[Establishment and application of quantitative immunoassay method based on stable element labeling and inductively coupled plasma mass spectrometry].

Objective: To establish a quantitative immunoassay method based on stable element labeling and inductively coupled plasma mass spectrometry (ICP-MS) for the detection of serum amyloid A (SAA) and evaluate its performance. Methods: An immunoassay system based on sandwich method was established with magnetic bead as carrier and holmium (Ho) as element tags. The binding ratio of hydrophilic streptavidin magnetic beads and biotinylated antibody, the amount of elemental antibody, and the reaction time were optimized to choose the optimal reaction conditions. According to the documents of Clinical and Laboratory Standards Institute (CLSI), the analytical performance was evaluated, including the limit of blank (LOB), linearity, accuracy, specificity, imprecision and interference test. Finally, 82 SAA plasma samples were collected after the turbidimetric inhibition immunoassay, and the newly established method was used for detection. Moreover, the detection results of the two methods were analyzed by Pearson correlation analysis. Results: The optimal binding ratio of hydrophilic streptavidin and biotinylated antibody was 1∶0.15, the amount of Ho-labeled antibody was 3 µl and the incubation time of the two reaction steps was 40 min and 30 min, respectively. The LOB was 0.6 ng/ml. The linearity was good within the range of 0-1 200 µg/L (R2=0.998 9, P<0.001). The inter-batch precision of high-value samples and low-value samples was 9.42% and 7.95%, respectively, and the intra-batch precision was 14.56% and 13.56%, respectively. The recovery was 96.01%-104.76%. The cross-reaction rates with procalcitonin (PCT) and C-reactive protein (CRP) were 0.45% and 0.015%, respectively. When the concentration of triglyceride≤35.5 mg/L, bilirubin≤0.52 mg/L and hemoglobin≤2.4 g/L, the interference bias was less than 10%. The results of 82 SAA plasma samples were 12.65 (4.45, 59.03) mg/L by ICP-MS immunoassay and 18.23 (9.33, 68.72) mg/L by turbidimetric inhibition immunoassay, respectively. The newly established system was well correlated with turbidimetric inhibition immunoassay (R2=0.983, P<0.001). Conclusion: The quantitative immunoassay for SAA with Ho as marker established in this study has high precision, good accuracy, high specificity, and wide linear range, which can meet the clinical testing requirements.