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.

Analytical performance and diagnostic accuracy of six different faecal calprotectin assays in inflammatory bowel disease.

BACKGROUND: We evaluated the analytical performance of six different faecal calprotectin immunoassays together with their diagnostic accuracy in the discrimination between functional and organic bowel disorders. METHODS: The faecal samples were obtained from inflammatory bowel disease patients (n=27) at the time of diagnosis [Crohn's disease (n=15), colitis ulcerosa (n=12)], gastroenterologic disease control patients (n=52) and rheumatologic disease control patients (n=26). All individuals included in the study underwent a concurrent ileocolonoscopy. Analytical performance (imprecision, accuracy, carry-over, correlation and agreement) and diagnostic accuracy (sensitivity, specificity, likelihood ratios) of the different assays were evaluated. RESULTS: All methods demonstrated good analytical performance, but within-run and total imprecision varied depending on the assay methodology used. Using Passing Bablok and Bland-Altman analyses, low quantitative agreement was observed between the assays. All assays showed excellent diagnostic accuracy, with areas under the receiver operating characteristic curves (ROC) ranging from 0.974 to 0.998. The AUCs were not significantly different between assays (p>0.05). Diagnostic sensitivity at the cut-off at a fixed specificity of 75% ranged from 95.2% to 100%. Introduction of multiple result intervals increased the clinical interpretation of all the assays. CONCLUSIONS: Analytical and diagnostic performance of the evaluated faecal calprotectin assays is good, but numerical values differ substantially between the assays necessitating the use of different clinical cut-offs. Introduction of multiple result intervals aids in clinical decision-making.

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.

Comparison of two immunoassays for measurement of faecal calprotectin in detection of inflammatory bowel disease: (pre)-analytical and diagnostic performance characteristics.

BACKGROUND: Symptoms of inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS) can overlap. Faecal calprotectin has recently been established to be a non-invasive marker for neutrophilic intestinal inflammation. We compared two devices for extraction of faecal calprotectin. Based on these results, two immunoassays for measurement of faecal calprotectin were evaluated. METHODS: Samples were extracted using the Thermo Fisher extraction device (Thermo Fisher Scientific) and Smart Pep extraction device (Roche Diagnostics) and measured with the EliA Calprotectin immunoassay (Thermo Fisher Scientific) on ImmunoCAP 250. The performance of both assays was investigated by enrolling 183 consecutive patients (79 males, 104 females; median age 32 years) with clinical suspicion of IBD. Faecal calprotectin was measured using a recently launched immunoassay, EliA Calprotectin in comparison with an established immunochomatographic point-of-care-test (POCT, Quantum Blue Calprotectin; Bühlmann). Results were compared with endoscopic and histological findings. RESULTS: The use of the Thermo Fisher extraction device resulted in an underestimation of faecal calprotectin concentrations, especially in liquid stool samples. IBD was diagnosed in 51/183 patients (27.9%) [Crohn's disease (CD, n=37), ulcerative colitis (UC, n=14)]. After adjusting the optimal cut-off for detection of IBD using receiver operating curve analysis, a sensitivity of 94.1% and 90.2% and specificity of 87.9% and 90.9% for the EliA and POCT assay, respectively, were obtained. CONCLUSIONS: The Thermo Fisher device is not reliable for extraction of faecal calprotectin. The performance characteristics of the EliA Calprotectin assay are statistically equivalent to the Bühlmann POCT.

Faecal calprotectin: comparative study of the Quantum Blue rapid test and an established ELISA method.

