Given the exceptional situation in which this pandemic is developing, the evaluation of the assays has been limited by their availability, as the development and commercialization of specific reagents for SARS-CoV-2 has not been simultaneous. It has been considered a priority to use the same serum when evaluating all the assays, since, in our opinion, this increases the validity of the results obtained. For this reason it was necessary to preserve the serum extracted from patients. In our case it was frozen, being defrosted with each assay examined. Due to the high number of them to be evaluated, this freezing and thawing process was carried out more than what, in our opinion, is desirable. We believe that this may limit the quality of the results obtained. The results are summarized in Table 1.
- Immunochromatography Lateral Flow type:
Wondfo® SARS-CoV-2 Antibody: Total antibody sensitivity was 76%, with a specificity of 100%, PPV of 100% and NPV: 81%.
SGTi-flex® COVID-19 IgM / IgG, which separates the two antibodies: in the case of IgG, a sensitivity of 40%, specificity of 100%, PPV: 100%, NPV: 62.5% was obtained. For IgM, sensitivity 70%, specificity 90%, PPV: 87.5%, NPV: 75%. If we consider an Ig of the two positive (IgG or IgM), the sensitivity rises to 74%, the specificity to 90%, PPV of 88.1% and NPV of 77.6%.
Innovita® 2019 n-CoV Ab Test Colloidal Gold also discriminates between the two antibodies. The results obtained for IgG were: sensitivity of 44%, specificity of 98%, PPV: 95.7%, NPV: 63.6%. The results obtained for IgM were: sensitivity: 52%, specificity: 100%, PPV: 100%, NPV: 67.6%. The results obtained for IgG or IgM, considering one of the two Ig positive, were as follows: sensitivity: 58%, specificity: 98%, PPV: 96.7%, NPV: 70%.
VIRCLIA IgG Monotest Vircell®: sensitivity of 48%, specificity of 96%, PPV: 92%, NPV: 65%.
VIRCLIA IgM+A Monotest Vircell®: sensitivity 63%, specificity 96%, PPV: 94%, NPV: 72%. If we consider a sample as positive if it has IgG and/or IgM+A, the results were as follows: 65% sensitivity, 94% specificity, PPV: 91%, NPV: 73%.
SARS CoV-2 IgG Architect Abbott®: It should be noted that, despite not being advised by the manufacturer, the technique was tested with discomplementated serum because it was the last assay to be available and previously the serum had been discomplemented as it was an essential requirement to analyze Vircell's ELISA and CLIA techniques. The results obtained for IgG were a sensitivity of 52%, specificity of 100%, PPV: 100%, NPV: 68%.
COVID-19 ELISA IgG Vircell®: 65% sensitivity, 96% specificity, PPV: 94% and NPV: 73%.
COVID-19 ELISA IgM+A Vircell®: sensitivity 77%, specificity 83%, PPV: 82%, NPV: 78%. If we consider a sample as positive if it has ELISA IgG and/or IgM+A, the results were as follows: sensitivity: 81%, specificity: 81%, PPV: 81%, NPV: 81%.
EUROIMMUN® ELISA Anti SARS-Co-V2 IgG: sensitivity of 37.8%, specificity of 100%, PPV: 100%, NPV: 61.6%.
EUROIMMUN® ELISA Anti SARS-Co-V2 IgA: a fail dispensing the stopping solution during the performance of Negative Controls group, caused the invalidation of the assay. Therefore, only sensitivity data are presented for this antibody (IgA) and the IgG+IgA group. The sensitivity for IgA was 88.9%. If we consider a sample as positive if it has an ELISA IgG and/or IgA, as in the previous cases, it should be noted that only Positive Controls have been taken into account because Negative Controls we do not have IgA. In this case, the sensitivity is 88.9%. The IgA and IgG+IgA sensitivity results coincide because there is no patient who has positive IgG and negative IgA.