What is a kidney biopsy?
The word biopsy comes from the Greek words bios (life) and opsis (vision) and it involves the examination of tissues removed from a living organism. A kidney (or renal) biopsy is where a small piece of tissue is taken from the kidney to be examined under a microscope.
Why is kidney biopsy performed?
It is performed when there are symptoms and signs of kidney disease, but it is impossible to make a precise diagnosis with the help of blood tests, X-rays or other investigations.
The usual reasons for doing a renal biopsy are
- large amounts of blood and protein in the urine, with impaired kidney function,
- when it is uncertain whether a mass (tumour) in the kidney is cancer or not, and
- to determine if there is rejection of the kidney after renal transplantation.
How is a kidney biopsy performed?
There are four techniques for renal biopsy:
- percutaneous needle
- open surgical
- laparoscopic, and
- transjugular biopsy.
The word percutaneous means “through the skin”. Percutaneous needle biopsy is usually performed with the patient awake, while the skin over the kidney is injected with a painkiller (local anesthesia, usually lignocaine). The patient normally lies on his stomach, but in the case of a transplanted kidney he lies on his back. The kidney is visualized with ultrasound (sonar) or X-ray imaging (computerized tomography – CT) and a biopsy needle 1-2 mm in diameter is passed through the skin into the kidney. The needle has a hollow section inside, and triggering the needle takes a core of tissue 1-2 mm in diameter and 8-10 mm in length.
Open renal biopsy is performed with the patient asleep (under general anaesthesia) and lying on the side opposite to the kidney that is biopsied. A cut about 10-15 cm long is made in the flank, and under direct vision a small sliver of tissue about 10 by 5 mm is cut out of the kidney. Bleeding is stopped by placing stitches into the kidney, sometimes also using a special type of gauze or glue that promotes blood clotting.
Laparoscopy is done under general anaesthesia. Two small cuts 5-10 mm in diameter are made in the flank. Through one of these cuts a tubular telescope with a camera is inserted to directly visualize the kidney, and through the other an instrument (biopsy forceps) is passed. Small pieces of kidney tissue are taken with the forceps, and bleeding is stopped by burning with a laser.
Transjugular biopsy is where a thin catheter is inserted into the jugular vein in the neck. The catheter is passed down into the renal vein and a biopsy needle is passed through the catheter to obtain tissue cores from the inside of the kidney.
A specially trained doctor (a pathologist) examines the kidney tissues under a microscope and makes a diagnosis based on the appearance of the cells (histology).
How should I prepare?
The doctor should explain the whole procedure to you, including the risks and possible problems (complications), and you should be given an informed consent form to sign. You should tell the doctor if you are taking any medicines because some of them may impair the ability of your blood to clot. The doctor will usually do a blood test to determine if you have any blood clotting disorder.
You should not eat or drink anything for about 6 hours before the procedure. If it is done under local anaesthesia, there will be some pain where the local anaesthetic is injected into the skin, but you will usually not feel pain when the biopsy needle is put into the kidney itself. The doctor will ask you to take a deep breath and hold your breath, so that the kidney does not move when the needle is placed into it. This usually takes 10-30 seconds, during which time you should not exhale. The doctor may take several biopsy cores, each time asking you to hold your breath. You will usually be kept in hospital for some time after the procedure to see if there are any complications.
What are the risks?
The main risk is bleeding from the kidney, which has a very rich blood supply. The blood may accumulate around the kidney and not be recognized until a litre or more has been lost, so it is important to have your pulse and blood pressure regularly checked for 24-48 hours after the procedure. The blood may also go down the kidney tube (ureter) to the bladder, so you may see blood in your urine. If the bleeding is severe, blood transfusion may be necessary. If the bleeding continues, it may be necessary to get special X-rays (arteriogram) to see which blood vessel in the kidney is bleeding, so that it can be plugged (embolized) with material injected into the vessel.
Sometimes it is necessary to do an open operation, and in rare cases it may be necessary to remove the kidney to stop the bleeding. Infection may occur as a result of the biopsy, but this is rare. Symptoms that indicate a possible complication after kidney biopsy include bloody urine more than 24-48 hours after the procedure, inability to pass urine, increasing pain at the biopsy site, fever, dizziness or fainting.
What are the limitations of the procedure?
The pieces of tissue may be too small to make a definitive diagnosis under the microscope, or the biopsies may not be representative, with the result that the wrong diagnosis is made. In about 90% of cases, however, the correct diagnosis can be made and the risk of complications is comparatively small (about 5%).