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The Test Sample
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.