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Chromogranin A (CgA) is the common name for the protein called parathyroid secretory protein 1. It belongs to the family of proteins that are secreted by cells within the nervous and endocrine system. It was first discovered in the cells of the adrenal medulla, and this gland is where most of CgA is produced. Other types of organs that will produce Chromogranin A are mainly cells within the pancreas and thyroid glands. CgA is peptide that is used to make various neuroendocrine hormones. These include hormones such as vasostatin and parastatin, which mainly work in neuron transmission. It is also released when other secretory cells make and release calcitonin or catecholamines. However, the exact function of Chromogranin A is not known. Since it is a precursor for various hormones, it can be detected in the blood of patients with an endocrine or neuroendocrine tumor. The laboratory test for chromogranin A is also used to detect if the patient is out of remission, and the cancer has returned. CgA peptide is increased in the blood in the presence of pheochromocytomas, and endocrinologists have used it as a marker for the presence of prostate cancer. Since it is produced by the pancreas, it also been shown to be elevated in patients with diabetes.
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Symptoms Of Elevated CgA
An elevation of CgA in the blood will not produce any symptoms associated with it, but rather any symptoms the person has will be as a result of the organ in which the tumor is located. CgA is usually in low levels in the blood, but will increase in the presence of cancers in the specific organs previously mentioned. For example, a carcinoid tumor will produce symptoms of flushing in the face, abdominal pain and cramping potentially causing diarrhea, and wheezing if the airways are blocked.
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The Laboratory Test For CgA
The laboratory test for CgA is ordered when the physician suspects that the patient might have a tumor such as a pheochromocytoma of the adrenal gland.which is cancer in the adrenal gland. This is the main reason the test is requested is in the case of these carcinoid tumors of the adrenal medulla. As this organ produces this protein in the largest concentration in the body, a carcinoid tumor can elevate CgA levels. In other cases, the physician will ask the laboratory to check the level of chomogranin A when cancer of the aorta, lung, and pancreas are suspected.
This laboratory test for CgA levels is performed by a nurse taking a sample of blood from the arm. The blood is checked for the level of CgA in the plasma. A higher than normal concentration of the protein would suggest that a tumor is present. However, the amount of chromogranin A measured is not directly related to how severe the disease might be, but rather the size of the tumor present. The normal level in the plasma is 20 u/l but this can go into the thousands if a large tumor is present.
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Web Source: Mount Nittany Medical Center. "Chromogranin A Test" 2009. Available: http://www.mountnittany.org/wellness-library/healthsheets/documents?ID=752