Site-specific biopsies and cell sampling are also used in the evaluation of people with suspected kidney and urinary tract disorders. (See also Overview of the Urinary Tract.)
A kidney biopsy (in which a sample of kidney tissue is removed and examined under a microscope) is primarily used to help the doctor diagnose disorders that affect the specialized blood vessels of the kidney (glomeruli) and tubules and unusual causes of acute kidney injury. A biopsy is often done on a transplanted kidney to look for signs of rejection.
When undergoing a kidney biopsy, the person lies face down, and a local anesthetic is injected into the skin and muscles of the back over the kidney. Ultrasonography or computed tomography (CT) is used to locate the part of the kidney where the glomeruli are located and to avoid large blood vessels. The biopsy needle is inserted through the skin and into the kidney.
This procedure is usually not done in people with uncontrolled high blood pressure, bleeding disorders, active urinary tract infections, or only one kidney (except for a transplanted kidney). Complications include bleeding into the urine around the kidney and formation of small arteriovenous fistulas (abnormal connections between very small arteries and veins) within the kidney.
Bladder biopsy is done most commonly to diagnose bladder cancer. Bladder biopsy is also sometimes done to diagnose other disorders, including interstitial cystitis and, rarely, to diagnose infections such as schistosomiasis that are rare in the developed world. Sometimes doctors use bladder biopsies to assess a person's response to treatment (called surveillance). Bladder biopsy is usually not done or is done only when using special precautions in people who have bleeding disorders (such as hemophilia). If a person has a urinary tract infection, bladder biopsy usually is not done until after the infection has been treated.
Biopsies can be done in a doctor's office using local anesthesia or in an operating room using general anesthesia. If a large amount of tissue is removed or if there is a risk of bleeding after the procedure, a drainage tube (catheter) may be left in the bladder to drain blood and clots and keep them from blocking the urethra.
Prostate biopsy is the only definitive way to diagnose prostate cancer (for example, if a man has a high level of prostate-specific antigen measured or if a doctor feels a nodule when doing a rectal examination). Complications of prostate biopsy are rare. They include excessive bleeding from the rectum and bodywide infection. Thus, prostate biopsy is usually not done if the man has a bleeding disorder or urinary tract infection. Before the procedure, men should stop taking drugs that impair blood clotting (including aspirin).
Some doctors prescribe oral or injected antibiotics around the time of the biopsy, and some doctors recommend an enema before the biopsy. Doctors insert an ultrasound probe into the rectum to provide images of the prostate to help guide placement of the biopsy needle. Doctors usually give the man a local anesthetic or sedation, and then they insert a needle through the ultrasonography probe or through the perineum into the prostate and remove many samples of tissue. The tissue is then examined in the laboratory to look for signs of cancer. A modification of the prostate biopsy is an MRI fusion biopsy. A man has an MRI scan of the prostate and then 1 to 2 weeks later has an ultrasound-guided prostate biopsy. During the biopsy exam, the pictures from the MRI and the ultrasound image are digitally combined (fused) to help create a more accurate image of abnormal areas for biopsy.
Urine cytology (microscopic examination of the urine to look for cancer cells) is sometimes useful in diagnosing cancers of the kidneys and urinary tract. For people at high risk—for example, smokers, petrochemical workers, and people with painless bleeding—urine cytology may be used to screen for cancer. For people who have had a bladder or kidney tumor removed, the technique may be used for follow-up evaluation. However, the results can sometimes indicate cancer when none is present, or they can fail to indicate cancer when it is present, especially if the cancer is very new or growing slowly.