Chromogranin A is a protein released from neuroendocrine cells. These are cells that secrete hormones in response to signals from the nervous system. They are found in organs throughout the body. This test measures the amount of chromogranin A in the blood.
Neuroendocrine cells, and the endocrine glands that they are found in, can give rise to a variety of tumors, both benign and malignant. Examples include carcinoid tumors, insulinomas, small cell lung cancers, and neuroblastomas.
Many of these tumors release large quantities of the hormone associated with that tissue, either continuously or intermittently, causing symptoms characteristic for that tumor. However, not all neuroendocrine tumors release the expected hormones. In either case, neuroendocrine tumors are frequently associated with increased concentrations of CgA.
Carcinoid tumors are slow-growing noncancerous or cancerous masses that form mainly in the gastrointestinal tract (especially in the appendix) and in the lungs. According to the American Cancer Society, there are about 8,000 gastrointestinal and 4,000 lung carcinoid tumors diagnosed each year in the United States. Many more of these tumors may exist, but most remain small and do not cause any symptoms.
When carcinoid tumors are discovered in asymptomatic patients during surgical procedures performed for other reasons, they are called "incidental" tumors. A small percentage of these tumors may eventually grow large enough to cause obstructions in the intestines or bronchial tubes of the lungs.
The best-characterized circulating biomarker that identifies NETs in general is CgA. Monitoring blood CgA levels may effectively provide information that is helpful in delineating tumor burden and rate of tumor growth, predicting tumor response to therapy and providing some indication as to prognosis.
As of April 19, 2021, Quest uses a liquid chromatography-tandem mass spectrometry (LC/MS/MS)-based assay to measure chromogranin. Previously, chromogranin A was measured using an enzyme-linked immunosorbent assay (ELISA).
Typically, chromogranin A levels are around 2.5 times higher with the LC/MS/MS assay - this relationship is captured by the following equation: ELISA result = 13.6 + 0.36 × LC/MS/MS result; correlation coefficient = 0.71.
Reference intervals with both methods:
Elisa Method ( old method ): 25-140 ng/mL
LC/MS/MS Method ( new method ): < 311 ng/mL
References:
Weber DM, Yang JY, Goldman SM, Clarke NJ, Taylor SW, McPhaul MJ. Antibody-Free Quantification of Serum Chromogranin A by Targeted Mass Spectrometry. Clin Chem. 2021 Nov 26;67(12):1618-1627. doi: 10.1093/clinchem/hvab191. PMID: 34718463.