Diagnosing Carcinoid Syndrome

Diagnosing carcinoid syndrome is often difficult, for two reasons. First, the disease is quite rare, affecting an average of only 2.5 to 4.5 out of every 100,000 Americans. As a result, many healthcare professionals see very few cases, even in a lifetime of practice. Second, the symptoms, especially in the early stages, are nonspecific and mimic those of other diseases, such as irritable bowel syndrome. As a consequence, misdiagnosis is common, and many patients see a succession of physicians and suffer for years before they receive an accurate diagnosis.¹ Accurate, early diagnosis is facilitated when healthcare providers are alert to the possibility of the syndrome and are aware of the steps needed to confirm it.

On this page, you'll find information to aid the process of diagnosis, including:

Detection of Carcinoid Syndrome Symptoms

The symptoms of carcinoid syndrome occur when carcinoid tumors secrete serotonin and other chemicals into the bloodstream.² These small, slow-groing tumors are usually found in the hormone-producing cells that line the small intestine or in other digestive tract cells, but they can be located in other parts of the body as well.³ Many of the symptoms of carcinoid syndrome seem unrelated, and each can be indicative of a range of other diseases. The most common signs and symptoms include the following⁴:

The clinical presentation of carcinoid syndrome can vary depending on the affected site (Table 1).

Key Diagnostic Tests

Further investigative testing should be carried out in any patient who is experiencing any of the symptoms of carcinoid syndrome. Two simple tests have relatively high accuracy for confirming or ruling out carcinoid syndrome⁴:

Urine 5-HIAA (5-hydroxyindoleacetic acid) test

The 5-HIAA test measures the amount of the serotonin metabolite 5-HIAA excreted in the urine in a 24-hour period. Serotonin is one of the key vasoactive substances secreted by carcinoid tumors, so measuring one of its metabolites can help to establish a diagnosis of carcinoid syndrome.⁴

To prevent false-positive results, the urine is collected after the patient has excluded serotonin-containing foods from his or her diet for 3 days. Such foods include⁴:

Certain drugs should also be discontinued temporarily before testing as well, including:

After 3 days of food and drug exclusion, a 24-hour urine sample is collected for assay. Values are as follows^4,7:

The 5-HIAA test is estimated to have a sensitivity of 73% and a specificity of 100% for carcinoid tumors.

To learn more about 5-HIAA and about how the 5-HIAA test is performed, click here.

Chromogranin A (CgA) test

The Chromogranin A (CgA) blood test measures CgA levels in carcinoid tumor cells. CgA is a glycoprotein that is stored in the secretory granules of these carcinoid tumor cells. Elevated CgA levels may indicate the presence of carcinoid tumors; such elevations are reported in 80% to 100% of patients with neuroendocrine tumors. ^{8, 9}

The CgA test does not distinguish between carcinoid tumors and other nonendocrine tumors or gastroenteropancreatic tumors. It is carried out on serum or plasma that is separated from cells. ^{8, 9}

Other Diagnostic Tests

When positive readings are obtained on biochemical testing, imaging tests are recommended to confirm the diagnosis. The optimal imaging method depends on the suspected site of the tumor and may include any of the following:

Somatostatin receptor scintigraphy (SRS) imaging can be used to locate the primary tumor and determine whether it has metastasized. SRS has the advantages of being both highly accurate and usable across all body systems. ^4,7

More information about biochemical monitoring in carcinoid syndrome is available here.

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