Performance evaluation of serum IgG subclass quantification using a SPAPLUS turbidimetric analyzer and comparison with the BNII nephelometer

Abstract

IgG consists of four subclasses: IgG1, IgG2, IgG3, and IgG4. Changes in the serum concentration of each subclass reflect different clinical situations, and quantification of each subclass is important to assess patients’ clinical states. Herein, we evaluated the analytical performance of the SPAPLUS turbidimetric analyzer (The Binding Site, Birmingham, UK) for IgG subclass. Precision, linearity, comparison with the BNII system (Siemens Healthineers, Erlangen, Germany), and reference interval were assessed according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. The repeatability and within-laboratory precision were within 5% for all IgG subclasses. The coefficient of determination (R2) was higher than 0.99 for the analytical measurement range in all IgG subclasses. Comparison between SPAPLUS and BNII revealed significant differences in IgG1, IgG3, and IgG4 (p < .0001). IgG1 and IgG4 values were lower in SPAPLUS than BNII. On the other hand, IgG3 values were higher in SPAPLUS than BNII. The SPAPLUS turbidimetric analyzer exhibited good analytical performance for quantification of four IgG subclasses. Because of the differences between SPAPLUS and BNII, follow-up test for disease monitoring should be performed with same instrument.