Kidney Tests: GFR, Albumin, Creatinine, Imaging and Biopsy

You have two kidneys, each about the size of a fist, on either side of the backbone just above the waist. They filter and clean the blood, removing waste products and making urine. Kidney tests check how well they are working.

Who should be tested

Early kidney disease usually has no signs or symptoms, so testing is the only way to know. Get checked if you have any of the key risk factors:

• diabetes — get checked every year;
• high blood pressure;
• heart disease;
• a family history of kidney failure.

With the last three, ask your health care provider how often to be tested. The sooner kidney disease is found, the sooner treatment can help protect the kidneys.

The tests

Glomerular filtration rate (GFR)

One of the most common blood tests for chronic kidney disease, GFR shows how well the kidneys are filtering.

You cannot raise your GFR, but you can try to keep it from falling further.

Creatinine

Creatinine is a waste product from the normal breakdown of muscle, which the kidneys remove from the blood. Blood and urine tests check its level; the amount in the blood is used to estimate GFR, and it rises as kidney disease gets worse.

Albumin in the urine

Albumin is a protein in the blood. A healthy kidney does not let it into the urine; a damaged one lets some through. The less albumin in the urine, the better.

• Dipstick test. A strip of chemically treated paper dipped in a urine sample changes colour if albumin is present.
• Urine albumin-to-creatinine ratio (UACR). Compares albumin with creatinine in a urine sample, to estimate how much albumin would pass into the urine over 24 hours. A result of 30 mg/g or less is normal; more than 30 mg/g may be a sign of kidney disease.

A positive result may be repeated once or twice to confirm it.

Imaging

Tests such as ultrasound give pictures of the kidneys, so the provider can see their size and shape and check for anything unusual.

Kidney biopsy

A small piece of kidney tissue is taken and examined under a microscope, to find the cause of kidney disease and how much damage there is.

Keeping track

If you have kidney disease, the same GFR and albumin tests show whether treatment is working: a GFR that stays the same, and urine albumin that stays the same or falls, are good signs.

Sources

• MedlinePlus, U.S. National Library of Medicine, "Kidney Tests," drawing on the National Institute of Diabetes and Digestive and Kidney Diseases. https://medlineplus.gov/kidneytests.html
• National Institute of Diabetes and Digestive and Kidney Diseases, "Chronic Kidney Disease Tests & Diagnosis." https://www.niddk.nih.gov/health-information/kidney-disease/chronic-kidney-disease-ckd/tests-diagnosis
• Rewritten in hubnx's own words.