A markedly elevated blood creatinine value most likely indicates which of the following about kidney function?

• A. Normal function
• B. Reduced function
• C. Increased function
• D. No change in function

Answer: (B)

A markedly elevated blood creatinine value signals reduced kidney function. Creatinine is a waste product produced at a relatively constant rate and is cleared from the blood mainly by the kidneys through glomerular filtration. When the kidneys’ filtration ability declines, creatinine is not cleared as efficiently and accumulates in the blood, so the serum level rises. Because production is steady, a high creatinine is best interpreted as decreased clearance and a lower GFR, rather than increased production. If kidney function were normal, creatinine would be within the normal range; an increase in function is not how creatinine behaves, and no change in function would not cause a rise.