Chromogranin is a family of proteins found inside the storage compartments of cells that produce hormones and neurotransmitters. The most clinically important member, chromogranin A (CgA), acts as both a structural protein that helps package hormones for release and a blood test marker used primarily to detect and monitor neuroendocrine tumors. If your doctor ordered a chromogranin A test, it was likely to evaluate a suspected hormone-producing tumor or track one already diagnosed.
What Chromogranin Does in the Body
Chromogranin A is produced by endocrine, neuroendocrine, and nerve cells throughout the body. It lives inside tiny sacs called secretory granules, where hormones and signaling molecules are stored until the body needs them. When a cell receives the signal to release its contents, chromogranin gets released alongside the hormones, which is why its levels in the blood reflect how active these cells are.
Inside those granules, chromogranin A plays several roles. It helps the granules form in the first place by aggregating in the acidic interior of the cell’s packaging system and essentially “budding off” new storage compartments. Without it, cells produce fewer granules and store less of their hormones. Studies in mice lacking the chromogranin A gene show reduced hormone storage in adrenal cells, the glands that sit on top of your kidneys and release stress hormones like adrenaline.
Chromogranin A also acts as a calcium reservoir. The granules it fills are the cell’s main internal calcium storage sites, holding calcium concentrations around 2 to 4 millimolar. This matters because calcium is the trigger that tells cells to release their contents. By binding and releasing calcium readily, chromogranin helps regulate the timing of hormone secretion. It also sorts hormones away from other proteins during packaging, ensuring the right molecules end up in the right compartments.
The Chromogranin Family
Chromogranin A is the most studied member, but it belongs to a larger group called granins. The family includes chromogranin B and at least seven other related proteins known as secretogranins. All share similar traits: they’re acidic, soluble, and capable of binding calcium. When chromogranin A is absent, the body compensates by ramping up production of chromogranin B and several secretogranins, suggesting these proteins have overlapping backup functions.
Chromogranin A also functions as a precursor, meaning the body can break it down into smaller bioactive fragments that have their own effects on blood pressure regulation, immune response, and other processes.
Why Doctors Order a Chromogranin A Test
Because neuroendocrine cells produce chromogranin A, tumors that arise from these cells tend to flood the bloodstream with it. This makes CgA the most widely used blood marker for neuroendocrine tumors (NETs), particularly those originating in the gastrointestinal tract and pancreas. Normal blood levels typically fall between 19 and 98 ng/mL, though reference ranges vary somewhat between laboratories.
The test serves two main purposes. First, it helps with diagnosis. When compared against healthy individuals, a CgA cutoff of 18 to 19 U/L identifies neuroendocrine tumors with about 85% sensitivity and 96% specificity. That means it catches most cases while producing relatively few false alarms in healthy people. Second, the test tracks disease progression. Higher CgA levels generally correlate with more advanced disease. In patients with midgut carcinoid tumors, for example, those with CgA levels above 75 nmol/L had a five-year survival rate of 22%, compared to 63% for those below that threshold. The highest CgA levels tend to appear in patients with functioning ileal tumors, carcinoid syndrome, or liver metastases.
Beyond neuroendocrine tumors, elevated CgA has been observed in several other cancers, including small cell lung cancer, pheochromocytoma (a tumor of the adrenal gland), medullary thyroid cancer, neuroblastoma, and advanced prostate cancer. In prostate cancer specifically, high CgA levels are associated with more aggressive disease and later stages.
What Can Cause a False Elevation
One of the biggest limitations of the chromogranin A test is that many non-cancer conditions raise levels, sometimes significantly. The most common culprit is proton pump inhibitors, the widely prescribed heartburn medications like omeprazole and pantoprazole. PPIs suppress stomach acid, which triggers the stomach to produce more of a hormone called gastrin. That gastrin stimulates the growth of certain stomach cells that produce chromogranin A, artificially inflating blood levels. If you’re taking a PPI before a chromogranin test, your doctor will typically ask you to stop the medication or switch to a different type of acid reducer for at least two weeks before retesting.
Other non-tumor causes of elevated chromogranin A include:
- Kidney disease: Reduced kidney function slows the clearance of CgA from the blood, causing levels to accumulate.
- Chronic atrophic gastritis: This condition, where the stomach lining thins over time, independently raises CgA through a mechanism similar to PPI use.
- Heart failure and cardiovascular disease: Patients with chronic heart failure, hypertension, or acute coronary syndrome often show elevated CgA. In one study of 160 patients with chronic heart failure, CgA levels were significantly higher than in healthy volunteers.
- Inflammatory bowel disease: Both Crohn’s disease and ulcerative colitis can elevate levels.
- Liver disease: Chronic hepatitis, liver cirrhosis, and pancreatitis are also associated with higher readings.
These overlapping causes mean that a single elevated CgA result is never enough to diagnose cancer on its own. When distinguishing neuroendocrine tumor patients from the broader pool of people who might have elevated levels for other reasons, the test’s sensitivity drops to about 75% at a specificity of 84%. Doctors interpret CgA results alongside imaging, symptoms, and other lab work.
How the Test Fits Into Diagnosis and Monitoring
Chromogranin A is most valuable not as a standalone screening tool but as part of an ongoing monitoring strategy. For patients already diagnosed with a neuroendocrine tumor, rising CgA levels can signal disease progression or recurrence, while falling levels after treatment suggest a good response. The test is particularly useful for tumors that don’t produce other measurable hormones, since CgA is released by nearly all neuroendocrine tumor types regardless of what specific hormones they secrete.
For distinguishing limited disease (confined to the original site or liver) from widespread disease, a CgA cutoff around 281 to 282 U/L correctly classifies patients about 71% of the time. Higher thresholds improve confidence but miss more cases. At a cutoff of roughly 564 to 603 U/L, the test is 95% specific for diffuse disease but only catches 55% of those patients.
If you’ve received an elevated chromogranin A result, the first step is usually ruling out the common non-cancer causes, especially PPI use and kidney function. A result that remains elevated after addressing those factors warrants further investigation with imaging studies or additional biomarkers.