Endocrine Abstracts

Background: Plasma metanephrine analysis is widely accepted as the test of choice for phaeochromocytomas and sympathetic extra-adrenal paragangliomas. It is important to analyse 3-methoxytyramine along with metanephrine and normetanephrine as 3-MT measurement has been shown to be useful in tumour localisation and also in determining whether metastasis has taken place. 3-MT analysis is challenging as the concentrations of 3MT of interest are very low, and the sensitivity of many assays is not sufficient to distinguish between normal and raised concentrations. We have developed a sensitive method for measuring metanephrine, normetanephrine and 3-methoxytyramine using an online solid phase extraction system coupled to a Waters Xevo TQS mass spectrometer.

After sample dilution with internal standard, deproteinisation is carried out using 10 K centrifugal filters. 75 μl of deproteinised sample is loaded onto a Waters Acquity OSM system, using weak cation exchange cartridges for further on-line sample clean-up. Chromatography is carried out on a Waters Hilic 3 μm 2.1×50 mm column, and mass spectrometry is performed on a Waters Xevo TQS mass spectrometer.

The recovery of samples from the centrifugal filters was >95% for all 3 analytes at a concentration of 3 nmol/l. The LLOQ was 0.0375 nmol/l for metanephrine, and 0.075 nmol/l for normetanephrine and 3-MT. The assay was linear up to 30 nmol/l for all analytes, and a good correlation was shown between this assay and the assay currently in use in our laboratory for metanephrine and normetanephrine, with an r² value >0.99.

We have developed a sensitive assay for plasma metanephrine analysis, which correlates well with our current assay for metanephrine and normetanephrine. The LLOQ of 3MT is 0.075 nmol/l, which will enable us to distinguish between normal and raised levels, something which has not been possible with previous assays.