What is the test?
A kidney biopsy is a procedure to obtain a sample of your kidney tissue so that it can be examined under a microscope. A kidney biopsy is useful in patients with kidneys that are not functioning properly, to determine the cause of the problem and the most appropriate treatment.
How do I prepare for the test?
You will need to sign a consent form giving your doctor permission to perform this test. Tell your doctor if you have ever had an allergic reaction to lidocaine or the numbing medicine used at the dentist's office.
Your doctor will order blood tests to find out if you are at extra risk for bleeding after the procedure. If you take aspirin, nonsteroidal anti-inflammatory drugs, vitamin E or other medicines that affect blood clotting, talk with your doctor. It may be necessary to stop or adjust the dose of these medicines before your test. If you have diabetes and take insulin, discuss this with your doctor before the test.
You will be told not to eat or drink anything after midnight the night before the test. This is a safety precaution in case you are one of the rare patients who has a complication that might require surgery on the same day as the procedure. You should continue to take your medicines with sips of water even though you are not eating a meal, however. This is particularly important for blood pressure medicines-if your blood pressure is too high on the day of the test, your doctor will probably not do the procedure.
You should plan on spending one night in the hospital after this test so that you can be monitored for complications such as bleeding.
What happens when the test is performed?
On the day of the test, you provide a urine sample to be tested for signs of a bladder infection. If you have an infection in the urine, you need to get treatment before you are able to have the biopsy done. Your blood pressure is measured. You will have an IV (intravenous) line placed in a vein in case you need any fluid during the procedure.
You lie on your stomach with a pillow under your abdomen to support you. You then have an ultrasound, a painless test that uses sound waves to create a picture of the internal organs. Some clear jelly is squirted onto your back on both sides; then the ultrasound sensor, which resembles a microphone, is held against your back. The doctor uses the ultrasound to make sure you have two kidneys (occasionally, a person is born with just one kidney) and to locate the one that is to have a sample taken. You are asked to take a deep breath, a shallow breath, and a normal breath and to hold each one. This allows the doctor to see what type of breathing moves the kidney into a position where it is easy to biopsy.
Some numbing medicine is injected under your skin and into the muscle that the biopsy needle is to go through. The ultrasound sensor continues to show the kidney while this medicine is being injected. You will feel some brief stinging from the numbing medicine.
A special sampling needle is then pushed gently into the area that has been numbed by the medicine. The doctor pushes this needle forward until it is just at the edge of the kidney. Your doctor then releases a special spring-loaded mechanism on the needle that quickly moves the needle a short distance into and out of the kidney to collect the sample. Some patients feel some discomfort from each biopsy, but because the needle moves so quickly, this lasts only for a second. Your doctor asks you to hold a large or small breath (as you practiced earlier) when the kidney is being sampled. The needle is removed and the sample put aside for testing. A second sample is taken from the same kidney using the same technique.
A bandage is placed on your back where the needle was inserted. The doctor takes another look with the ultrasound to see that you do not have any bleeding around your kidney.
What risks are there from the test?
The most serious risk from this test is bleeding. Many patients have a small amount of bleeding into the space around the kidney, but in a few patients this can be significant enough to require a transfusion and, in rare cases, even surgery. Somewhere between 1 and 3 patients out of every 1,000 have serious bleeding that requires a transfusion.
Almost all patients have some bleeding into their urine that can be seen with urine tests under the microscope. About 1% of patients have enough bleeding into the urine that the color of urine changes from yellow to a red color. The bleeding into the urine is almost always temporary.
It is possible, but unlikely, that you will develop a kidney infection after this test. Most patients have a small amount of soreness in their back for a day or two where the needle was placed.
Must I do anything special after the test is over?
You will probably spend the night in the hospital so that you can have a blood test done to check for bleeding, and so that your urine can be checked to make sure any blood in the urine is clearing up. You will be asked not to walk around for three hours after your biopsy.
How long is it before the result of the test is known?
Your kidney samples must be treated with special stains and treatments before they can be viewed under the microscope and under a special high-power electron microscope. The report of your results may require a full week or more.