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Diagnosing and Monitoring 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 are  "nonspecific," meaning similar to symptoms that can be caused by many things. Flushing, for example, can also be a menopausal symptom, a reaction to alcohol, or a side effect of a drug.

However, two symptoms that might suggest carcinoid syndrome rather than another condition include:

  • "Dry" flushing (flushing with no sweating), as opposed to "wet" flushing (flushing with sweating), which occurs as a symptom of menopause, for example
  • Nighttime diarrhea (or nocturnal diarrhea), as opposed to diarrhea during the day, which might be more likely to be caused by irritable bowel syndrome, for example

Adding to the challenge is the fact that carcinoid syndrome is a fairly rare condition. Your doctor might not have been looking for carcinoid syndrome when your symptoms first started. 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 helping to manage carcinoid syndrome.

There are several tests that your doctor can use to diagnose carcinoid syndrome and to monitor it once it has been diagnosed. It's important to be monitored regularly for changes in your symptoms or test results. Regular doctor visits will also help you get the best possible outcome.

On this page, you'll learn about:

*OctreoScan® is a registered trademark of Mallinckrodt, Inc.

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Chromogranin A (CgA) Testing

The Chromogranin A (CgA) blood test is a good marker to help detect and monitor the activity of carcinoid tumors in general. This includes carcinoid tumors that secrete certain hormones that are associated with carcinoid syndrome as well as carcinoid tumors that do not cause carcinoid syndrome. Elevated levels of CgA are found in 80-100% of patients with carcinoid tumors.

Chromogranin A(CgA) Testing
CgA is a protein found in carcinoid tumor cells, and it may be secreted into the blood. A blood sample is taken, and the level of CgA in the bloodstream is determined.

A CgA test is fast, easy to perform, and accurate. However, increased levels of this marker may also be caused by other factors such as renal failure, chronic atrophic gastritis or the use of proton-pump inhibitors.

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, while 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.

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5-Hydroxyindoleacetic Acid (5-HIAA) Testing

5-HIAA testing is a 24-hour urine 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 associated with carcinoid syndrome.

Elevated levels of 5-HIAA, a by-product produced when serotonin breaks down in the body, can be detected from a urine sample. Serotonin is one of the key body chemicals released by carcinoid tumors that are associated with carcinoid syndrome. The test can positively detect carcinoid tumors 73% of the time, and is generally regarded as an accurate test. However, the level of 5-HIAA only becomes elevated when carcinoid tumors have metastasized to the liver, making the potential for a cure less likely. 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
  • Plums
  • Tomatoes
  • Eggplant

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 may tell you to avoid taking these drugs for 24 hours before you take the test.

Consult with your physician about which medications are appropriate to take before this test.

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 Test

A tumor secretes 5-HT into to the bloodstream, where it is converted into 5-HIAA. A urine sample is taken, and the level of 5-HIAA in the bloodstream is determined.
5-HIAA tests are performed every 3 to 6 months.

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Somatostatin Receptor Scintigraphy (SRS) [OctreoScan®] 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 carcinoid tumors). The SRS test cannot detect tumors and metastases that do not express somatostatin receptors. 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 15-20 minutes. Twenty-four hours after the injection, the results of the scan are obtained.

Somatostatin Receptor Scintigraphy
Example of an SRS whole-body scan (OctreoScan®*) at 24 hours postinjection, revealing multiple carcinoid tumors in the liver, pelvis, abdomen, and brain.
Additional images are sometimes needed 48 hours after injection.

*OctreoScan® is a registered trademark of Mallinckrodt, Inc.

Imaging Tests

When positive readings are obtained on biochemical testing, imaging tests are recommended to confirm the diagnosis. Imaging methods your doctor may select depend on the suspected site of the tumor and may include any of the following:

  • Computed tomography (CT) scan
  • Magnetic resonance imaging (MRI)
  • Endoscopic ultrasonography

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Why Early Diagnosis of Carcinoid Syndrome Is 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 dangerous condition that can occur at the time of surgery, which can be a life threatening complication of carcinoid syndrome.

Because of the difficulty involved, there may be a delay of approximately 5-7 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.

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