Chromogranin A (CgA) Test: Uses & Normal Levels

What Is Chromogranin A?

Chromogranin A (CgA) is a protein produced by neuroendocrine cells — the specialized cells that act as the body’s hormonal messengers. When I see a patient with unexplained flushing, chronic diarrhea, or a family history of neuroendocrine tumors, one of the first tests I consider is the CgA level. It’s a highly sensitive marker for these rare but often manageable tumours.

When Is the CgA Test Ordered?

The test is primarily used to help diagnose neuroendocrine tumors (NETs), such as carcinoid tumors, pheochromocytoma, and small cell lung cancer. It is also invaluable for monitoring treatment response and detecting recurrence after surgery. My patients typically ask, “Will this test tell me if I have cancer?” I explain that CgA is a supportive tool — never a standalone diagnosis — but significantly raises suspicion when combined with imaging and symptoms.

Normal Reference Ranges for Chromogranin A

Reference ranges can differ slightly between laboratories. Below is a typical guideline used in many clinical settings. The standardized LOINC code for this test is 20655-4.

Note: Levels may rise slightly with age. Always compare your result to your own lab’s reference interval.

How to Prepare for a Chromogranin A Test

Fasting for 8–12 hours is often recommended, but the most important step is to avoid proton pump inhibitors (PPIs) for at least 5 days before the test. PPIs, used for heartburn or GERD, can artificially elevate CgA. I frequently hear, “Do I need to stop my stomach medication?” and the answer is yes — but only under your doctor’s guidance.

Factors That Can Affect CgA Levels

Several non‑cancer conditions can raise CgA: chronic gastritis, inflammatory bowel disease, liver cirrhosis, and even pregnancy. Stress and vigorous exercise can also cause mild elevation. Always provide your doctor with a complete medication and health history.

What High Levels Mean

A significantly elevated CgA — for instance, above 300–500 ng/mL — suggests the presence of a neuroendocrine tumor. However, modest rises (100–200 ng/mL) often reflect benign causes like PPI use or kidney disease. In my practice, I tell patients, “A high number is a strong signal, not a verdict.” Further imaging (CT, MRI, or octreotide scan) is essential for confirmation.

What Low Levels Mean

Low or undetectable CgA is usually not a concern. It may occur in people with auto‑immune polyendocrine syndrome or following successful treatment of a NET. There is no specific “danger” associated with low levels.

Chromogranin A During Pregnancy

Pregnancy can cause a modest physiological increase in CgA, typically remaining under 200 ng/mL. If a pregnant patient has a history of NET, the test is still useful but must be interpreted with caution. Your obstetrician and oncologist should work together.

Is High Chromogranin A Dangerous?

A high CgA itself does not cause symptoms — it’s a marker. The danger lies in the underlying condition, usually a neuroendocrine tumor. Early detection and treatment dramatically improve outcomes. If your level is high, don’t panic; trust your care team to guide the next steps.