To diagnose kidney failure, blood tests are generally used to measure the buildup of waste products in the blood. The two major blood chemical levels that are measured are the “creatinine level” and the “blood urea nitrogen” (BUN) level. With kidney failure, BUN and creatinine become elevated, and the glomerular filtration rate decreases. The glomerular filtration rate is the rate with which blood is filtered through the kidneys and can be calculated based upon the creatinine level, age, race, and gender of the patient.

Doctors use a urine test, the “creatinine clearance,” to measure the level of kidney function. The patient saves urine in a special container for one full day. The waste products in the urine and in the blood are estimated by measuring the creatinine. By comparing the blood and urine level of this substance, the doctor has an accurate idea of how well the kidneys are working. This result is called the creatinine clearance.

Urine tests may also be used to measure the amount of protein, to detect the presence of abnormal cells, or to measure the concentration of electrolytes. Abdominal ultrasound can also be used to assess the size of the kidneys and to help identify whether any obstruction exists. A biopsy of the kidney may also be done to get bits of kidney tissue to examine under the microscope.

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