Also known as:CgA
Formal name:Chromogranin A
Related tests:Serotonin, 5-HIAA, Catecholamines, Tumor Markers
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Why Get Tested?
To help diagnose and monitor carcinoid tumors and other neuroendocrine tumors
When to Get Tested?
When you have symptoms suggestive of a carcinoid tumor, such as flushing, 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
Test Preparation Needed?
Fasting may be required; follow any instructions from your healthcare provider or laboratory
How is it used?
The chromogranin A (CgA) test is used as a tumor marker. It may be ordered in combination with a 5-HIAA test to help diagnose carcinoid tumors. It may also be used to detect the presence of other tumors arising from neuroendocrine cells.
Neuroendocrine cells are cells that have both nerve and hormone (endocrine) aspects and are found in organs throughout the body. These cells and the endocrine system 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, and neuroblastomas.
Many of these tumors release large quantities of hormones, such as serotonin, catecholamines, or insulin, continuously or intermittently, causing symptoms characteristic for that tumor. However, some neuroendocrine tumors do not release the expected hormones. In either case, neuroendocrine tumors are frequently associated with increased concentrations of CgA.
A CgA test may also be used to help monitor the effectiveness of treatment and detect recurrence of these tumors.
When is it ordered?
A CgA test is ordered along with other tests when a healthcare practitioner suspects that a person's signs and symptoms are due to a carcinoid tumor or other neuroendocrine tumor.
Some signs and symptoms may include:
- Flushing of the face and neck (appearance of deep red color, usually with sudden onset)
- Diarrhea, nausea, vomiting
- Rapid heart rate
- 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. A person with no signs or symptoms and a normal level of CgA is unlikely to have a neuroendocrine tumor. However, the test is not perfect, and it is possible to have a neuroendocrine tumor even if the concentration of CgA is normal.
An increased CgA level in a person with 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. The 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 concentration of CgA is proportional to the tumor burden - the mass of the tumor. If concentrations of CgA are elevated prior to treatment and then fall, then treatment is likely to have been effective. If monitored levels begin to rise, then the person may have a recurrence of the tumor.
Is there anything else I should know?
CgA concentrations may be elevated in conditions such as liver disease, inflammatory bowel disease, renal insufficiency, and with 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), which are drugs that reduce the amount of stomach acid.
There are currently no FDA-approved chromogranin A tests. Those CgA tests that have been developed and validated by laboratories are all slightly different, and their results are not interchangeable. When monitoring a patient over time, CgA tests should be performed by the same laboratory so that values can be compared.
What is being tested?
Chromogranin A (CgA) is a protein released from neuroendocrine cells. These are cells that secrete 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, and neuroblastomas. The CgA test may be used to help detect, diagnose, and/or monitor 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 the expected hormones. In either case, neuroendocrine tumors are frequently associated with increased concentrations of CgA.
Carcinoid tumors are slow-growing noncancerous or cancerous masses that form mainly in the gastrointestinal tract (especially in the appendix) and in the lungs. According to the American Cancer Society, there are about 8,000 gastrointestinal and 4,000 lung carcinoid tumors diagnosed each year in the United States. Many more of these tumors may exist, but most remain small and do not cause any symptoms. 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 sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation may be needed or fasting may be required. Follow any instructions from the healthcare provider or laboratory.
- Should everyone have a chromogranin A test?
No. This test is usually ordered to help diagnose and monitor a carcinoid or other neuroendocrine tumor, both of which are uncommon. Most people will never need to have this test performed.
- 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 under the microscope and makes a diagnosis. (For more on this, read the article on Anatomic Pathology.)
© 2017 American Association for Clinical Chemistry, republished from Lab Tests Online.*
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