is 2.5 mg/dL, giving a BUN/creatinine ratio of about 24.4. A ratio above about 20 strongly points to prerenal azotemia from decreased renal perfusion, with dehydration being the classic cause. In intrinsic renal disease (like glomerulonephritis) the ratio tends to be closer to normal because the problem is within the kidney itself rather than reduced blood flow, and postrenal causes can show variable ratios. So the pattern here—a markedly elevated BUN with a disproportionately elevated ratio to creatinine—best fits dehydration.