The chromogranin test is a test that measures the levels of chromogranin A (CgA) in the body. CgA is a protein that is produced by the body’s cells and is found in high levels in certain types of cancer, such as neuroendocrine tumors. The test can be used to help diagnose these tumors, as well as to monitor treatment and check for tumor recurrence.
The test is usually done with a blood sample, but it can also be done with a tissue sample. In order to determine whether a fast is needed before a chromogranin A test, we will need to review some basic physiology concepts. But before then, we found this short youtube video from the Neuroendocrine Tumor Research Foundation to be a very useful for patients with NETs undergoing this test.
https://youtu.be/pzI1MObqF-4
Structure and function of chromogranin A
Chromogranin A (CgA) is a protein that is found in various tissues throughout the body, including the pancreas, adrenal glands, and intestine. CgA is a member of the chromogranin family of proteins, which are all involved in the storage and release of catecholamines. CgA is structurally similar to other chromogranins, and contains three main domains: an N-terminal domain, a secretory granin domain, and a C-terminal domain. The N-terminal and secretory granin domains are responsible for the storage of catecholamines, while the C-terminal domain is involved in their release. CgA is also cleaved into smaller peptides, such as catestatin and chromostatin, which regulate the release of catecholamines. Chromogranin A is therefore an important protein in the endocrine system, and plays a role in a variety of physiological processes.
Metabolism of chromogranin A
Chromogranin A (CgA) is a protein that is found in high concentrations in the granules of chromaffin cells. CgA is involved in the storage and release of catecholamines, and it also has a role in cell growth and differentiation. CgA is metabolized by several different enzymes, including carboxypeptidase E (CPE), peptidyl glycine alpha-amidating monooxygenase (PAM), and prolyl endopeptidase (PE). CgA is also subject to post-translational modifications, such as glycosylation and phosphorylation. These modifications can affect the activity of CgA and its interaction with other proteins. Understanding the metabolism of CgA is essential for understanding its function in the body and its potential as a therapeutic target.
Elevation in chromogranin A
CgA is involved in the storage and release of catecholamines, such as adrenaline and noradrenaline. Plasma levels of CgA are generally low, but they can be elevated in certain conditions, such as renal failure, Hepatitis C, some types of cancer, and Pheochromocytoma. In most cases, an elevated CgA level is a marker for disease rather than a cause. However, in some rare cases, an elevation in CgA levels can be the result of certain medications, such as proton-pump inhibitors (PPIs) or lansoprazole.
How do proton pump inhibitors increase the levels of chromogranin A?
Chromogranin A (CgA) is a protein that is found in high levels in people with several types of cancer, including gastric cancer. Some studies have shown that PPIs can increase CgA levels, which may lead to false-positive results on tests for neuroendocrine tumors. The mechanism by which PPIs increase CgA levels is not fully understood, but it is thought that the reduction in stomach acid may cause an increase in the release of CgA from cells. This increase in CgA levels may then lead to false positive results on tests for neuroendocrine tumors.
How long should I stop proton pump inhibitors before my chromogranin A test?
The answer is two weeks.
Do you need to fast before the chromogranin A test?
Chromogranin A (CgA) is a protein that is secreted by the gastrointestinal tract and may be elevated after a meal.
References
Marotta V, Zatelli MC, Sciammarella C, Ambrosio MR, Bondanelli M, Colao A, Faggiano A. Chromogranin A as circulating marker for diagnosis and management of neuroendocrine neoplasms: more flaws than fame. Endocr Relat Cancer. 2018 Jan;25(1):R11-R29.
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