What Is a Kidney Function Test?

A kidney function test allows a physician to measure how well a person's kidneys are working to remove wastes from the body, according to the National Kidney Foundation. Kidney function tests are done by collecting blood and urine, or, in some cases, with an imaging machine or with a biopsy.

An important blood test that shows what level the kidneys are functioning at is the BUN test, according to the National Kidney Foundation. When testing shows a high BUN level, it normally indicates that the kidneys are not working properly, according to Mayo Clinic. Serum creatinine testing is also a blood test used to measure creatinine levels in the blood. A rise of over 1.2 for women and 1.4 for men often signals that there is a problem with the kidneys, according to the National Kidney Foundation.

With urinalysis, a chemically treated strip is used to test for anomalies such as excess pus, blood, protein, sugar and bacteria in the blood, as excess amounts of these substances cause the strip to change colors, according to the National Kidney Foundation. Microalbuminuria tests look for a protein called albumin inside the urine, which can indicate kidney malfunction. Creatinine clearance tests are used to compare the creatinine in a sample of urine to a blood test to show the blood filtered out by the kidneys.