Chromogranin A Test

General Description

The Chromogranin A (CgA) test is a type of biochemical analysis aimed at measuring the concentration of chromogranin A in the blood.

Chromogranin A is a protein that belongs to the granin family, a group of acidic proteins located in the secretory granules of neuroendocrine cells. CgA regulates the storage and secretion of hormones and neuropeptides and serves as a precursor for several functional peptides that modulate neuroendocrine function. Also known as parathyroid secretory protein 1, it is encoded by the CHGA gene. Normal blood levels of CgA range between 19.1 ng/mL and 98.1 ng/mL.

When Is It Indicated?

Chromogranin A is a type of tumor marker: an elevated CgA level in the blood suggests the presence of neuroendocrine, gastrointestinal, and pancreatic tumors, including carcinoids, pheochromocytomas, neuroblastomas, medullary thyroid carcinomas, and some pituitary tumors.

Additionally, CgA levels may also be elevated in certain tumors not derived from neuroendocrine tissues, such as small cell lung carcinoma or prostate cancer.

Therefore, the Chromogranin A blood test is indicated when symptoms compatible with a neuroendocrine tumor are present and are not caused by another condition, such as:

• Fatigue
• Weight loss
• Loss of appetite
• Nausea
• Diarrhea
• Abdominal pain
• Skin flushing
• Palpitations, tremors
• Sweating
• Digestive difficulties
• Frequent urination
• Increased thirst
• Behavioral changes, such as depression or irritability

Furthermore, the CgA test is used to assess the effectiveness of tumor treatment and to detect potential recurrences.

How Is It Performed?

To conduct a Chromogranin A test, a blood sample must be taken from the patient. The sample is obtained through venipuncture, usually from the arm, with a typical collection volume of 2 mL.

Once extracted, the sample is analyzed in the laboratory using different immunological methods to quantify the CgA concentration in the blood, including:

• Radioimmunoassay (RIA): Based on the specific interaction between an antibody and an antigen. This method involves adding a known amount of CgA labeled with a radioisotope to the blood sample, followed by the addition of CgA-specific antibodies that bind to both the labeled and unlabeled protein present in the sample. After a separation process, the amount of released radioactivity is proportional to the CgA concentration in the sample.
• Enzyme-Linked Immunosorbent Assay (ELISA): Also based on antigen-antibody complex formation. This method involves adding a specific antibody (capture antibody) to the blood sample, which binds to certain antigenic determinants of CgA. A second antibody, labeled with an enzyme (detection antibody), is then added, also binding to CgA. The resulting immune complex is detected and quantified by adding a specific substrate that triggers an enzymatic reaction, producing a color change.

Risks

Blood sample collection poses no significant risk to the patient, although a small bruise may develop at the puncture site.

However, it is important to emphasize that the Chromogranin A test, like any tumor marker test, is not a definitive diagnostic test but rather a tool that aids diagnosis and must be complemented with other evaluation methods. This is due to its limited specificity: blood CgA levels may be altered by non-cancerous conditions such as atrophic gastritis, heart failure, or chronic inflammation, as well as by certain medications, including proton pump inhibitors or H₂ blockers.

What to Expect From a Chromogranin A Test

The blood sample is collected in an extraction room. It is a very simple procedure that takes only a few minutes. Before inserting the needle, the area is disinfected, and an elastic band is applied to facilitate vein filling and improve puncture accuracy. During insertion, a slight pain may be felt. Once the sample is collected, the elastic band is removed, and a sterile dressing is applied with slight pressure for a few minutes to stop the bleeding. The patient can then resume normal activities.

If the test results show excessively high CgA levels, additional tests will likely be ordered to confirm or rule out the presence of neuroendocrine tumors. These may include hormone analyses, biopsies, or imaging tests.

Specialties that Request the Chromogranin A Test

The Chromogranin A blood test is typically requested in endocrinology and oncology consultations.