Performance of Commercially Antibody-based assays for Covid-19 Detection

The ongoing SARS-CoV-2 pandemic caused by novel coronavirus has become a threat to international public health. To tackle this pandemic reliable and rapid immunodiagnostic strategies are required. This study will briefly review the antibody diagnosis methods and recent clinical studies in this regard. The sensitivity and specificity after two weeks are considered to examine the late stages response of the disease. Among current studies on serology testing, 27 recent publications used commercial assays to diagnose IgM and IgG against SARS-CoV2 are discussed in this paper. A total of 54 kit-testing for antibodies, 20 are based on ELISA principles using serum or plasma samples with a sensitivity range of 55.6 % and 100% for IgG and between 77.3 % and 82.7 % for IgM. The specificity for both IgG and IgM ranges between 87.5 % to 100%. Twenty-seven kits are using lateral flow platforms and thirteen kits using luminescent immunoassays, including ten chemiluminescence immunoassay (CLIA) with sensitivity between 64 % and 97% for both IgM and IgG and 75.6% to 100% for IgG. The specificity is reported between 85% to 100% and 90.9 to 100%, respectively. Two Electrochemiluminescence Immunoassay (ECLIA) also showed high sensitivity and specificity for both antibodies. Antibody-based serology testing for SARS CoV-2 would be clinically important as a determination to return to work in society. Currently focusing on healthcare workers would be critical; however, there will be a significant need for serology-based testing to enable individuals to return to work or school safely in the overcoming months. and their actual sensitivity and specificity are not fully understood.


Introduction
The diagnosis of COVID-19 is mainly based on the polymerasechain-reaction (PCR) assay. Although PCR is high in sensitivity, there is a possibility of false-negative results. Numerous diagnosis immunoassays are developed to test COVID-19, including fluorescence assays, chemiluminescence immunoassays (CLIAs), enzyme-linked immunosorbent assays (ELISA), rapid antibody immunochromatographic test, and point-of-care test (POCT).
Although there is a variation among test methods, they are mainly testing for the presence of two types of blood antibody, IgM and IgG or both. However, the timeline varies, and people respond differently to infection; these tests might detect antibodies by two or three weeks after symptom onset. These tests are not meant generally to active diagnosis infection but are able to identify prior infection. Many of these testing assays have not been validated yet, and their actual sensitivity and specificity are not fully understood.
Research Register and In Process were searched applying the search terms "COVID-19", "SARS-CoV-2", "antibody testing", and "serological test", from December 2019 to June 2020. The studies using non-commercial kits and the ones which performed serology tests for less than two weeks have been excluded from this review.

Data extraction
From each publication, the following data were extracted: first author's last name, year of publication, the study name, follow up time, number of positive cases, number of control case, sensitivity and specificity of the kit for each Ig protein, method of testing and the kits manufacture company, country where the study was conducted.

Diagnosis of COVID-19
Immunological and serological assays  Indirect ELISA: A secondary antibody binds to the primary antibody to interact with the substrate. Sandwich ELISA: wells are coated with the capture antibody, the antigen will be incubated between capture antibody ant primary antibody, an enzyme-conjugated secondary antibody binds to this complex.

Lateral flow assay
In a lateral flow assay, the sample is added to the sample application pad at one end of the strip. The sample then migrates to the conjugate release pad, where a detection particle that has been conjugated to a biological component of the assay is held.
The sample and the detection reagent migrate to the reaction membrane, where a second biological component of the assay has been immobilized in a test line. The detection reagent binds of the control further along the membrane to indicate that the assay has run successfully. The analysis is either captured at the test line or continues to migrate until it reaches the absorbent wicking pad at the end of the strip (Figure 2) [1].

Luminescent analytical system
The luminescent immunoassay is a technique capable of identifying specific antigenic molecules in the sample fluid, using the antibody and antigen labeled by an enzyme. There are several types of luminescent immunoassay, including chemiluminescent analytical system (CLIA) and electrochemiluminescence Immunoassay (ECLIA). In ECLIA, the species emit light as a result of electron transfer reaction generated by electrodes, while in CLIA, the light is the product of the chemical reaction.

Plaque-reduction neutralization assay
The presence of infection can also be detected using the plaque assay. Indicator cells that are permissive to infection are needed to perform the test. Sample contain viruses are added to previously

Result and Discussion
In total, 27 studies including 2183 previously confirmed patient for COVID 19 were included in this review. Serological assays with the goal of finding IgM and IgG proteins are most effective within the few days after the onset of initial symptoms, and they are not advised as an acute phase diagnostic method. Several medical provisioner companies, scientific and research centers, have made great effort to develop the best diagnosis assays. A summary of recent studies using several commercial assays is presented in assays and they reported diagnostic sensitivities and specificities above 93.8% and 85.9%, respectively for all CLIA assays [7].

Conclusion
As SARS-CoV-2 progresses over time, and the virus will be cleared from the immune system, it becomes more difficult to detect the viral RNA and viral protein using RT-PCR. However, the specific antibody produced against SARS-CoV-2 by the immune system can be detected using immunoassays. Reliable immunoassays tests can identify individuals who have already been infected and may not have been diagnosed at the time. The positive antibody test suggests that individuals may have gained immunity, or reinfection may not be as severe as the primary one. Identifying individuals who have already had infection is more important from a population health perspective than an individual's health prepositive. These individuals may help to identify the priority for vaccination or may be able to donate blood to critically sick patients who are fighting infection. During the pandemic COVID-19 reliable diagnostic test that targets both infected and recovered patients are needed to help combat the virus.