The biomarkers below are tested as part of a Kidney Function Test - Learn how to understand your Kidney Function Test results and improve your numbers by registering for our free trial

Kidney function tests look for the level of waste products, such as creatinine and urea, in your blood to assess how well your kidneys are working and assess the health of your kidneys. As with liver function tests the combination of the tests are much more powerful that the individual tests in isolation and results for each marker are generally viewed in context of the overall test [51].


Creatinine is a chemical waste product that is produced by your muscle metabolism and to a smaller extent by eating meat. Healthy kidneys filter creatinine and other waste products from your blood. The filtered waste products leave your body in your urine.

If your kidneys aren’t functioning properly, an increased level of creatinine may accumulate in your blood. A serum creatinine test measures the level of creatinine in your blood and provides an estimate of how well your kidneys are filtering (glomerular filtration rate) [52].

Estimated Glomular Filtration Rate (eGFR)

Glomerular filtration rate (GFR) is a measure of the function of the kidneys. This test measures the level of creatinine in the blood and uses the result in a formula to calculate a number that reflects how well the kidneys are functioning, called the estimated GFR or eGFR.

The estimated glomerular filtration rate (eGFR) is used to screen for and detect early kidney damage, to help diagnose chronic kidney disease, and to monitor kidney status. It is a calculation based on the results of the blood creatinine test along with other variables such as age, sex, and race [54].

Blood urea nitrogen (BUN)

A Blood urea nitrogen (BUN) test reveals important information about how well your kidneys and liver are working. A BUN test measures the amount of urea nitrogen that’s in your blood.

Your body typically forms and gets rid of urea nitrogen as follows:

  • Your liver produces ammonia — which contains nitrogen — after it breaks down proteins used by your body’s cells.
  • The nitrogen combines with other elements, such as carbon, hydrogen and oxygen, to form urea, which is a chemical waste product.
  • The urea travels from your liver to your kidneys through your bloodstream.
  • Healthy kidneys filter urea and remove other waste products from your blood.
  • The filtered waste products leave your body through urine.

A BUN test can reveal whether your urea nitrogen levels are higher than normal, suggesting that your kidneys or liver may not be working properly [57].

BUN:Creatinine Ratio

The BUN:Creatinine ratio is the amount of Urea Nitrogen in the Blood divided by the amount of creatinine in the blood.

BUN and creatinine are the primary tests used to check how well the kidneys are able to filter waste products from your blood. The BUN-to-creatinine ratio generally provides more precise information about kidney function and its possible underlying cause compared with looking at creatinine or BUN in isolation [59].