Chromogranin A (CgA) is a protein produced by neuroendocrine cells throughout your body. It’s stored inside tiny compartments called secretory granules and released alongside hormones and neurotransmitters. In clinical medicine, CgA is primarily used as a blood test to help detect and monitor neuroendocrine tumors, a group of cancers that arise from hormone-producing cells.
What CgA Does in the Body
Neuroendocrine cells are scattered across many organs, including the adrenal glands, thyroid, parathyroid, gut, and pancreas. These cells package their hormones into dense-core granules before releasing them into the bloodstream. CgA is the most abundant protein inside those granules. It isn’t just a passive bystander: it actually drives the formation of the granules themselves by aggregating in the acidic interior of each vesicle and causing the cell’s internal membranes to bud off into new storage compartments.
The adrenal medulla, the inner core of your adrenal glands, is the largest single source of CgA in circulation. There, CgA is stored and released together with catecholamines (adrenaline and noradrenaline). Plasma CgA levels correlate positively with catecholamine release and, by extension, with blood pressure. CgA also acts as a precursor molecule. Once released, enzymes can clip it into several smaller bioactive peptides that influence blood vessel tone, immune responses, and calcium handling inside cells.
Why Doctors Order a CgA Blood Test
Because neuroendocrine tumor cells retain the secretory machinery of their normal counterparts, they pump out large amounts of CgA. A blood test measuring CgA is one of the most widely used general markers for these tumors. Sensitivity ranges from 60% to 100% depending on tumor type, with the highest detection rates seen in serotonin-secreting carcinoid tumors and gastrinomas, where CgA is elevated in virtually all cases. For pheochromocytomas (adrenal tumors), roughly 89% of patients show elevated levels. Neuroendocrine tumors of the small intestine are detected about 80% of the time, non-functioning pancreatic neuroendocrine tumors about 69%, and medullary thyroid cancer about 50%.
The test is most sensitive for tumors that originate in the midgut (the middle portion of the small intestine) compared with pancreatic neuroendocrine tumors. One notable exception is insulinomas, a type of functioning pancreatic tumor. In one study, patients with insulinomas had median CgA levels of about 65 ng/mL, only slightly above the healthy control median of around 53 ng/mL, making CgA a poor screening tool for that specific tumor type.
How CgA Levels Reflect Tumor Burden
CgA isn’t just useful for diagnosis. The level in your blood tends to rise in proportion to the amount of tumor present in the body. Research on non-functioning pancreatic neuroendocrine tumors with liver metastases found a nonlinear, exponential relationship between tumor volume in the liver and CgA concentration. In other words, small increases in tumor bulk can produce disproportionately large jumps in CgA.
Higher CgA also signals a worse outlook. Patients whose baseline CgA exceeded 2.5 times the upper limit of normal had significantly shorter overall survival. And changes over time matter too. Patients whose CgA rose during treatment had markedly shorter progression-free survival than those whose levels stayed stable or fell. Clinicians use specific thresholds to interpret these changes: a drop of 50% or more from baseline suggests a meaningful treatment response, an increase of 25% or more suggests disease progression, and anything in between is considered stable.
Conditions That Raise CgA Without Cancer
A high CgA result does not automatically mean cancer. Several common, non-malignant conditions elevate the protein and can produce misleading results.
- Chronic atrophic gastritis: Destruction of acid-producing stomach cells triggers a compensatory rise in the hormone gastrin, which in turn stimulates neuroendocrine cells in the stomach lining to proliferate and release more CgA.
- Heart failure: The heart muscle itself produces CgA. In chronic heart failure, levels climb in parallel with the severity of cardiac dysfunction and can independently predict mortality.
- Kidney disease: The kidneys help clear CgA from the blood. Reduced kidney function slows that clearance, causing levels to accumulate.
- High blood pressure: Because CgA is co-released with adrenaline and noradrenaline, sustained hypertension can raise circulating levels.
- Liver failure: Impaired liver function has also been linked to elevated CgA.
Any of these conditions can push CgA above the reference range and complicate interpretation, which is why doctors consider the full clinical picture rather than acting on a single lab value.
Proton Pump Inhibitors and False Elevations
One of the most common and avoidable sources of a falsely elevated CgA result is proton pump inhibitor (PPI) use. Medications like omeprazole, lansoprazole, and pantoprazole suppress stomach acid, which causes gastrin levels to rise. That extra gastrin stimulates the same neuroendocrine cells in the stomach wall, driving up CgA.
The elevation begins quickly. In one study, CgA rose in a significant stepwise pattern within just five days of starting PPI therapy at any dose, and levels were markedly elevated after six months of continuous use. The good news is the effect reverses quickly too: stopping the PPI for five days was enough to produce a significant drop in both CgA and gastrin. Most guidelines recommend discontinuing PPIs at least two weeks before a CgA blood draw to avoid interference.
How to Prepare for the Test
Accurate CgA results depend on a few preparation steps. If you take a PPI, your doctor will typically ask you to stop it at least two weeks before the blood draw. If you’re on a somatostatin analog (a medication commonly used to manage neuroendocrine tumors), the timing of your blood draw relative to your injection schedule matters and should be coordinated with your care team.
Healthy individuals generally have CgA levels in the range of roughly 40 to 95 ng/mL, though exact reference ranges vary by laboratory and assay method. Because there is no single universal cutoff, your result is best interpreted by the doctor who ordered it, in the context of your symptoms, imaging, and medical history.
Other Biomarkers Tested Alongside CgA
CgA is rarely used in isolation. For small bowel neuroendocrine tumors, doctors often measure urinary 5-HIAA (a breakdown product of serotonin), neurokinin A, pancreatic polypeptide, and neuron-specific enolase. For pancreatic neuroendocrine tumors, CgA is frequently paired with pancreatic polypeptide and, if the tumor is functional, with the specific hormone it overproduces (insulin, gastrin, glucagon, or others).
Pancreastatin, a smaller peptide that is actually clipped from the CgA molecule itself, has gained attention as a complementary marker. Because pancreastatin levels are not affected by PPI use the way full-length CgA is, it can be a useful alternative when stopping a PPI is not practical. Elevated pancreastatin before surgery has been linked to shorter progression-free and overall survival in both pancreatic and small bowel neuroendocrine tumors, giving it prognostic value beyond what CgA alone provides.