Chromogranin A
Chromogranin A (CgA) is a major acidic glycoprotein that is co-stored and co-secreted with catecholamines and other peptide hormones in the secretory granules of neuroendocrine cells. Chromogranin A acts as a precursor to several smaller, biologically active peptides (such as vasostatin, pancreastatin, and catestatin) after undergoing enzymatic cleavage. Within the cell, it plays a crucial role in the generation of secretory granules and the regulation of hormone secretion. Because it is widely distributed throughout the neuroendocrine system, it serves as an excellent universal marker for neuroendocrine differentiation.
Parameters Measured
Preparation
Chromogranin A Test: Monitoring Neuroendocrine Tumours
Chromogranin A is a protein released by neuroendocrine cells scattered throughout the body cells that sit at the crossroads of the nervous and hormonal systems. When these cells turn cancerous, they tend to release far more CgA than usual, which makes this test a useful, if imperfect, tool for spotting and tracking neuroendocrine tumours (NETs).
What it's actually good for
CgA works best as a monitoring tool rather than a first-line screening test. Once a neuroendocrine tumour has been diagnosed, tracking CgA levels over time helps doctors see whether treatment is working or whether the tumour is progressing. It's particularly useful for pancreatic neuroendocrine tumours, where research has shown it distinguishes affected patients from healthy people fairly reliably, though it performs less consistently for a specific subtype called insulinomas.
The catch almost everyone runs into: PPIs
Here's something that trips up a lot of patients and, occasionally, doctors too. Common acid-reflux medications called proton pump inhibitors, or PPIs (things like omeprazole or pantoprazole, sold under many brand names), can cause CgA levels to shoot up dramatically without any tumour being involved at all. In one documented case, a patient's CgA reading was ten times the normal upper limit purely because of PPI use, and it returned to normal within weeks of stopping the medication. In a larger study of nearly 150 patients with falsely elevated CgA, PPI use was identified as the cause in over a third of cases.
Because of this, anyone taking a PPI is generally advised to stop the medication, if their doctor agrees it's safe to do so, for a period before this test, to avoid a misleading result. If stopping isn't an option, the elevated reading needs to be interpreted with that medication history firmly in mind.
No fasting is required for this test, though your doctor may ask about current medications beforehand.