When you have symptoms suggestive of a carcinoid tumor, such as flushing, abdominal pain or discomfort followed by diarrhea, and/or wheezing; when your healthcare provider thinks that you may have a carcinoid or other neuroendocrine tumor
A blood sample drawn from a vein in your arm
Fasting may be required; stopping certain medications may be necessary. Follow any instructions from your healthcare provider or laboratory. However, do not stop taking your medication(s) unless instructed to do so by your healthcare practitioner.
Chromogranin A (CgA) is a protein released from neuroendocrine cells. These are cells that release hormones in response to signals from the nervous system. They are found in organs throughout the body. This test measures the amount of chromogranin A in the blood.
Neuroendocrine cells, and the endocrine glands that they are found in, can give rise to a variety of tumors, both benign and malignant. Examples include carcinoid tumors, insulinomas, small cell lung cancers, pheochromocytomas, medullary thyroid carcinomas, some pituitary tumors, and neuroblastomas. The CgA test may be used to aid in detection, diagnosis, or monitoring response to treatment or relapse of neuroendocrine tumors, especially carcinoid tumors.
Many of these tumors release large quantities of the hormone associated with that tissue, either continuously or intermittently, causing symptoms characteristic for that tumor. However, not all neuroendocrine tumors release expected hormones. In either case, neuroendocrine tumors are frequently associated with increased concentrations of CgA.
Carcinoid tumors, a subset of neuroendocrine tumors, are slow-growing noncancerous or cancerous masses. These form mainly in the digestive tract (stomach, pancreas, small intestine, colon, appendix, rectum) or the lungs. According to the American Cancer Society, there are about 8,000 gastrointestinal carcinoid tumors and 2,000 to 4,500 lung carcinoid tumors newly diagnosed each year in the United States.
When carcinoid tumors are discovered in asymptomatic patients during surgical procedures performed for other reasons, they are called "incidental" tumors. A small percentage of these tumors may eventually grow large enough to cause obstructions in the intestines or bronchial tubes of the lungs.
How is the test used?
The chromogranin A (CgA) test is used as a tumor marker. It may be ordered alone or in combination with a 5-HIAA test to help diagnose carcinoid tumors. CgA may also be used to detect the presence of other tumors arising from neuroendocrine cells.
A CgA test may also be used to help monitor the effectiveness of treatment and detect recurrence of these tumors.
When is it ordered?
Some signs and symptoms may include:
- Flushing of the face and neck (appearance of deep red color, usually with sudden onset)
- Diarrhea, nausea, vomiting, abdominal pain, and signs of intestinal blockage
- Rapid heart rate
- Chest pain, wheezing, coughing, difficulty breathing
This test may be ordered periodically to help evaluate treatment effectiveness and monitor for tumor recurrence.
What does the test result mean?
The level of chromogranin A in the blood is normally low. If you have no signs or symptoms and a normal level of CgA, it is unlikely you have a neuroendocrine tumor. However, no test is one hundred percent accurate, and it is possible to have a neuroendocrine tumor, even if the level of CgA is normal.
An increased CgA level when you have symptoms may indicate the presence of a tumor, but it is not specific for the type of tumor or its location. In order to diagnose the condition, the tumor itself must be located, biopsied, and examined by a pathologist. Your healthcare practitioner will frequently follow an abnormal test result with an order for an imaging scan to help locate any tumor(s) that may be present.
Not all patients with a neuroendocrine tumor have typical signs and symptoms. Some tumors do not produce the hormone associated with that tissue or only produce it intermittently.
The level of CgA is proportional to the tumor burden (the mass of the tumor). If levels of CgA are elevated prior to treatment and then fall after treatment is started, then treatment is likely to have been effective. If following the treatment, the monitored levels begin to rise; then you may have a recurrence of the tumor.
Besides a neuroendocrine tumor, what else can cause elevated CgA levels?
CgA levels may be elevated in conditions such as liver disease, inflammatory bowel disease, pancreatitis, chronic bronchitis, renal insufficiency, and stress. These possible causes for elevated CgA levels should be considered when interpreting test results.
Chromogranin A can also be increased in people who take proton pump inhibitors (PPIs) or histamine 2 receptor antagonists, which are drugs that reduce the amount of stomach acid. Other medications that could alter the CgA level are serotonin reuptake inhibitors, which are used for the treatment of depression. It is sometimes recommended to avoid these medications to obtain reliable CgA results. Follow the instructions from your healthcare provider or laboratory and do not stop taking your medications unless instructed by your healthcare practitioner.
How does a healthcare practitioner locate the carcinoid or neuroendocrine tumor?
This is usually accomplished through the use of imaging scans such as x-rays, computed tomography (CT), or magnetic resonance imaging (MRI). In some cases, surgery is required to find the tumor. For more on these imaging tests, visit RadiologyInfo.org.
How does the healthcare practitioner tell whether a tumor is benign or cancerous?
In order to determine whether the tumor is benign or cancerous, the healthcare practitioner will need to perform a biopsy or remove the tumor surgically. The tumor is sent to the laboratory, where a pathologist examines the tumor cells using a microscope and makes a diagnosis. (For more on this, read the article on Anatomic Pathology.)
Is there anything else I should know?
There is currently no FDA-approved chromogranin A test, and FDA approval for this test is not required. Those CgA tests that have been developed and validated by individual laboratories are all slightly different, and their results are not interchangeable. When monitoring CgA levels over time, the tests should be performed by the same laboratory and the same method so that values can be compared.