Cells derived from neuroendocrine tumours (e.g. pheochromocytoma) are known to produce Catecholamines which are secreted episodically via vesicles into the blood stream.

But beside this a small portion of the Catecholamines is metabolized inside the cells to the corresponding catecholamines metabolites – namely Metanephrine (metabolite of Adrenaline), Normetanephrine (metabolite of Noradrenaline) and 3-Methoxytyramine (metabolite of Dopamine) – and then secreted at low levels continuously into the blood stream.
Recent studies and publications have shown that the combined quantification of plasma free Metanephrine (fMN) and plasma free Normetanephrine (fNMN) are the most accurate biochemical markers for the clinical diagnosis of pheochromocytoma and paragangliomas (PPGL) and allow the follow-up of pheochromocytoma patients.
LDN has developed enzyme immunoassays and isotopic assays for the quantitative determination of fMN and fNMN in human plasma.