The Chromogranin A (CgA) test measures this protein in the blood, primarily used as a tumor marker to detect, monitor, and assess the progression of Neuroendocrine Tumors (NETs), like carcinoids, as CgA is released by these cells. Elevated levels can signal tumor presence, recurrence, or resistance to treatment, helping doctors diagnose, manage treatment response, and predict outcomes for conditions affecting neuroendocrine cells in the pancreas, adrenals, and gut