Chromogranin A is a protein secreted in several environments. While it is primarily released in the adrenal medulla with catecholamines (norepinephrine, epinephrine, dopamine, and others), CgA is often found stored in the granules of endocrine cells in the GI tract. CgA is the precursor molecule for several active molecules. Vasostatin-1 and -2 are involved in regulation of various effects of the cardiovascular system, including blood pressure and stroke volume, by opposing the action of catecholamines. Catestatin decreases release of catecholamines. Pancreastatin decreases insulin secretion. A number of other molecules are also derived from CgA.
Chromogranin A and its derivatives are biomarkers for several conditions. 60-80% of neuroendocrine tumor patients demonstrated elevated chromogranin A. A connection with Alzheimer’s disease has recently been reported. Rheumatoid arthritis and lupus patients may have elevated CgA as a result of increased tumor necrosis factor. Various forms of cancer, kidney disease, and elevated cortisol can also impact chromogranin A level.
Elevated CgA has also been linked to a number of inflammatory GI conditions. 30-50% of IBD patients with active disease have elevated serum CgA. In ulcerative colitis, fecal chromogranins were elevated but not correlated with disease activity. Conflicting results have been seen in patients with Crohn’s disease. Some studies have reported an increased amount of CgA containing cells in patients with IBS.
There are a number of methods for quantifying chromogranin A. Proton pump inhibitors and H2 antihistamines can yield false positive results. A study compared several commercial kits for measuring chromogranin A and found that the radioimmunoassay (RIA) kit was most likely to be accurate with a sensitivity of 93% and specificity of 85%. This means that 93% of the time, this kit properly identified patients with high CgA as having high CgA, while 85% of the time, it properly identified patients with normal CgA as having normal CgA. Currently, there are multiple test methods for quantifying serum and plasma CgA with no central standardization.
Chromogranin A is a constituent of granules in rat mast cells. Tumor necrosis factor is a mediator released by mast cells and may also influence the levels of chromogranin A in mast cell patients. One study found that 31.5% of patients with mast cell activation disease (in a cohort mostly composed of MCAS patients) demonstrated elevation of serum CgA. This same study concluded that plasma heparin and 24 urine testing for prostaglandin D2 and 9a,11b-prostaglandin F2 were the most sensitive markers for mast cell activation with other mediators being less effective.
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