The ideal substance for the measurement of glomerular is one that is:
- freely filtered, i.e. neither reabsorbed or secreted
- not metabolised or produced by the kidney
- must not alter GFR
Experimentally, synthetic compounds like inulin are used (a polyfructose molecule with Mr 5000). Clinically, creatinine clearance is used. Although by no means perfect, it is produced at a relatively constant rate by body muscle.
see also Estimated GFR (EGFR)