In chronic kidney disease, what happens to GFR and serum creatinine as kidney function declines?

• A. GFR increases and creatinine decreases
• B. GFR decreases and creatinine increases
• C. GFR stays the same, creatinine stays the same
• D. GFR increases and creatinine increases

Answer: (B)

The main concept is the inverse relationship between kidney filtration capacity and serum creatinine in CKD. When nephron loss lowers the glomerular filtration rate, less plasma is filtered each minute. Creatinine is produced at a nearly constant rate and cleared mainly by filtration, so a fall in GFR means creatinine is cleared less efficiently and accumulates in the blood. The result is a decline in GFR accompanied by an increase in serum creatinine as kidney function worsens. The other patterns— GFR rising with creatinine falling, both staying the same, or both rising—do not fit how kidney function changes in CKD.