Quantitation of plasma and urine 3-methoxytyramine using ID‑LC-MS/MS: A candidate reference measurement procedure and its application to evaluate the results from more than 100 routine LC-MS/MS labs in China.

BACKGROUND

Accurate measurement of 3-methoxytyramine (3MT) is essential for diagnosing metastatic pheochromocytomas, paragangliomas, and neurodegenerative diseases like Parkinson's disease. Despite the growing use of liquid chromatography-tandem mass spectrometry (LC-MS/MS) for 3MT quantification, poor comparability persists among laboratories. This study developed an isotope dilution LC-MS/MS-based candidate reference measurement procedure (cRMP) for plasma and urine 3MT measurement and evaluated LC-MS/MS results from over 100 laboratories in China.

METHODS

Plasma/urine samples were spiked with internal standard, followed by protein precipitation and solid-phase extraction. The final extract was analyzed using LC-MS/MS. The cRMP assigned values to four samples (202411-202414), which were sent on dry ice to over 100 laboratories in China for analysis using routine LC-MS/MS methods. Laboratory results were compared to cRMP-assigned target values.

RESULTS

The method validation of cRMP showed good precision, with intra-run and total imprecision ranging from 0.97% to 3.85% and 0.99% to 4.03%, respectively. The relative recovery rate ranged from 99.51% to 104.61%. Significant biases were observed when comparing the measurement results of routine laboratories with the target values assigned by cRMP, and the results from different laboratories were not comparable.

CONCLUSION

Our LC-MS/MS cRMP demonstrates high accuracy, precision, specificity, and sensitivity for 3MT measurements. By utilizing SI-traceable certified reference materials(3MT Cerilliant standard), it ensures robust traceability. This cRMP serves as a high-order standard for establishing traceability, calibrating routine methods, and developing reference materials, supporting the standardization of 3MT assays.