Kidney Function Tests

What are kidney function tests?

Kidney function tests are used to assess the efficiency of kidneys in clearing waste from the body. These tests help assess kidneys’ overall health and functioning by evaluating their ability to filter waste products, maintain fluid and electrolyte balance, and regulate other essential bodily functions. By performing these tests, doctors can diagnose and monitor various kidney conditions and determine the appropriate treatment plan.

A kidney test may include a blood test, a 24-hour urine sample, or a combination of both. The test results are typically available on the same day or within a few days.

A laboratory technician will locate a vein in the arm, clean the site, and insert a small needle to draw blood into a vial. The process typically takes a few minutes. The blood sample will be sent to a lab for analysis.

What are the types of kidney function tests?

  • Serum Iron: This test measures the amount of iron in the blood. It helps determine if iron levels are within the normal range.
  • Total Iron-Binding Capacity (TIBC): The test measures the amount of transferrin, a protein responsible for transporting iron in the blood. This test provides information about the amount of free transferrin available to bind and carry iron throughout the body. When TIBC levels are elevated, more transferrin is free, suggesting lower iron levels in the blood.
  • Transferrin saturation: It measures the percentage of transferrin that is attached to iron.
  • Serum Ferritin: Ferritin is a protein that stores iron in the body. Measuring serum ferritin levels helps assess iron stores and detect iron deficiency or iron overload.

What are these tests used for?

Blood Tests

Serum Creatinine: A serum creatinine test measures the amount of creatinine, a waste product produced by muscle tissue breakdown, in your blood. This test helps determine how effectively kidneys remove creatinine from the bloodstream. A creatinine level higher than 1.2 mg/dL for women and 1.4 mg/dL for men indicates a kidney problem. For this test, a lower number is better. High creatinine levels can be a sign of acute kidney injury and chronic kidney disease.

Blood Urea Nitrogen (BUN) Test:  Urea nitrogen is a waste product found in the bloodstream, resulting from the breakdown of dietary protein. As you consume protein-rich foods, the body metabolizes them and produces urea nitrogen as a byproduct. The kidneys play a crucial role in filtering and removing urea nitrogen from the body as part of the waste elimination process. BUN (Blood Urea Nitrogen) levels can vary; typically, they tend to increase with age. The reference range for urea nitrogen typically falls between 7 and 20 mg/dL. Elevated BUN levels may indicate impaired kidney function; as kidney disease progresses, BUN levels tend to rise.

Estimated Glomerular Filtration Rate (eGFR) Calculation/Estimation:  It estimates how well kidneys are filtering waste products. GFR is calculated using equations considering factors such as creatinine levels, age, gender, and race.   A normal eGFR varies according to age and tends to decrease with age. In this test, a higher number is better. Typically, if your eGFR is lower than 60, it may indicate that the kidneys are not functioning properly. An eGFR lower than 15 is recognized as an indication of kidney failure.

Electrolyte Testing:  Assesses the levels of electrolytes (e.g., sodium, potassium, bicarbonate) in the blood. It helps evaluate the kidneys’ ability to maintain the appropriate balance of these substances.

Urine Test

Urinalysis: A urinalysis, or urine test, is a diagnostic procedure that involves analyzing various components of urine, including its physical properties, chemical composition, and microscopic elements. Urinalysis examines factors like urine colour, clarity, pH level, presence of proteins, glucose, ketones, blood, bilirubin, urobilinogen, nitrite, red and white blood cells, casts, and crystals.

A urinalysis is a valuable tool in diagnosing various conditions, such as urinary tract infections, kidney disease, and diabetes. It is often performed as part of routine check-ups when symptoms suggest urinary issues or as a follow-up to other medical investigations.

The urine albumin-creatinine ratio (uACR) test measures the levels of two substances in the urine: albumin (a protein) and creatinine. In a healthy kidney, albumin is retained in the blood while creatinine is filtered into the urine. Consequently, there should be minimal or no albumin present in the urine. The uACR is calculated by dividing the amount of urine albumin by the amount of urine creatinine, resulting in a ratio. A “normal” uACR level is typically below 30 mg/g. In this test, a lower uACR number is considered better. If the uACR level is 30 mg/g or higher, it may indicate albuminuria, which is the presence of elevated levels of albumin in the urine.

A 24-hour urine collection test is ordered to assess kidney stones, glomerular disease, or kidney function. It involves collecting all urine produced over a 24-hour period in a specialized container. This test is less common than others and is used when abnormal results are found in other tests or specific clinical situations.


  1. Cleveland Clinic. Kidney Function Tests. [Internet]. Cleveland Clinic; [updated 2021 Jan 21; cited 2023 Jun 23]. Available from: https://my.clevelandclinic.org/health/diagnostics/21659-kidney-function-tests
  2. Kidney Tests. [Internet]. National Library of Medicine; [updated 2022 May 2; cited 2023 Jun 23]. Available from: https://medlineplus.gov/kidneytests.html
  3. Centers for Disease Control and Prevention. Kidney Tests. [Internet]. U.S. Department of Health & Human Services; [updated 2021 Mar 2; cited 2023 Jun 23]. Available from: https://www.cdc.gov/kidneydisease/publications-resources/kidney-tests.html#:~:text=Urine%20albumin%2Dto%2Dcreatinine%20ratio%20(UACR).&text=A%20UACR%20test%20lets%20the,twice%20to%20confirm%20the%20results.
  4. National Kidney Foundation. Tests to check your kidney health. Available from: https://www.kidney.org/atoz/content/tests-to-check-your-kidney-health

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