Background A Treat-to-Target (T2T) strategy for inflammatory arthritis, targeting remission or minimal disease activity, is the recommended treatment approach by EULAR and ACR. This strategy relies on “tight monitoring” which necessitates regular clinical examination and measuring acute-phase reactants such as C-reactive protein. Calprotectin (MRP8/14; S100A8/A9), a relatively novel inflammation and disease activity marker in the arthritis field, exhibits several features which fit the “theranostic needs” for accurate therapy monitoring. Those features include discrimination between responders and non-responders , detection of subclinical disease activity  and prediction of relapse or radiographic progression . The classical method to determine calprotectin in serum (sCAL) is ELISA which is used in service or central laboratories. A rapid and simple determination of sCAL at the point of care is a substantial step forward in supporting clinicians to deliver an efficient T2T strategy. Here, we report on the validation of a quantitative, rapid test which can measure sCAL within 15 minutes.
Objectives (1) To demonstrate the performance evaluation of a quantitative lateral flow assay combined with a dedicated test reading device for the rapid quantification of calprotectin in serum; and (2) to compare results to a well-established laboratory reference method using patient samples.
Methods The Quantum Blue® sCAL sandwich lateral flow immunoassay uses two highly specific monoclonal antibodies immobilized on the test membrane and on the gold label. 10μL of serum was diluted in 90μL of chase buffer, 60μL of this mixture was applied onto the lateral flow test cassette, which was incubated for 12 minutes at ambient temperature and then measured with the BÜHLMANN Quantum Blue® Reader. Performance evaluation (sensitivity, linearity, high-dose hook effect, interferences) was carried out according to CLSI guidelines. A method comparison based on 178 serum samples from RA and PsA patients was performed against the BÜHLMANN sCAL (MRP8/14) reference ELISA.
Results The linearity study over the complete measuring range together with the observed limit of quantification (LoQ) of <0.5 μg/mL allowed a quantitative measurement in the clinically relevant range from 0.5 to 10.0 μg/mL calprotectin. No high dose hook effect was observed up to a concentration of 200 μg/mL. Moreover, no interferences were detected with triglycerides (37mmol/L), conjugated bilirubin (342μmol/L), unconjugated bilirubin (342μmol/L), and hemoglobin (200mg/dL). The Quantum Blue® sCAL lateral flow assay showed an excellent linear correlation (r=0.94, slope=1.05) to the BÜHLMANN sCAL (MRP8/14) reference ELISA. There was a negligible bias of -3.1% by Bland-Altman difference plot between the sCAL lateral flow assay and ELISA.
Conclusions Rapid quantification of serum calprotectin using the Quantum Blue® sCAL assay represents a fast and reliable method for the determination of inflammation and the disease activity of a patient with inflammatory arthritis at the point of care. This rapid test shows excellent agreement to a corresponding laboratory reference method.
Anink J. Arthritis Res Ther (2015);15:200.
Inciarte-Mundo J. Arthritis Res Ther (2016);18:160.
Hurnakova J. Arthritis Res Ther (2015);17:252.
Disclosure of Interest N. Ryter Employee of: Employee of BÜHLMANN Laboratories AG, A. Szentpetery: None declared, S. Pennington: None declared, R. Cotti Employee of: Employee of BÜHLMANN Laboratories AG, O. FitzGerald: None declared, J. Weber Employee of: Employee of BÜHLMANN Laboratories AG