GFR

GFR as a measure for kidney function

GFR (glomerular filtration rate) is equal to the total of the filtration rates of the functioning nephrons in the kidney. GFR is considered the optimal way to measure kidney function, which in conjunction with albuminuria, can help determine the extent of CKD in an individual. The level of GFR and its magnitude of change over time are vital to:

• the detection of kidney disease
• understanding its severity (categories)
• making decisions about diagnosis, prognosis and treatment
• detection of CKD progression

A rise in blood creatinine levels is observed only after significant loss of functioning nephrons. A better way to measure kidney function is to estimate GFR with equations that use serum creatinine levels and some or all of the following variables: gender, age, weight, and race.

Normal GFR varies according to age, sex, and body size; in young adults it is approximately 120 ml/min/1.73 m² and declines in normal individuals with age. However, a decrease in GFR may also be a marker of kidney disease and precedes the onset of kidney failure; therefore a persistently reduced GFR is a specific diagnostic criterion for CKD. Below 60 ml/min/1.73 m², the prevalence of complications of CKD increases, as does the risk of cardiovascular disease (CVD). This is a 50% reduction in GFR relative to that of a young adult.

Measuring GFR

The gold standard for measuring GFR is using plasma or urinary clearance of an exogenous filtration marker. However, this is a complex procedure and generally not routinely performed. Therefore, GFR is usually estimated from the person's serum creatinine and/or cystatin C level, in combination with demographic factors such as age, race, and gender using an estimating equation.

• Use serum creatinine with age, gender, and race in the recommended CKD-EPI creatinine equation (2009).
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• Use confirmatory tests in specific circumstances when eGFR based on serum creatinine is less accurate:
  • Cystatin C-based equations
  • Creatinie and Cystatin C-based equations
  • Measured GFR

The following chart lists the GFR categories in CKD, in addition to clinical presentations associated with each category.

Calculating GFR on Smartphone and Online

• To download NKF's free GFR calculator to your smartphone: www.kidney.org/apps
• To use the free GFR calculator on the NKF website: www.kidney.org/gfr

More information on GFR

• For more information on GFR and estimating equations, visit: http://www.kidney.org/professionals/kdoqi/gfr.cfm