An eGFR of 59 is slightly below normal, according to the American Kidney Fund. A lower-than-normal GFR sometimes indicates a loss of kidney function. People with kidney failure have very low eGFR values.
Estimated glomerular filtration rate is a calculation used to assess how well the kidneys are working, explains the American Kidney Fund. The eGFR value is based on the results of the blood test for creatinine, a waste product filtered out of the blood by the kidneys. A laboratory calculates eGFR using the person's serum creatinine level, age, gender and race. An eGFR above 60 milliliters per minute per 1.73 meters squared is normal.
A person with an eGFR less than 60 should consult with a doctor, advises the American Kidney Fund. Having another test in a few months can help determine if the kidneys are damaged or if the decreased eGFR was the temporary result of another condition. If eGFR is still low after 3 months, additional tests may be necessary to determine if the kidneys are working properly.
The eGFR test is recommended for people who have been diagnosed with chronic kidney disease, states MedlinePlus. People with an increased risk of kidney disease should also have the test. Diabetes, high blood pressure, heart disease, frequent urinary tract infections and urinary blockages increase the risk for developing kidney disease.