Tests to Measure Kidney Function, Damage and Detect Abnormalities


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Healthy kidneys remove wastes and excess fluid from the blood. Blood and urine tests show how well the kidneys are doing their job. Urine tests can show how quickly body wastes are being removed and whether the kidneys are leaking abnormal amounts of protein. Here's a quick guide to the tests used to measure kidney function.

Blood Tests

Serum Creatinine Creatinine (kree-AT-uh-nin) is a waste product that comes from the normal wear and tear on muscles of the body. Creatinine levels in the blood can vary depending on age, race and body size. A creatinine level of greater than 1.2 for women and greater than 1.4 for men may be an early sign that the kidneys are not working properly. The level of creatinine in the blood rises, if kidney disease progresses.
Glomerular Filtration Rate(GFR) This test is a measure of how well the kidneys are removing wastes and excess fluid from the blood. It may be calculated from the serum creatinine level using your age, weight, gender and body size. Normal GFR can vary according to age (as you get older it can decrease). The normal value for GFR is 90 or above. A GFR below 60 is a sign that the kidneys are not working properly. A GFR below 15 indicates that a treatment for kidney failure, such as dialysis or a kidney transplant, will be needed.
Blood Urea Nitrogen (BUN) Urea nitrogen (yoo-REE-uh NY-truh-jen) comes from the breakdown of protein in the foods you eat. A normal BUN level is between 7 and 20. As kidney function decreases, the BUN level rises.

Imaging Tests

Ultrasound This test uses sound waves to get a picture of the kidney. It may be used to look for abnormalities in size or position of the kidneys or for obstructions such as stones or tumors.
CT Scan This imaging technique uses contrast dye to picture the kidneys. It may also be used to look for structural abnormalities and the presence of obstructions.

Kidney Biopsy

A biopsy may be done occasionally for one of the following reasons:
  • to identify a specific disease process and determine whether it will respond to treatment
  • to evaluate the amount of damage that has occurred in the kidney
  • to find out why a kidney transplant may not be doing well

A kidney biopsy is performed by using a thin needle with a sharp cutting edge to slice small pieces of kidney tissue for examination under a microscope.

Urine Tests

Some urine tests require only a couple of tablespoonfuls of urine. But some tests require collection of all urine produced for a full 24 hours. A 24-hour urine test shows how much urine your kidneys produce in one day. The test also can give an accurate measurement of how much protein leaks from the kidney into the urine in one day.
Urinalysis Includes microscopic examination of a urine sample as well as a dipstick test. The dipstick is a chemically treated strip, which is dipped into a urine sample. The strip changes color in the presence of abnormalities such as an excess amount of protein, blood, pus, bacteria and sugar. A urinalysis can help to detect a variety of kidney and urinary tract disorders, including chronic kidney disease, diabetes, bladder infections and kidney stones.
Urine Protein This may be done as part of a urinalysis or by a separate dipstick test. An excess amount of protein in the urine, called proteinuria (pro-TEEN-yu-ree-uh). A positive dipstick test (1+ or greater) should be confirmed using a more specific dipstick test (an albumin specific dipstick) or by a quantitative measurement, such as albumin-to-creatinine ratio.
Microalbuminuria This is a more sensitive dipstick test, which can detect a tiny amount of protein called albumin in the urine. People who have an increased risk of developing kidney disease, such as those with diabetes or high blood pressure, should have this test if their standard dipstick test for proteinuria is negative.
Creatinine Clearance A creatinine clearance test compares the creatinine in a 24-hour sample of urine to the creatinine level in your blood to show how much blood the kidneys are filtering out each minute.

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©2014 National Kidney Foundation. All rights reserved. This material does not constitute medical advice. It is intended for informational purposes only. Please consult a physician for specific treatment recommendations.