During severe dehydration, because blood pressure lowers and kidney function is reduced, the glomerular filtration rate (GFR), declines. When rehydration occurs, GFR normalizes, unless there has been some kidney damage. Mild dehydration normally does not affect GFR.
According to MedlinePlus, a service of the U.S. National Library of Medicine, GFR is a test used to assess kidney function. It calculates how much blood filters through the kidneys each minute. To determine GFR, a lab specialist first tests the creatinine level in a blood sample. The result of this test is combined with a number of other factors, including age, gender, ethnicity, height and weight, to calculate a patient's GFR.
A patient who has a GFR of 60 or higher is considered in the normal range. If the GFR is below 60, kidney disease is a possibility. Treatment may include lifestyle changes, dietary adjustment, avoiding certain medicines and taking other medicines. Further tests indicate whether or not dialysis is needed. A GFR of 15 or under indicates kidney failure, and the patient probably needs either dialysis or a kidney transplant. It is not possible to raise a low GFR, but certain steps can be taken to prevent it from going lower. These include keeping blood pressure and cholesterol levels normal, cutting back on salt, limiting intake of alcoholic drinks, losing weight, quitting smoking, exercising regularly and eating heart-healthy foods.