In general it can be stated that practically all carcinoid syndrome cases exhibit some increase in at least one of the many endocrine chemical products elaborated by the tumor and producing the syndrome. These include not only blood serotonin and urine 5HIAA but also chromogranin A, Neuron Specific Enolase, Pancreatic Polypeptide, Calcitonin, Substance P, Neurokinin A, Prostaglandin A,E and D, Histamine and Pancreastatin.
Furthermore there are a number of look alike syndromes such as Zollinger Ellison, VIPoma and Mast Cell Disease which can mimic carcinoid and be suspected by respectively measuring Gastrin, VIP, Histamine and Tryptase. Medullary Thyroid Carcinoma can cause a carcinoid-like syndrome and usually produce Calcitonin, CEA and at least one of the prostaglandins. Certain pituitary tumors make prolactin and can be associated with carcinoid like features. Prolactin is useful in this diagnosis.