Elecsys anti sars cov 2 eclia assay

The Elecsys^® Anti-SARS-CoV-2 ECLIA assay (Roche Diagnostics AG, Rotkreuz, Switzerland) performed on the cobas e 801 analyzer (Roche Diagnostics) was used. This is a high-throughput assay with an estimated TAT of 20 min per sample. The assay is CE marked and at the beginning of May 2020, received the Food and Drug Administration's EUA. Results [in cut-off index (COI)] are determined automatically by the analyzer's software that compares the electrochemiluminescence signal obtained from the reaction product of the serum/plasma sample with the signal of the cut-off value previously obtained by calibration. The cut-off value for reactivity (positivity) is equal to 1.0 COI. The assay uses a recombinant protein representing the nucleocapsid antigen, and its format favors the preferential detection of late, mature, and high affinity antibodies. Therefore, despite that this assay detects all classes of immunoglobulin (IgA, IgM, and IgG), it detects predominantly IgG (10 (link)).

Total levels of anti-SARS-CoV-2 spike antigen antibodies (predominantly IgG) (S-RBD) were measured using the FDA approved Elecsys^® Anti-SARS-CoV-2 ECLIA assay Roche Diagnostics EG on the cobas e 801 analyzer (27 ). Manufacturer recommendations for evaluation of results were implemented by including 3 different cut-off values to accurately stratify patients into the following subgroups: negative (<0.8 U/mL); inconclusive (0.8 to <5 U/mL); and positive (≥5 U/mL).
Results for anti-N antibodies were expressed as “present” or “absent”, on the basis of a cut-off index (COI) ≥1.0 and <1.0, respectively.
SARS-CoV-2 CMI response was assessed by the IGRA (Interferon-Gamma Release Assays) QuantiFERON Human IFN-gamma SARS-CoV-2, Qiagen^® (QFN SARS) assay, an in vitro diagnostic test designed for the qualitative detection of interferon-γ (IFN-γ), produced by CD4+ and CD8+ T cells, in response to stimulation by a SARS-CoV-2 peptide cocktail in heparinized whole blood. Details about the performance and interpretation of the IGRA assay are provided in the supplementary materials and Table 1S.

Antibody positivity was determined by Elecsys^® Anti-SARS-CoV2 ECLIA assay (Roche Diagnostics AG, Rotkreuz, Switzerland) and defined according to the receptor-binding domain (RBD) IgG titer. Minimum and maximum thresholds for the detection of anti-RBD antibody levels were 0.4 and 2500 UI/mL, respectively. A positive antibody response was defined as an anti-RBD titer ≥5 U/mL, as previously specified [9 (link)].
Patients were encouraged to undergo antibody testing after the third dose (after at least two months). The third dose was recommended to all patients, regardless of the levels of antibodies before its administration, when available, following the indications of the National Ministry of Health.