After rehydration, creatinine levels typically do what?

• A. Increase
• B. Decrease
• C. Remain unchanged
• D. Fluctuate

Answer: (B)

Hydration status directly affects kidney filtration. Creatinine is a waste product filtered by the kidneys, so when someone is dehydrated, reduced blood flow to the kidneys lower the glomerular filtration rate, causing serum creatinine to rise. Rehydration increases circulating volume and renal perfusion, boosting GFR and allowing more creatinine to be cleared. As a result, serum creatinine typically decreases after rehydration, especially if the elevated level was due to a temporary prerenal issue rather than intrinsic kidney damage. If kidney damage is present, the drop may be less pronounced, but the general trend with proper fluids is a reduction in creatinine.