QuantiFERON SARS-CoV-2

The QuantiFERON SARS-CoV-2 assay is 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. The amount of IFN-γ produced is measured using enzyme-linked immunosorbent assay (ELISA).

The QuantiFERON SARS-CoV-2 assay is intended to aid in assessing cell-mediated immune (CMI) response in individuals without a history of SARS-CoV-2 infection and who have received COVID-19 vaccination using vaccines targeting the viral spike (S) protein of the SARS-CoV-2 virus.

The QuantiFERON SARS-CoV-2 assay should be used in conjunction with other laboratory testing and epidemiological/clinical evaluation to assess an individual’s immune response due to COVID-19 vaccination.
It may take several days after vaccination to develop T cell immune responses, although the duration of time that T cell immune responses are present is not well characterized in vaccinated individuals.

Non-reactive results do not preclude active SARS-CoV-2 infection or determine the effectiveness of COVID-19 vaccines. If active infection is suspected, confirm by using another molecular or antigen test for SARS-CoV-2. The results from the assay should always be used in combination with clinical examination, patient medical history, and other findings.

For in vitro diagnostic use.

The clinical performance of the QFN SARS assay was evaluated in a prospective, observational study conducted from June to October 2021 using subjects without a history of SARS-CoV-2 infection and who have received COVID-19 vaccination with vaccines targeting the viral S protein of SARS-CoV-2, as well as those without a history of SARS-CoV-2 infection and who have not received COVID-19 vaccination.

None of subjects were transplant recipients (solid organ or cell) and/or on any treatment for cancer at the time of study participation. 

There were a total of 214 evaluable samples from unvaccinated individuals (Group 1) and 171 evaluable samples from vaccinated individuals (Group 2). For a complete breakdown of study participants, consult the QuantiFERON SARS-CoV-2 ELISA Kit Instructions for Use.

Specificity

The negative percent agreement (NPA) (specificity) was calculated for unvaccinated subjects (Group 1), along with the two-sided 95% exact confidence interval (CI), and is presented in Table 1.

Table 1. Negative Percent Agreement (Specificity)

Sensitivity

The positive percent agreement (PPA) (sensitivity) was calculated for vaccinated subjects (Group 2), along with the two-sided 95% exact CI, and is presented in Table 2.

Table 2. Positive Percent Agreement (Sensitivity)

Positive Percent Agreement by Age

For vaccinated subjects (Group 2), positive percent agreement was stratified by age < 60 and ≥ 60 years and is presented in Table 3.

Table 3. Positive Percent Agreement by < 60 and ≥ 60 Years of Age.

Positive Percent Agreement by COVID-19 Vaccine

For vaccinated subjects (Group 2), positive percent agreement was stratified by COVID-19 vaccine received and is presented in Table 4.

Table 4. Positive Percent Agreement by COVID-19 Vaccine

QuantiFERON SARS-CoV-2 (QFN SARS) is a qualitative assay that uses specialized blood collection tubes, containing peptide antigens that stimulate immune cells using SARS CoV-2 specific proteins. Incubation of the blood occurs in the tubes for 16 to 24 hours, after which, plasma is harvested and tested for the presence of IFN-γ produced in response to the peptide antigens. 

First, whole blood is collected into each of the QuantiFERON SARS-CoV-2 Blood Collection Tubes, which include a Nil tube, Ag1 tube, Ag2 tube, and a Mitogen tube. Alternatively, blood may be collected in a single blood collection tube that contains lithium or sodium heparin as the anticoagulant, and then transferred to QuantiFERON SARS-CoV-2 Blood Collection Tubes.

The QuantiFERON SARS-CoV-2 Blood Collection Tubes are shaken to mix antigen with the blood and should be incubated at 37°C ± 1°C as soon as possible, and within 16 hours of collection. Following a 16 to 24 hour incubation period, the tubes are centrifuged, the plasma is processed, and the amount of IFN-γ (IU/ml) is measured by ELISA. The QuantiFERON SARS-CoV-2 ELISA uses a recombinant human IFN-γ standard, which has been assayed against a reference IFN-γ preparation (NIH Ref: Gxg01-902-535). Results for test samples are reported in International Units per ml (IU/ml) relative to a standard curve prepared by testing dilutions of the standard supplied with the kit.

The plasma sample from the Mitogen tube serves as an IFN-γ positive control for each specimen tested. The Nil tube adjusts for background (e.g., elevated levels of circulating IFN-γ or presence of heterophile antibodies). The IFN-γ level of the Nil tube is subtracted from the IFN-γ level for the Ag1, Ag2, and Mitogen tubes.