BACKGROUND: Faecal calprotectin is a non-invasive marker for neutrophilic intestinal inflammation. It can be used in the differential diagnosis between functional and organic bowel disease. Moreover, it correlates with endoscopic organic bowel disease activity. The objective of this study is to evaluate a recently launched quantitative immunochromatographic point-of-care test: Quantum Blue Calprotectin (Bühlmann Laboratories AG, Schönenbuch, Switzerland) in comparison to an established ELISA method (Bühlmann Laboratories AG). METHODS: We included 142 samples, either archived (­80°C) faecal extracts or fresh routine samples. Both the normal range cartridges as well as the high range cartridge from the point-of-care test were used. The ELISA was compared with the point-of-care test and the optimal the point-of-care test cut-off values were searched for using Microsoft® Excel 2002 and MedCalc Software version 10.0.0.0 (Mariakerke, Belgium). RESULTS: In the method comparison a determination coefficient (R2) of 0.89 was found. The Passing Bablok regression analysis showed a significant deviation from linearity (y=­40.8+1.0x). The use of a cut-off value of 30 µg/g faeces and a grey zone of 30­110 µg/g faeces resulted in the best agreement between the ELISA interpretation and the point-of-care test interpretation, with 89.4% (127/142) agreement and 10.6% (15/142) mismatches. CONCLUSIONS: We may conclude that the point-of-care test can serve as a reliable alternative to the time consuming ELISA in the differential diagnosis between functional and organic bowel disease. Furthermore, it seems to be reliable in the follow-up of inflammatory bowel disease patients.

Expert opinion for use of faecal calprotectin in diagnosis and monitoring of inflammatory bowel disease in daily clinical practice.

BACKGROUND: Despite many publications regarding the role of faecal calprotectin (FC) in inflammatory bowel disease (IBD), clear recommendations for its use in clinical practice are currently lacking in the literature. AIM: The aim of this article is to provide practical guidance for clinicians for the use of FC in the detection and management of patients with IBD. METHODS: All relevant publications were analysed and practical statements were proposed based on a Delphi consensus approach. RESULTS: Different commercial assays have been developed but international standardisation is lacking. FC can help in the diagnosis process of IBD. In IBD, FC can predict response to therapy, detect subclinical inflammation and help to drive treatment decisions to achieve better endoscopic and clinical outcomes. After Crohn's surgery FC can identify patients with early endoscopic recurrence. CONCLUSION: Although major therapeutic changes should not be based on FC alone, FC is a valuable tool to optimise the care for IBD patients.

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.

Laryngeal zoster with multiple cranial nerve palsies.

A young immunocompetent patient is presented with a very rare presentation of a common viral illness: herpes zoster of the left hemilarynx with sensorial and motoric neuropathy of three ipsilateral lower cranial nerves: IX, X and XI. The mucosal lesions were discovered during upper gastrointestinal endoscopy. PCR of erosional exsudate confirmed the clinical diagnosis. Antiviral therapy and corticosteroids possibly contributed to the prosperous evolution with complete healing.

Comparison of 6 automated assays for total and free prostate-specific antigen with special reference to their reactivity toward the WHO 96/670 reference preparation.

BACKGROUND: Prostate-specific antigen (PSA) assays have historically produced different results. Our aim was to investigate the comparability of assay results of selected commercially available assay methods designed to measure total, free, or complexed PSA (tPSA, fPSA, and cPSA). METHODS: We measured tPSA, fPSA, and cPSA in 70 samples and in the WHO PSA 96/670 reference preparation with 6 assays (Beckman-Coulter Access, Abbott ARCHITECT and AxSYM, Bayer Advia Centaur, DPC IMMULITE 2000, and Roche Modular Analytics E170). We also calculated the fPSA/tPSA ratio. RESULTS: The mean deviations from the expected tPSA and fPSA values for the WHO 96/670 reference preparation were 0.37 (range, 0.01-1.32) and 0.19 (range, 0.05-0.49) microg/L, respectively. When plotted against the expected WHO 96/670 reference preparation value, regression slopes varied from 0.99 to 1.22 and r2 from 0.9996 to 1.000. When total PSA was measured in mixtures of sera with high and low tPSA concentrations, the mean (SD) slope of regression of different assays against an in-house method was 1.04 (0.09). In these specimens, the fPSA/tPSA ratio was 0.11-0.14 with different methods. The tPSA and fPSA values in patient samples measured in different assays and plotted against ARCHITECT gave regression slopes from 0.88 to 0.97. The results of the studied assays for tPSA in serum samples agreed within 15%, from each other, and all results for the WHO 96/670 reference preparation were within 6.8% (confidence interval, 1.7%-15.2%) of the expected value. The results for fPSA were more diverse. CONCLUSIONS: Differences among PSA assays appear to have decreased since introduction of the WHO 96/670 reference preparation, but further efforts are needed to harmonize fPSA assays.