Several studies have shown that Chromogranin A is the most universally helpful marker that is found to be elevated in the circulation of about 90% of patients with metastatic neuroendocrine tumors. "The highest levels of serum chromogranin A (up to 1000 times the upper limit of the normal range) have been found in patients with metastatic carcinoid tumors. The stability of serum chromogranin A speaks favorably for its use in detecting carcinoid tumors and monitoring their progression; alternative diagnostic tests for carcinoid tumors include tests of urinary 5-hydroxyindoleacetic acid, serum serotonin (5-hydroxytryptamine), and serum neuron-specific enolase. In multiple endocrine neoplasia type I, there is a clear correlation between the tumor mass and the circulating level of chromogranin A. In patients with midgut carcinoid tumors, an elevated chromogranin A level is an independent predictor of death." [Laurent Taupenot, Ph.D., Kimberly L. Harper, M.D., and Daniel T. O'Connor, M.D; N Engl J Med. 2003 Mar 20;348(12): pp1134-49]

There are several excellent commercially-available kits which give reliable estimations of chromogranin A. Specific markers are useful for diagnosis also, and are helpful indicators of the effectiveness of treatment particularly where tumor bulk may not change so much as tumor activity. Sporadic pancreatic neuroendocrine tumours may secrete more that one peptide and this indicates worsening prognosis. Because of the wide variation in the progression of neuroendocrine tumors, a prognostic indicator gives a significant advantage to the clinician in order to facilitate optimum treatment at the optimum stage of disease. Both chromogranin A and neurokinin A have been used as powerful prognostic indicators for midgut carcinoid tumours.