The doctor will ask about your symptoms and medical history. A physical exam will be done. Tests may include:

Blood urea nitrogen (BUN) and creatinine—If the kidneys are not filtering the blood properly, the blood will contain excess amounts of creatinine and urea. Creatinine is a byproduct of muscle function, while urea is a waste product of protein metabolism.

Other tests to check blood component levels—These may include a complete blood count and a check on calcium, phosphorus, parathyroid hormone, blood electrolytes, and potassium levels.

Estimated glomerular filtration rate (GFR) —A measurement of how well the kidneys are processing wastes. Your doctor can calculate the GFR based on gender, age, body size, and blood creatinine level.

StageGlomerular Filtration Rate (GFR)
1over 90 mL/min (normal)
260-89 mL/min (mild decrease)
330-59 mL/min (moderate decrease)
415-29 mL/min (severe decrease)
5under 15 mL/min (kidney failure or end-stage renal disease)

Urine tests—You may be asked to collect urine in a special container over a 24-hour period. This test will also show how well your kidneys are clearing creatinine. The amount of urine you produce is also significant. If your kidneys are failing—or starting to fail—you may produce little or no urine.

Renal imaging—The use of ultrasound, MRI scan, or CT scan to take pictures of the kidneys. These pictures will show whether urine flow is blocked or whether there is a change in the size of the kidneys. Some may use contrast dyes to highlight the structures.

Kidney biopsy—Tissue from the kidney is removed and examined under a microscope for abnormalities.