Development of a designed comparison method based on isotope dilution liquid chromatography–tandem mass spectrometry for determining plasma renin activity and its clinical assessment of renin activity stability in plasma

Plasma renin activity (PRA) is recommended as the first screening indicator for primary aldosteronism. Immunoassays and liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods have been developed for quantifying PRA, but the interchangeability across assays and laboratories was suboptimal, which predominantly related to the differences in the plasma incubation strategy. This study aims to establish and validate a designed comparison method based on LC-MS/MS. The sensitivity, matrix effect, precision, accuracy, and storage stability were validated according to the Clinical Laboratory Standard Institution (CLSI) C-62A guidelines. The plasma incubation procedure was optimized to achieve maximum PRA results. The short-term stability of PRA plasma was assessed at 4 °C and room temperature (RT) for specific time points. Differences from the baseline were calculated using a one-way analysis of variance. The designed comparison method for PRA measurement exhibits excellent performance characteristics. The results from the 2022 national external quality assessment scheme for PRA showed good consistency of the developed method with other LC-MS/MS methods (relative biases: -6.8% to 4.6%), which demonstrated the reliability of the established method. Two sets of generation buffers were optimized to maximize the renin activity. The acetate buffer was recommended to be used in laboratory practice due to better metrological sensitivity. PRA plasma is stable for one day at 4 °C and RT. In summary, a reliable, traceable, and reproducible LC-MS/MS method for determining PRA was well-established and validated. The recommended incubation protocol is hoped to reduce the discrepancy in Ang1 generation. The evaluated short-term stability for PRA plasma could provide flexibility in clinical practice.