The doctor will ask about your symptoms and medical history, and perform a physical exam. Tests may include:

Commonly Ordered Blood Tests—including complete blood count; calcium, phosphorus, and parathyroid hormone; and potassium levels

Blood Urea Nitrogen (BUN) and Creatinine—to see whether your kidneys are working properly. If they 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.

Estimated Glomerular Filtration Rate—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.

The formula used in clinical practice is called the Cockcroft-Gault equation:

Creatinine clearance or GFR (mL per minute) = (140 – age) X body weight in kilogram ÷ 72 X serum creatinine. If calculated for a female, this product is multiplied by 0.85. The GFR determines the stage of chronic renal disease.

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)

Blood Electrolytes—The concentration of sodium, chloride, calcium, and potassium in the blood will be abnormal. Potassium, in particular, can quickly rise to dangerous levels.

Urine Tests—to see if the kidneys are working properly. If they are not working properly, your urine will contain protein. You may be asked to collect urine in a special container over a 24-hour period. This test will also show whether your kidneys are clearing creatinine at a normal rate. 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,]]>]]>magnetic resonance imaging (MRI),]]> or ]]>computed tomography (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.

Kidney Biopsy—A small piece of kidney may be surgically removed and sent to a laboratory in order to try to ascertain the cause of kidney failure.