In addition, the evidence for its accuracy in COVID-19 diagnosis relies on manufacturers’ self-validation and on the literature available, which offer estimations in selected biased populations resulting from laboratory testing data sets, or subgroups of patients. However, the usefulness and accuracy of RDT for antibody detection has been widely questioned, due to their general lack of quantitative data, limited sensitivity and specificity when compared to non-RDT methods. Unlike serological tests, RDT for anti-SARS-CoV2 antibodies have the advantage of being simple to run and interpret and can be used at point of care (POC) as an alternative to diagnostic serology facilities. The most common current diagnostic platforms utilised for SARS-CoV-2 specific antibody detection comprise rapid diagnostic tests (RDTs) with a qualitative (or semi-quantitative) assessment of antibodies mainly based on lateral flow assays (LFA) and centralised quantitative serological laboratory testing. In addition, SARS-CoV-2 specific antibody detection is considered to complement NAAT, particularly in the late stages of disease (3–4 weeks post-symptom onset) to identify prior or late infection for clinical and epidemiological purposes. The performance of nucleic acid amplification test (NAAT) in respiratory samples is currently the gold standard for confirming diagnosis, while rapid SARS-CoV-2 antigen diagnostic tests are used as an alternative to NAAT, with typically lower sensitivity than NAAT. Since the beginning of the pandemic, market was flooded with several coronavirus disease 2019 (COVID-19) diagnostic tests of different classes with variable testing validation and regulatory oversight. The RDT used in our study can be a non-invasive and reliable alternative to serological tests and facilitate both qualitative and a semi-quantitative antibody detection in COVID-19.Īccess to accurate and timely diagnostic test for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection plays a major role to optimise clinical care and public health management worldwide. RDT compared to the NAAT gold standard in 858 patients showed 78.5% sensitivity (95% CI 75.1%-81.7%) and 94.1% specificity (95% CI 90.4%-96.8%), with variable accordance depending on the timing from symptom onset. In patients with a diagnosis of COVID-19, accordance between LFA and CLIA was maintained as a function of time from the onset of COVID-19 disease and the severity of disease both for qualitative and semi-quantitative assessments. The qualitative and semiquantitative agreement analysis performed in the whole sample between LFA and CLIA provided a Kendall’s tau of 0.578 (p < 0.001) and of 0.623 (p < 0.001), respectively, for IgM and IgG. Overall, 720 paired antibody measures were performed on 858 patients. Interpretation of RDT was qualitative (positive/negative) and semi-quantitative based on a chromatographic intensity scale (negative, weak positive, positive). SARS-CoV-2 antibodies were simultaneously measured with lateral flow immunochromatographic assays (LFA), the Cellex qSARS-CoV-2 IgG/IgM Rapid Test (by capillary blood), the iFlash-SARS-CoV-2 IgG/IgM chemiluminescent immunoassay (CLIA) (by venous blood) and the nucleic acid amplification test (NAAT) in samples from in- and out-patients with confirmed, suspected and negative diagnosis of coronavirus disease 2019 (COVID-19) attending Udine Hospital (Italy) (March-May 2020). Therefore, the objective of the study was (a) to compare the efficacy of SARS-CoV-2 antibody detection between RDT and laboratory serology, trying to identify appropriate semi-quantitative cut-offs for RDT in relation with quantitative serology values and to (b) evaluate diagnostic accuracy of RDT compared to the NAAT gold standard in an unselected adult population. There is limited information to compare the qualitative and semi-quantitative performance of rapid diagnostic tests (RDT) and serology for the assessment of antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
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