Diagnosing Carcinoid Syndrome
Doctors often have difficulty diagnosing carcinoid syndrome in its early stages. There are several reasons for this. Most of the symptoms are fairly common, and they're "nonspecific," meaning similar to symptoms that can be caused by many things. Flushing, for example, can be a menopausal symptom, a reaction to alcohol, or the side effect of a drug.
Adding to the challenge is the fact that carcinoid syndrome is a fairly rare condition. There's a chance that your physician was simply not looking for carcinoid syndrome when your symptoms first presented. That's why, if you've gotten to the point of getting your carcinoid syndrome diagnosed, you are more fortunate than many patients. You're well on your way toward taking control of carcinoid syndrome.
On this page, you'll learn:
How Your Condition will be Monitored
To maintain symptom control, you should be regularly monitored for changes in your symptoms or test results. Regular doctor visits will also help ensure that you get the best possible relief of symptoms.
There are several tests that your doctor can use to help keep on top of carcinoid syndrome. Separately, they all have advantages and disadvantages, but collectively they are your best bet for recognizing and monitoring carcinoid tumors and carcinoid syndrome.
The chromogranin A (CgA) blood test measures a protein found in tumor cells such as carcinoid. A urine test, 5-HIAA, measures a metabolite of serotonin, indicating the activity of carcinoid tumors. Your doctor may refer you to a radiologist for an imaging test — such as a computed tomography (CT) scan, magnetic resonance imaging (MRI), or OctreoScan®* — to see if they can detect the presence of a carcinoid tumor or tumors.
*OctreoScan® is a registered trademark of Mallinckrodt, Inc.
Chromogranin A (CgA) Testing
Chromogranin A (CgA) blood testing is considered to be the best test for detecting carcinoid tumors, and for monitoring their activity. Elevated levels of CgA are found in 80-100% of patients with carcinoid tumors.
A CgA test is fast, easy to perform, and accurate. However, a positive test result does not always indicate carcinoid tumors are present, because CgA levels can also be increased by neuroendocrine tumors. Therefore, further testing must be done to make a definitive diagnosis of carcinoid syndrome.
How the Test Is Done
A blood sample is taken and then tested with a CgA-specific enzyme-conjugated antibody. The antibody and enzyme bind the CgA protein as a "sandwich" — the purpose of the antibodies is to bind with the CgA protein, and the enzymes produce color. The intensity of the color is proportional to the specimen's CgA concentration. The CgA test uses CgA-specific antibodies to measure the level of CgA in the body.
Measurements may vary with meal consumption so patients are required to fast before a CgA test. CgA tests are performed every 3 to 6 months.
5-Hydroxyindole Acetic Acid (5-HIAA) Testing
5-HIAA testing is an easy, 24-hour test that is specific to carcinoid tumors - levels of 5-HIAA are not elevated with other types of tumors. This test is the most common biochemical test for carcinoid tumors.
Elevated levels of 5-HIAA, a by-product produced when serotonin breaks down in the body, can be detected from a urine sample. This test can positively detect carcinoid tumors 73% of the time, and is nearly 100% accurate, meaning that a positive result is rarely wrong. However, the level of 5-HIAA only becomes elevated when carcinoid tumors have metastasized to the liver, making the potential for a cure unrealistic. 5-HIAA testing is useful to estimate the extent of disease and survival.
Sometimes you can have what is called a false-positive test result. This happens when you eat foods rich in serotonin and your urine 5-HIAA levels go up. That is why your health care provider will probably advise you not to eat the following foods for 24 hours before you take the test:
- Bananas
- Walnuts
- Plantains
- Hickory nuts
- Pineapple
- Pecans
- Kiwi fruit
- Avocados
There are several drugs — for example, many that are contained in cough and cold medicines — that also affect the urine level of 5-HIAA. Your health care provider will probably tell you to avoid taking these drugs for 24 hours before you take the test:
- Acetaminophen (such as Tylenol®)*
- Salicylates (aspirin)
- Guaifenesin (found in some cough medicines)
- l-dopa (used to treat Parkinson's disease)
How the 5-HIAA Test Works
When serotonin breaks down in the body, it is converted first to 5-HT and then to 5-HIAA, which is excreted into the urine. A urine sample is collected, and the level of 5-HIAA in the urine is measured. By measuring the level of 5-HIAA in the urine, doctors are able to calculate the amount of serotonin in the body.
5-HIAA tests are performed every 3 to 6 months.
Somatostatin Receptor Scintigraphy (SRS) Testing
SRS testing is a commonly used imaging test used for detecting carcinoid tumors. The SRS test images all of the body's systems, and detects both tumors and metastases when somatostatin receptors are present (about 90% of tumors). The SRS test cannot detect tumors and metastases that do not express somatostatin receptors (about 10% of tumors). The advantage of SRS testing over conventional imaging such as a CT scan or MRI is the ability to image all body regions with high sensitivity and selectivity, allowing evaluation of tumors for therapy. Another advantage is that SRS testing can help show the density of somatostatin receptors.
How SRS Testing Works
The somatostatin analogue radiolabeled octreotide is administered intravenously, 4 hours before the imaging. The radiolabeled octreotide binds with somatostatin receptors and produces an image during the SRS test, which lasts 40 minutes. Twenty-four hours after the injection, the results of the scan are obtained.
Additional images are sometimes needed 48 hours after injection.
*OctreoScan® is a registered trademark of Mallinckrodt, Inc.
Why Is Early Diagnosis Important?
Carcinoid tumors are often difficult to diagnose because there are few if any symptoms. In fact, many carcinoid tumors are found through unrelated surgery or at autopsy. But, if metastasis occurs, patients may experience the uncomfortable and sometimes debilitating symptoms of carcinoid syndrome.
Unfortunately, the symptoms of carcinoid syndrome are often too vague for doctors to rule out other possible conditions, and they may misdiagnose the disease as something else, such as irritable bowel syndrome. Misdiagnosis then puts patients at a higher risk for carcinoid crisis — a life threatening complication of carcinoid syndrome.
Because of the difficulty involved, there may be a delay of anywhere between 2 and 20 years in correctly diagnosing carcinoid syndrome. This emphasizes the need for early recognition of the symptoms of carcinoid syndrome, and continued testing for the disease.
