Glomerular filtration rate (GFR) is a measurement of the amount of glomerular filtrate (a substance similar to blood plasma but without proteins) formed in the kidneys each minute. It is used to evaluate the kidneys’ ability to remove waste products from the body.

GFR is used to screen for early signs of kidney damage and, in those already diagnosed with kidney disease (nephropathy), signs of further deterioration of kidney function. Early detection of kidney disease is important because it increases a person’s chance of preventing or delaying the progression of the disease. In those already diagnosed, detecting further deterioration can help a physician determine the stage of kidney disease. This information is then used to make decisions about treatment.

In people with diabetes, hyperglycemia (high blood sugar) and high blood pressure can damage the filtering system of the kidneys and cause kidney disease. As a result, waste products begin to accumulate in the blood and proteins and red blood cells the body could use are lost in urine. A GFR measurement may be ordered when a waste product called creatinine is detected in the blood or when protein is detected in the urine (proteinuria).

The American Heart Association recommends that people who have or are at risk for cardiovascular disease consider GFR testing because kidney disease is a major risk factor for diseases of the heart and blood vessels.

GFR cannot be directly measured. Instead, it is estimated from the measurements of other body waste products. These measurements may include:

• Cystatin C test
• Serum creatinine test
• Creatinine clearance test
• Prediction equations

The most widely used methods of estimating GFR involve urine collection and a blood sample. Patients may need to make certain preparations (e.g., dietary and medication changes) beforehand. Certain factors (e.g., age, sex, diet, amount of muscle mass) can affect test results and therefore should be taken into consideration.

If kidney damage is detected, patients are advised to see a nephrologist (a physician who specializes in kidneys). If kidney failure is present, treatment may include dialysis or a kidney transplant.