Most individuals with non-functioning carcinoid tumours (ones that aren't secreting) go for many years with no symptoms. It's usually only when abdominal pain and a change in bowel habits occur that they see their doctor. Once these symptoms are investigated, the doctor can determine the cause.
Carcinoid syndrome can be easily diagnosed when all of its features, or even one or two of its main symptoms, are present. However, because the syndrome is rare, even when there are many symptoms, it may be overlooked.
If carcinoid syndrome is suspected, the diagnosis usually can be confirmed quickly and painlessly by doing a urine test for 5-HIAA (5-hydroxyindole acetic acid - the waste product of serotonin). By measuring the amount of 5-HIAA in the urine over a 24-hour period, your doctor can tell how much serotonin is produced during that time. In carcinoid syndrome, the amount of 5-HIAA is almost always above normal.
This test is very good at identifying active disease; however, it may miss non-secreting carcinoid tumours or it may give false-positive results since some foods and medications can also cause high 5-HIAA levels in the urine.
Preparation for the 5-HIAA test requires avoiding certain foods and medications for a day or two before the test, as they may cause inaccurate test results. These include:
- pineapple (and its juice)
- red plums
- kiwi fruit
- various cough medications
- muscle relaxants
- iodine solutions
- MAO inhibitors
- phenothiazines (prochlorperazine,
Sometimes the 5-HIAA in the urine won't be higher than normal, but other carcinoid markers in the blood, such as chromogranin A and serotonin, will be. The tryptophan level in the blood is usually lower than normal.
Standard X-ray and imaging tests are then used to find the location of the tumour and identify how far it has spread. These tests may include a routine chest X-ray, CT or MRI scan, barium enema, and upper GI (gastrointestinal) and small bowel X-ray studies. Occasionally, it is also helpful to have an upper and lower GI tract endoscopy, which is a procedure that uses a flexible fibre optic tube to look inside the GI. However, these tests do not detect all carcinoid cases.
Another useful though expensive method of finding about 85% of carcinoid tumours is an OctreoScan. This involves injecting a tiny dose of a radioactive isotope that's specifically attracted to, and concentrated in, carcinoid tumour tissue. Carcinoid tumours then light up when a radiation scan is taken over the entire body, thus pinpointing the tumour location. The harmless radioactive isotope is excreted by the body in a few days.
An OctreoScan can be very helpful in confirming the diagnosis and locating the tumour in the rare cases of carcinoid syndrome, where all the symptoms and chemical findings are known but tests to locate the tumour turn up negative.