Low kidney function means that a person's kidneys are not filtering blood as well as they should be. A person with low kidney function is at risk for kidney disease, according to the National Kidney Foundation.
The glomerular filtration rate, or GFR, calculates kidney function by combining blood test results, age, race, gender and other factors. The blood test to determine a GFR calculates the level of creatinine, a waste product, in the blood, according to WebMD. A creatinine clearance test checks for creatinine in the blood and urine and is also frequently used to determine GFR.
A GFR rate less than 60 is a warning sign of kidney disease, according to the National Kidney Foundation. Other warning signs include high blood pressure, blood and protein in the urine, a creatinine and Blood Urea Nitrogen (BUN) blood test that falls outside the normal range, more frequent, difficult or painful urination, the swelling of hands and feet and puffiness around the eyes.
The National Kidney foundation defines chronic kidney disease as the presence of some kind of kidney abnormality or marker, such as protein in the urine, or decreased kidney function for three months or longer. High blood pressure and diabetes are common causes for kidney disease. Some kidney conditions run in the family while others are congenital, stemming from an abnormality at birth.