Creatinine clearance
Creatinine clearance measures how much creatinine is in your urine compared to how much there is in your blood. It is the most accurate measure of how well the kidneys are cleaning the creatinine out of your body. Creatinine clearance is determined by a 24-hour urine collection test and by a blood test.

CAT scan
A CAT scan is a type of X-ray. The patient lies inside a machine while a CAT scan is being made. The CT machine uses X-rays to build an image of the section or "slice" of the patient's body. Radiopaque fluid, which helps make the organs visible to X rays, is not always required for a CAT scan.

Kidney biopsy
A hollow needle is used to remove a very small piece of the kidney. This piece is studied under a microscope. The results of a kidney biopsy can be used to determine the cause of kidney failure. A biopsy is also used to check whether a transplanted kidney is being rejected.

Before a biopsy, local anesthetic is used to numb the area where the needle will be inserted. After a biopsy, the patient will need to rest for a few hours, but it may be possible to go home the same day.

MRI scan
MRI stands for Magnetic Resonance Imaging, a scanning technique that uses magnetism, radio waves and a computer to produce high-quality pictures of the inside of the body. The patient lies inside a large machine that sends signals to a computer that builds an image of the inside of the body. No X-rays are required.

This technique may provide a good image of the inside of the kidney and help doctors identify cause of your kidney failure.

Renal angiogram
For this test, a plastic tube is fed up an artery from the groin toward the kidney. A special dye that shows up on X-rays is injected into the tube. This makes it possible to take pictures of the blood vessels of the kidney, allowing doctors to see blockages.

A renal angiogram is a complex procedure. Possible side effects include bruising in the groin and pain, or damage to the kidneys by toxic dye. The risk of making the kidney function worse is as high as 10% in some patients, such as those with diabetes. Complications following a renal angiogram can, in 1 of 1,000 cases, be fatal.

Ultrasound scan
This is commonly used on pregnant women to check on the baby in the uterus. It is also used to help find the cause of kidney problems, either when kidney failure is first discovered, or if there appear to be problems after a transplant.

To perform an ultrasound scan a special jelly is spread on the skin and an ultrasound probe moved over the abdomen and sides. This allows the kidneys to be seen on the screen. The person carrying out the test may print photographs of certain images seen on the screen.

The test is quick and painless for the patient and tells the doctor if a kidney is too big, too small, or even missing. Ultrasound scans may be used so the doctor can locate the kidney before doing a biopsy.

X-ray
Various types of X-ray are used to investigate kidney problems. These special tests require the use of radio-opaque fluid. This fluid shows up well on X-ray film. It may be injected into the bloodstream or flushed into the area to be X-rayed using a fine tube called a catheter. X-ray exams of the kidney, bladder or blood vessels include:

Exposure to X-rays is potentially dangerous for unborn children. If you are pregnant, or suspect you may be, you should tell your doctor.