Chromogranin A is a protein that comes from neuroendocrine cells. These cells secrete hormones (gastrin, calcitonin, catecholamines, glucagon, 5-HIAA, PTH, etc.) in response to a signal from the nervous system, and they are found throughout the body (pancreas, stomach, intestine, adrenal glands, etc.). Neuroendocrine tumours generally cause the secretion of abnormally high levels of a hormone causing clinical symptoms that suggest their origin (redness (flushing) of the head and neck, diarrhea, nausea and vomiting, duodenal ulcers, hypertensive seizures, etc.). Most of these tumours also release chromogranin A. Sometimes, chromogranin A is the only sign of a neuroendocrine tumour.
A normal result in the absence of signs and symptoms indicates that a neuroendocrine tumour is unlikely to be present. A high result indicates the probable presence of a neuroendocrine tumour, but it does not determine the type. Further testing is required to locate and identify the type of tumour. A note appearing in each report indicates that levels can be falsely high in patients who have taken proton pump inhibitor medications to control stomach hyperacidity in the two weeks prior to the test (omeprazole, esomeprazole, pantoprazole, rabeprazole and lansoprazole under different commercial names).