A novel immunoprecipitation-based targeted liquid chromatography-tandem mass spectrometry analysis for accurate determination for copeptin in human serum.

Objectives: Copeptin, a stable and simple-to-measure surrogate marker for arginine vasopressin (AVP), demonstrates excellent clinical values, particularly in diagnosing polyuria-polydipsia syndromes. However, conventional immunoassay methods are limited and lack comparability. Our aim was to establish a targeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for quantifying copeptin in human serum.

Methods: Copeptin was extracted from serum using immunoprecipitation, digested with trypsin, and prepared using anion exchange solid-phase extraction before LC-MS/MS detection. The analytical performance was validated in accordance with current guidelines. The method was compared to an immunofluorescent assay on the B.R.A.H.M.S platform.

Results: The LC-MS/MS method had a runtime of 8.5 min. The within-run precision ranged from 5.2 to 12.1 %, and total coefficients of variation ranged from 8.1 to 13.5 %. Copeptin quantitation showed linearity within the range of 5-1,000 pg/mL, with a limit of detection of 2.5 pg/mL. Recovery rates ranged from 95.2 to 103.1 %, and no significant matrix effect was observed with internal standard correction. The LC-MS/MS method had a good consistency with the immunoassay (r=0.926, slope=0.989). The reference interval for healthy individuals was 3.66-58.25 pg/mL.

Conclusions: We demonstrated the accuracy and reliability of this targeted LC-MS/MS method for quantifying copeptin. This innovative application showed satisfactory precision, a wide linear range, and a low limit of detection. Clinical studies are anticipated to be conducted to assess diagnostic accuracy using this method.