Doctors use two tests to diagnose FAP: a colonoscopy and genetic testing. The care team may advise one or both of these tests when symptoms of FAP appear. If the child has a family history of FAP, these tests may happen before symptoms appear. After a diagnosis of FAP, the doctor may order more tests to find out how severe the disease is.
A colonoscopy involves using a thin, flexible tube (colonoscope) to look inside the colon. At the tip of the tube is a tiny video camera. The doctor uses the camera to look at the inside of the colon. If the doctor sees polyps during the colonoscopy, he or she will remove a small amount of tissue. The tissue will be tested in the lab, to see if there are any signs of cancer. This tissue is removed through the colonoscope, not with an open surgery.
Finding one to three polyps during a colonoscopy is most often not a concern. But if the care team finds more than three polyps, more tests will be done. A person who has more polyps may be diagnosed with FAP or some other polyposis syndrome.
The polyps may become cancerous about 10 years after the polyps appear. Finding FAP early is vital. It can help the care team make a personalized treatment plan before symptoms start. If a child has a family history of FAP, the doctor may advise having a colonoscopy between the ages of 10 and 12, and then do a repeat colonoscopy every one to two years.
Genetic Testing —
Genetic testing can confirm a diagnosis of FAP or variant forms of the disease. If a child has a family history of polyposis, the care team may advise that other family members have genetic testing for the disease as well.
Additional Testing —
Other tests can be done to help the care team find out how severe the child’s condition is. This can also help find polyps in hard-to-reach parts of the GI tract. The tests include:
Video capsule endoscopy — This involves swallowing a pill-sized, wireless camera that takes video inside the GI tract.
- Balloon-assisted enteroscopy — This helps check for and treat problems further into the small bowel. It can be used in place of surgery in some cases.
- Endoscopic retrograde cholangiopancreatography (ERCP) — This procedure uses X-ray and an endoscope. An endoscope is a thin, flexible tube with a strong light and tiny camera. The test helps doctors see the small ducts that drain the pancreas, liver, and gall bladder into the small intestine. In young adults and some children, it is vital to look for polyps in these parts as well.
For infants and young children with FAP, abdominal ultrasound and blood tests are used to screen for hepatoblastoma. This is a rare liver tumor linked to FAP.