Internal Medicine

Populations who are Difficult to Estimate
Certain patient groups have dramatically different serum creatinine production or elimination compared to the normal patient population. The following groups are notoriously difficult to estimate true renal function:

Amputation - Falsely low serum creatinine due to less production from muscle mass
Burn injury - Increased GFR
Cirrhosis - Falsely low serum creatinine due to less muscle mass and reduced hepatic conversion of creatine to creatinine
Cystic fibrosis - Increased GFR
Muscle disorders - Muscular dystrophy and other muscle disorders that can cause cachexia
Pregnancy - Difficult to estimate lean body mass, increased GFR
Unstable renal function - Equations used to estimate unstable renal function are very old and not validated in a large patient population