Analytical and clinical performance evaluation of two POC tests for therapeutic drug monitoring of infliximab.

Background Infliximab (IFX) is an effective therapy in patients with inflammatory bowel disease. Serum IFX trough concentrations correlate well with clinical, biological and endoscopic outcomes. Therefore, therapeutic drug monitoring (TDM) of infliximab is useful for dose optimization and prevention of secondary treatment failure. In the present study, analytical and clinical performance of two point-of-care (POC) tests, RIDA®QUICK IFX Monitoring assay (R-biopharm) and Quantum Blue® Infliximab assay (Bühlmann), have been evaluated and compared to our established enzyme-linked immunosorbent assay (ELISA) (apDia IFX ELISA). Methods Analytical performance was assessed according to the CLSI EP5-A2 protocol using the manufacturer's kit controls and different serial dilution series. Method comparison with our established ELISA was done using a wide range of consecutive patient samples (n=180). Clinical concordance was evaluated by categorization based on well-known therapeutic cut-off points (3-7 µg/mL). Results The analytical performance of both POC tests was inferior to the established ELISA, but acceptable based on the manufacturer's quality claims. Eight-point serial dilution confirmed the analytical performance data in the low-level measuring range. Eleven-point serial dilution demonstrated linearity for both POC tests over the studied concentration range. Method comparison with the ELISA showed significant negative proportional bias for the RIDA®QUICK IFX Monitoring assay. However, good correlation and clinical concordance were shown. Quantum Blue® Infliximab assay showed a significant positive proportional and a negative systematic bias in comparison with the ELISA, resulting in overestimation of IFX levels with impact on clinical concordance data. Conclusions Both POC tests have their own specific benefits and drawbacks but are suitable for therapeutic drug monitoring of IFX. However, long-term monitoring of IFX trough levels requires measurement of IFX concentrations with the same assay.

Performance Evaluation of Serum Free Light Chain Analysis: Nephelometry vs Turbidimetry, Monoclonal vs Polyclonal Reagents.

OBJECTIVES: Free light chain (FLC) measurement gained a lot of interest for diagnostic workup of monoclonal gammopathy. METHODS: We evaluated the performance of turbidimetric polyclonal Freelite (The Binding Site, Birmingham, UK) assays on Cobas 6000 (Roche Diagnostics, Rotkreuz, Switzerland) and nephelometric monoclonal N Latex (Siemens Healthcare Diagnostics, Marburg, Germany) assays on BN ProSpec (Dade Behring, Deerfield, IL) vs established nephelometric Freelite assays on BN ProSpec. RESULTS: Analytical performance was acceptable. Method comparison (n = 118) showed significant proportional FLC differences for N Latex assays. However, good correlation and clinical concordance were shown. Recovery study in the low concentration range demonstrated consistent over- and underrecovery for Freelite reagents, hampering future research on prognostic value of suppressed noninvolved FLC. Antigen excess detection was successful for κ FLC in three-fourths of cases with Freelite reagents and in all cases with N Latex reagents. However, the latter resulted in underestimated κ FLC concentrations. CONCLUSIONS: FLC analysis requires continuous awareness of analytical limitations. Monitoring of disease response requires FLC analysis on the same platform using the same reagents.

Analytical and diagnostic performance of two automated fecal calprotectin immunoassays for detection of inflammatory bowel disease.

BACKGROUND: We evaluated the (pre-)analytical and diagnostic performance of two automated fecal calprotectin (FC) immunoassays, Liaison® Calprotectin (Diasorin) on Liaison® XL and fCAL™ turbo (Bühlmann laboratories AG) on Cobas C501 (Roche Diagnostics), and compared it with our established Bühlmann ELISA method. METHODS: Our study comprised 229 consecutive patients with clinical suspicion of inflammatory bowel disease (IBD). RESULTS: All assay related stool extraction procedures showed excellent correlation with the established method, but the new stool extraction devices tend to give higher results as compared with stool weight methods. Both automated assays demonstrated good performance in terms of precision (CVt≤8.1%), accuracy (bias≤6.7%) and total error (≤16.4%). Method comparison with established enzyme linked immunosorbent assay (ELISA) showed good correlation (rs>0.925), but regression analysis showed significant proportional differences. Diagnostic performance characteristics with regard to diagnosis of IBD were good and in line with other reports. In addition, we were able to show that optimization of manufacturer's cut-off and moreover, the introduction of a gray zone resulted in a significant increase of post-test probability. CONCLUSIONS: In conclusion, the newly developed stool extraction device protocols showed acceptable and comparable performance to the stool weight method. Overall, the automated Liaison® Calprotectin and fCAL™ turbo assay showed good analytical and diagnostic performance for detection of IBD.