Kidney blood levels may need to be tested in order to determine the level of creatinine in the blood, explains the National Kidney Foundation. The amount of creatinine in the blood evaluates kidney function, and doctors use this test to calculate glomerular filtration rate, or GFR, which dictates kidney function.
When kidneys are not able to filter the blood effectively, a build up of waste and excess fluid begins to occur in the body. Creatinine and blood urea nitrogen, or BUN, are two forms of waste that build up in the blood. When doctors check for kidney function, they need to examine how much of an abnormal presence of these wastes are in the body, the National Kidney Foundation states. Doctors also test the level of protein in urine when evaluating kidney health.
Doctors check for glomerular filtration rate, or GFR, in order to measure how well the kidneys are filtering the blood, MedlinePlus explains. They use a formula that accounts for a patient's age, body size, gender, ethnicity and creatinine level to calculate GFR.
Common symptoms of kidney problems include pain or blood during urination, the urge to frequently urinate, swollen hands or feet due to fluid backup, and the difficulty to start urinating, advises Healthline.