METANEPHRINES (Free), PLASMA (METANEPHRINE and NORMETANEPHRINE)

3mL EDTA blood

Recommended collection:
Draw from fasting patient at supine position after 20-30min of rest

​Keep cold with ice and send immediately to the laboratory.

​Liquid Chromatography - Tandem Mass Spectrometry (LC-MS/MS)

​From 0 day:
Metanephrine : < 0.33 nmol/L
Normetanephrine : < 0.71 nmol/L

Plasma metanephrine and normetanephrine reference intervals  (URL 97.5th percentile value) are from Eisenhofer et.al 2013 Annals Clin Biochem 50:62-69; above URLs used together demonstrated 93.9% sensitivity and 88.3% specificity.

Mean = 7 days, Range: 3 – 11 days

​Wednesday

​Studies have suggested that age-specific / age-group specific reference intervals for plasma normetanephrine used in conjunction with metanephrine improved specificity and sensitivity for the diagnosis of phaechromocytoma. A curvilinear algorithm equation to calculate age-specific reference intervals for plasma normetanephrines was derived by Eisenhofer et.al (2013).

Age-group specific reference intervals (using the first age of each group)  obtained from the curvilinear algorithm is reproduced here. Used together with plasma metanephrine URL of 0.45 nmol/L has demonstrated 93.6% sensitivity and 96% specificity

5-17yr:                  0.54 nmol/L

18-29yr:                0.55 nmol/L

30-39yr:                0.60 nmol/L

40-49yr:                0.67 nmol/L

50-59yr:                0.80 nmol/L

>60yr:                   0.99 nmol/L

Rao et.al 2017 Eur J Endocrinol 177:103-113 using LC-MS/MS in their study verified the use of age-specific reference intervals (NMET) in diagnosis. Additionally, the use of methoxytyramine (MTY) assists with positive confirmation.

Patient Preparation:

Subjects should abstain from caffeine, acetoaminophen,  before testing. The following drugs: (on MET, NMET, MTY) isoproterenol,  ephedrine, (on MTY) metamphetamine also interferes with the analysis technique.