The main theme of this thesis are rare neuroendocrine tumors and we describe the optimization of the current laboratory methods that are used in the diagnostic procedure for patients with a pheochromocytoma and the development of new diagnostic laboratory methods. Pheochromocytoma are rare neuroendocrine tumors that derive from the adrenal gland and secrete catecholamines. The metabolic end-products of the catecholamines can be measured as metanephrine and normetanephrine in plasma and urine. We showed that patients who underwent unilateral or bilateral adrenalectomy had a higher concentration of plasma normetanephrine and a lower concentration of plasma metanephrine. We recommend the use of adapted laboratory reference values in these patients. In addition, we have shown that the concentration of metanephrine and normetanephrine in plasma is not affected by commonly used blood pressure lowering medication, when determined with a very sensitive laboratory method. Furthermore, we studied the determination of metanephrines and normetanephrines in saliva, which could be useful in the future for children.
In addition to patients with pheochromocytoma, we also studied patients with head and neck paragangliomas. Head and neck paragangliomas are located in the head and neck region and consist of the same cells as pheochromocytomas. In only 28% of patients with these tumors an increased production of catecholamines is found. Therefore, we tested the sensitivity of a new marker, the dopamine concentration in blood platelets, in patients with these tumors. The new marker was more sensitive than the current method, 3-methoxytyramine in plasma, but not sensitive enough to replace it.