MSACL 2019 EU Abstract

LC-MS/MS Analysis of Plasma Metanephrines Free of Interference from Midodrine and Metformin

Matthew J Whitlock, Amal Bashir, Emma L Williams
Department of Clinical Biochemistry, North West London Pathology, Charing Cross Hospital, Fulham Palace Road, London, W6 8RF

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Matthew Whitlock (Presenter) North West London Pathology

Relevant Financial Disclosures (within past 24 months) No relevant financial relationship(s) to disclose. Conflict mitigation NOT REQUIRED.

INTRODUCTION: Plasma metanephrines are recommended as one of the first line biochemical tests for the diagnosis of phaeochromocytomas and paragangliomas. LC-MS/MS methods are typically less susceptible to analytical interference than other methods, such as HPLC. However, analytical interference from midodrine, a sympathomimetic, and metformin, has been reported in LC-MS/MS assays for plasma metanephrines, affecting the ability to accurately quantitate metanephrine. We report an LC-MS/MS method for plasma metanephrines that has been demonstrated to be free of interference from midodrine, its metabolite, desglymidodrine, and from metformin.
METHODS: Metanephrine analysis was performed on a Waters Xevo TQ-XS in ESI positive mode following offline solid-phase extraction and separation on a Waters ACQUITY HILIC UPLC BEH Amide column. Separate plasma pools were spiked with known concentrations of midodrine and desglymidodrine and analysed in triplicate. Mean metanephrine (MN), normetanephrine (NMN) and 3-methoxytyramine (3-MT) concentrations were compared to mean results from triplicate analysis of the original plasma pool. Recovery of metanephrines was calculated in order to assess the interaction of the pro-drug and metabolite with the quantitation of metanephrines. Patient samples known to contain metformin were also analysed with an additional MRM transition (130.1>70.9) to detect the presence of metformin and determine the effect on the ionisation of metanephrine.
RESULTS: Averaged recovery of MN, NMN and 3-MT at each midodrine spike concentration were as follows; 105.1%, 98.5% and 101.7% (8.5 nmol/L), 103.8%, 100.4% and 101.2% (17 nmol/L) and 100.6%, 100.0% and 100.8% (34 nmol/L). Averaged recovery of MN, NMN and 3-MT at each desglymidodrine concentration were as follows; 99.0%, 100.2% and 103.7% (6.25 nmol/L), 99.0%, 100.5% and 100.9% (12.5 nmol/L) and 98.3%, 99.3% and 102.1% (25 nmol/L). Analysis of plasma from patients on metformin treatment demonstrated a peak in the 130.1>70.9 transition that was resolved from MN, NMN and 3-MT peaks, eluting at 3.19 minutes.
CONCLUSION: Midodrine and metformin are treatments used for patient groups in which plasma metanephrine analysis may be used in the investigation of orthostatic hypotension and hypertension, respectively. The LC-MS/MS method described has been shown to be free of interference from midodrine, desglymidodrine and metformin, permitting the accurate determination of metanephrine, normetanephrine and 3-methoxytyramine in patients on these medications.