Assessing the kidneys' glomerular filtration rate (GFR) is a major component in evaluating renal function. The GFR is generally defined as the rate at which the kidneys filter plasma constituents through the glomerular capillary membranes into the Bowman's capsule. In other words, GFR is a measurement of how much volume of plasma is cleared or filtered in a given amount of time. GFR is typically reported in milliliters of plasma per minute (mL/min) and is corrected for body surface area. A normal value for GFR is ~125 mL/min/1.73 m2. Decreases are associated with various conditions, both benign and pathologic.
GFR is determined through one of two methods:
- Direct measurement using an infused compound
- Estimating equations using endogenous biomarkers for reference
Whichever method is used, an ideal marker for measuring (or estimating) glomerular filtration would be:
- Freely filtered at the glomerulus
- Of low molecular weight and water soluble
- Not bound by plasma proteins
- Not reabsorbed, secreted, or metabolized by kidney tubules
- Not eliminated through a process outside the kidney
