How is GFR estimated in routine clinical practice?
GFR is usually estimated using the serum creatinine and an estimating equation.
Serum creatinine is the most common endogenous filtration marker. Endogenous filtration markers are markers produced by the body but are filtered by the glomerulus.
All endogenous filtration markers are not perfect filtration markers in that there are non-GFR determinants of their levels in the blood, in particular, variation in generation (i.e., production) among people, secretion, or reabsorption by the tubule or extrarenal elimination.
Estimating equations combine endogenous filtration marker(s), such as creatinine and cystatin C, with other variables, such as age, gender, race, and body size, as surrogates for non-GFR determinants of the filtration markers, and therefore can overcome some of the limitations of the filtration marker alone.
An estimating equation is derived using regression techniques to model the observed relationship between the serum level of the marker and measured GFR in a study population.
