The Chromogranin A test may be used to help detect, diagnose, and/or monitor neuroendocrine tumors, especially carcinoid tumors.
Chromogranin A 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.
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.
The level of chromogranin A in the blood is normally low. A person with no signs or symptoms and a normal level of Chromogranin A 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 Chromogranin A 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 Chromogranin A is proportional to the tumor burden - the mass of the tumor. If concentrations of Chromogranin A 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.
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