Plasma metanephrine

Cut-offs vary with the laboratory and with whether the sample was taken lying or seated (seated cut-offs are higher), so the printed cut-off is the one to use.

Metanephrine is the breakdown product of adrenaline, the hormone the adrenal glands release in a fright or under stress. Measuring the breakdown product in blood is more reliable than measuring adrenaline itself, because it is released steadily rather than in bursts. It is the main blood test for a rare adrenal tumour called phaeochromocytoma.

It is requested, together with normetanephrine, when episodes of headache, sweating and palpitations with high blood pressure are being looked into, when an adrenal lump is found on a scan, when blood pressure is difficult to control, and in families with inherited tumour conditions.

• Phaeochromocytoma and related tumours, which make adrenaline and its breakdown products
• Stress, pain, anxiety and a difficult blood draw
• Sitting up rather than lying down for the sample
• Some medicines, including certain antidepressants, decongestants and levodopa
• Caffeine, nicotine and recent heavy exercise
• Sleep apnoea and acute illness

• A value below the cut-off is the expected finding
• Some blood pressure tablets can lower it slightly
• After removal of a phaeochromocytoma the expected level is below the cut-off

• A stressful blood draw or sitting up for the sample can push it above the cut-off
• Caffeine, nicotine, paracetamol on some older methods and several common medicines interfere
• Sleep apnoea and acute illness raise it

Ideally taken after lying quietly for 20 to 30 minutes, fasting, without caffeine, nicotine or strenuous exercise beforehand. Some medicines are paused first under medical supervision. It is sent to a specialist laboratory and is usually reported with normetanephrine and sometimes 3-methoxytyramine.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.