A serum creatinine was found to be 6.0 mg/dL. Which of the following urea nitrogen serum results would support the same pathological condition?

A serum creatinine was found to be 6.0 mg/dL. Which of the following urea nitrogen serum results would support the same pathological condition?

• A. 6 mg/dL
• B. 20 mg/dL
• C. 35 mg/dL
• D. 70 mg/dL

Answer: (D)

When kidney function is impaired, both creatinine and urea (BUN) rise because the kidneys aren’t filtering waste properly. The pattern of how much each increases helps distinguish types of azotemia. A creatinine of 6 mg/dL signals substantial renal dysfunction. For the same condition, the BUN should be elevated but in a range that yields a BUN-to-creatinine ratio typical for intrinsic (renal) azotemia, roughly 10–20:1. Evaluating the numbers: a BUN of 6 mg/dL gives a ratio of about 1:1, which doesn’t fit the renal failure pattern. A BUN of 20 mg/dL gives a ratio around 3:1, still too low. A BUN of 35 mg/dL yields about 6:1, also too low. A BUN of 70 mg/dL results in roughly a 12:1 ratio, which aligns with intrinsic renal impairment. Thus, a BUN around 70 mg/dL best supports the same pathological condition indicated by a creatinine of 6 mg/dL.

When kidney function is impaired, both creatinine and urea (BUN) rise because the kidneys aren’t filtering waste properly. The pattern of how much each increases helps distinguish types of azotemia. A creatinine of 6 mg/dL signals substantial renal dysfunction. For the same condition, the BUN should be elevated but in a range that yields a BUN-to-creatinine ratio typical for intrinsic (renal) azotemia, roughly 10–20:1.

Evaluating the numbers: a BUN of 6 mg/dL gives a ratio of about 1:1, which doesn’t fit the renal failure pattern. A BUN of 20 mg/dL gives a ratio around 3:1, still too low. A BUN of 35 mg/dL yields about 6:1, also too low. A BUN of 70 mg/dL results in roughly a 12:1 ratio, which aligns with intrinsic renal impairment.

Thus, a BUN around 70 mg/dL best supports the same pathological condition indicated by a creatinine of 6 mg/dL.