SARS-CoV-2 testing at R.E.D. Laboratories
R.E.D. Laboratories has been actively engaged in assessing the best testing solutions to provide to its customers, knowing that first-line testing by nucleic acid isolation and amplification is managed by University hospitals and their associated laboratories.
We propose to you 2 types of serology testing: (these tests cannot be used for travel that requires RT-PCR test)
Both are CE-IVD and from well-known European providers.
Please contact us if you are interested in these tests. A specific request form is available on our website. The rapid test can be done on any type of blood sample, thus if you are already sending an EDTA or serum sample for any of our other tests, we can make use of the same sample. The ELISA test requires a serum sample. Please read below for more information about these tests.
Relevance of serological tests
Direct pathogen detection by nucleic acid amplification is the method of choice for detection of acute COVID-19 infections. However, when the adaptive immune response has started and therefore, the viral load is decreasing, the sensitivity of the direct detection decreases correspondingly. After approx. 10-14 days, the pathogen is no longer reliably detectable (Liu et al. 2020), which is why serological procedures can be applied from this phase on. The following areas of application have been described for serology:
● Tracing of infection chains to identify persisting or past infections and to allow taking the appropriate measures. (source: European Centres for Disease Control and Prevention (ECDC) – Technical Report – Novel coronavirus [SARS-CoV-2])
● Tracing of potentially immunized persons that didn’t develop any symptom, contributing thus to distinguishing from the persons still at risk
● Decision aid at the moment of releasing patients from medical care (source: European Centres for Disease Control and Prevention (ECDC) – Technical Report – Novel coronavirus [SARS-CoV-2])
● Identification of pathogen contact or a past infection with SARS-COV-2 (source: Bao et al., Reinfection could not occur in SARS-CoV-2 infected rhesus macaques, bioRxiv 2020.03.13.990226 and Okba et al., SARS-CoV-2 specific antibody responses in COVID-19 patients, medRxiv 10.1101/2020.03.18.20038059).
● Epidemiological studies in the population (source: Robert-Koch Institute [RKI] – SARS-CoV-2 / Characteristics of coronavirus disease 2019 [COVID-19])
SEROLOGY RAPID TEST (IgG/IgM)
The serology rapid test is not a first-line diagnostic tool for uncovering patients with an active Covid-19 disease. It is a point-of-care professional use only tool for a rapid detection of immunized patients.
The rapid test proposed by R.E.D. Laboratories is CE-IVD and has obtained all necessary regulatory authorizations. The rapid test has been tested in a hospital setting by doctor Dieter Desmet, lab director at the hospital AZ Delta, who does clinical validation of the rapid test there, together with Prof. Geert Martens. Their observations for this test are that it is a useful test, but needs to be interpreted carefully, taking into account the importance of disease severity, disease onset time and immune status of the patient:
Patients that are very ill (hospitalised, cytokine storm, humoral response) will have an immediate positive test. Patients with milder disease courses (at home, late hospitalisation) will take up to 21 days after onset of symptoms to have IgG antibodies detectable by a rapid-type test and only then they will test positive. Severely immune deficient patients can test negative and remain negative. This is similar to other serologies.
Doctor Dieter Desmet said the IgG results of the rapid tests are trustworthy, while the IgM results have many false positives and negatives, just like other serology tests. In line with this, he emphasised that this type of test is not a first-line diagnostic, but an analytical test that can only detect past infections or explosive current infections, given that the lab or doctor is very aware of the importance of the onset time and the severity of the symptoms and the immune status of the patient for interpretation of the test results. And that they be willing to re-test after 21 days if necessary (when no exact symptom onset is known, or when testing an asymptomatic patient). It is expected that acquired immunity would protect the patient for 6-12 months because severe re-infections have not been detected so far (except in people that are immune deficient).
The sensitivity of IgM test is 87,9% (87/99) and specificity is 100% (14/14) compare to the RT-PCR.
The sensitivity of IgG test is 97,2% (35/36) during the convalescence period, and specificity is 100% (14/14).
anti-SARS-CoV-2 ELISA tests
The anti-SARS-CoV-2 ELISA tests proposed by R.E.D. Laboratories are fully developed and manufactured by EUROIMMUN AG (Lübeck, Germany). In attachment you can find the article by Okba et al. The authors describe the serological response of a SARS-CoV-2 infection and the performance of the anti-SARS-CoV-2 ELISA’s of EUROIMMUN AG compared to reference tests such as PRNT (Plaque Reduction Neutralization Test) in well-defined cohorts. (https://www.medrxiv.org/content/10.1101/2020.03.18.20038059v1)
We would like to synthesize the main conclusions of the authors for you: S1 is more specific than N or S (complete) protein as an antigen for SARS-CoV-2 serological diagnosis.
● EUROIMMUN Anti-SARS-CoV-2 ELISAs (IgA and IgG) show 89-100 % sensitivity.
● The specificity of the EUROIMMUN Anti-SARS-CoV-2 ELISAs varies between 87.5 – 95.5 % for IgA and 83.5 – 97.5 % for IgG, depending on the used sample panel.
● EUROIMMUN Anti-SARS-CoV-2 ELISAs (IgA and IgG) correlate strongly with PRNT.
● The detection of IgA antibodies can have an added value in diagnosing SARS-CoV-2 infection at the early phase of the disease.
Both test systems are therefore not only ideal for supporting the diagnosis of SARS-CoV-2 infection, but also for differentiating from infections with other pathogens causing similar symptoms.
IMPORTANT NOTE: The results presented in this study were based on EUROIMMUN Anti-SARS-CoV-2 ELISAs (IgA and IgG) available for research use only purposes. EUROIMMUN was actively taking part in this study and had access to the results before this publication. Based on the collected data, EUROIMMUN performed a redesign on the IgG Kits, leading to an improved signal-to-noise ratio. This improved version of the EUROIMMUN Anti-SARS-CoV-2 ELISA (IgG) underwent the complete CE registration process. All CE marked lots are produced after the redesign.
Relevance of IgA testing
The Anti-SARS-CoV-2 ELISA (IgA) was designed in order to reduce or even close the diagnostic gap between direct detection and serology. According to MiQ (Mikrobiologisch-infektiologischer Qualitätsstandard), secretory antibodies of class IgA are an “essential carrier of the humoral immune response in the areas of mucous membranes and bodily fluids”. Therefore, their detection has a diagnostic relevance for supporting diagnostics in suspected cases of respiratory infection. Like the IgG test, the Anti-SARS-CoV-2 ELISA (IgA) is based on recombinant S1 structural protein and hence enables a significantly more specific detection than would be possible by determination of IgM antibodies, which are mainly directed against the highly conserved (N)-protein. Using the Anti-SARS-CoV-2 ELISA (IgA), the risk of detection of cross-reactive antibodies against other coronaviruses is significantly lower in comparison to IgM detection.
