What is being tested?
Chromogranin A (CgA) 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 tumours, both benign and malignant. Examples include carcinoid tumours, insulinomas, small cell lung cancers, and neuroblastomas. The CgA test may be used to help detect, diagnose, and/or monitor neuroendocrine tumours, especially carcinoid tumours.
Many of these tumours release large quantities of the hormone associated with that tissue, either continuously or intermittently, causing symptoms characteristic for that tumour. However, not all neuroendocrine tumours release the expected hormones. In either case, neuroendocrine tumours are frequently associated with increased concentrations of CgA.
Carcinoid tumours are slow-growing noncancerous or cancerous masses that form mainly in the gastrointestinal tract (especially in the appendix) and in the lungs. 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" tumours. A small percentage of these tumours may eventually grow large enough to cause obstructions in the intestines or bronchial tubes of the lungs.
How is it used?
The chromogranin A (CgA) test is used as a tumour marker. It may be ordered in combination with a 5HIAA urine test to help diagnose carcinoid tumours. It may also be used to detect the presence of other tumours arising from neuroendocrine cells.
Neuroendocrine cells are cells that have both nerve and hormone (endocrine) aspects and are found in organs throughout the body. These cells and the endocrine system glands that they are found in can give rise to a variety of tumours, both benign and malignant. Examples include carcinoid tumours, insulinomas, small cell lung cancers, and neuroblastomas.
Many of these tumours release large quantities of hormones, such as serotonin, catecholamines, or insulin, continuously or intermittently, causing symptoms characteristic for that tumour. However, some neuroendocrine tumours do not release the expected hormones. In either case, neuroendocrine tumours are frequently associated with increased concentrations of CgA.
A CgA test may also be used to help monitor the effectiveness of treatment and detect recurrence of these tumours.
When is it requested?
A CgA test is ordered along with other tests when a healthcare practitioner suspects that a person's signs and symptoms are due to a carcinoid tumour or other neuroendocrine tumour.
Some signs and symptoms may include:
This test may be ordered periodically to help evaluate treatment effectiveness and monitor for tumour recurrence.
What does the result mean?
The level of chromogranin A in the blood is normally low. A person with no signs or symptoms and a normal level of CgA is unlikely to have a neuroendocrine tumour. However, the test is not perfect, and it is possible to have a neuroendocrine tumour even if the concentration of CgA is normal.
An increased CgA level in a person with symptoms may indicate the presence of a tumour, but it is not specific for the type of tumour or its location. In order to diagnose the condition, the tumour 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 tumour(s) that may be present.
Not all patients with a neuroendocrine tumour have typical signs and symptoms. Some tumours do not produce the hormone associated with that tissue or only produce it intermittently.
The concentration of CgA is proportional to the tumour burden - the mass of the tumour. If concentrations of CgA 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 tumour.
Is there anything else I should know?
CgA concentrations may be elevated in conditions such as liver disease, inflammatory bowel disease, renal insufficiency, and with stress. These possible causes for elevated CgA levels should be considered when interpreting test results. Chromogranin A can also be increased in people who take proton pump inhibitors (PPIs), which are drugs that reduce the amount of stomach acid.
There are currently no FDA-approved chromogranin A tests. Those CgA tests that have been developed and validated by laboratories are all slightly different, and their results are not interchangeable. When monitoring a patient over time, CgA tests should be performed by the same laboratory so that values can be compared.
Common questions
No. This test is usually ordered to help diagnose and monitor a carcinoid or other neuroendocrine tumour, both of which are uncommon. Most people will never need to have this test performed.
This is usually accomplished through the use of imaging scans such as x-rays, computed tomography (CT), or magnetic resonance imaging (MRI). In some cases, surgery is required to find the tumour. For more on these imaging tests, visit Inside Radiology.
In order to determine whether the tumour is benign or cancerous, the healthcare practitioner will need to perform a biopsy or remove the tumour surgically. The tumour is sent to the laboratory, where a pathologist examines the tumour cells under the microscope and makes a diagnosis. (For more on this, read the article on Anatomical Pathology)
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