Definition

• GFR stands for "glomerular filtration rate." This measurement determines how well the kidneys are able to remove waste products from the blood.
  
  

Calculation

• Formulas used to calculate a patient's glomerular filtration rate are complex. Dr. Stephen Z. Fadem, vice president of the board of directors of the American Association of Kidney Patients, explains that it is possible to estimate a patient's GFR using age, gender, race and the amount of creatinine in the blood, among other factors. Creatinine is a waste product produced when proteins are broken down in the body.
  
  

Disease Staging

• GFR is used to determine the stage of chronic kidney disease, or CKD. Kidney damage and a GFR above 90 indicate a patient has stage one CKD. Stage two is indicated by a GFR from 60 to 89, stage three is indicated by a GFR from 30 to 59 and stage four is indicated by a GFR from 15 to 29. Kidney failure, or stage five chronic kidney disease, is indicated by a GFR below 15.
  
  

Weaknesses

• When GFR is based on blood creatinine levels, the estimate may not be completely accurate. For example, patients who eat a high-protein diet have more creatinine in the blood, which can skew GFR results. Laboratory testing errors can also yield an inaccurate GFR estimate.
  
  

Further Testing

• Creatinine blood testing must be done to estimate GFR. If a patient's GFR is below normal, additional tests are performed to measure levels of sodium, potassium, phosphorus and blood urea nitrogen (BUN) in the blood.