# Diagnostic Performance of Serological Assays in the Detection of SARS-CoV-2: A Review
## 4 Discussion  
This review aimed to provide an overview of the existing serological tests, assessing their capacity to detect the presence of IgM and IgG antibodies against SARS-CoV-2 in blood samples taken from patients. During SARS-CoV-2 infection, an overactivation of natural immunity cells, such as macrophages and monocytes, has been recorded, which consequently causes the diminution of lymphocytes and the increase of neutrophils, interleukin-6 (IL-6) and reactive protein C (PCR) [42]. With regard to the adaptive immune response, the activation of B lymphocytes of the humoral immunity (which occurs approximately after one week from infection) leads to the production of specific antibodies against SARS-CoV-2: IgM and IgG [43]. According to the literature, IgM antibodies constitute the first line of defense during a viral infection and can indicate the acute phase of the disease; IgG antibodies represent long-term immunity and immunological memory, and their presence highlights that exposure to the pathogen has occurred several days before [43; 44]. The study by [PERSON] et al. [45] tested four different immunomodhtographic assays, demonstrating that the antibodies' detection time was, on average, 8-10 days after the symptoms' onset, while the case report of [PERSON] et al. [46] recorded a progressive increment of anti-SARS-CoV-2 IgM and IgG from day 7 until day 20 from the beginning of the illness. Two of the articles selected for this review reported that the IgM-positive rate tended to increase at first but then declined, while those of IgG were higher than of IgM at all times [34], and that IgM and IgG positive rates increased from 50% to 81% and from 81% to 100%, respectively [41]. [PERSON] et al. [37] divided the infection into three stages: early (1-7 days from the onset), intermediate (8-14 days) and late (more than 15 days), establishing that the positive rate of IgM was raised from 11.1% (early stage) to 78.6% (intermediate stage) and 74.2% (late stage), whereas that of IgG was 3.6% in the early stages and 57.1% and 96.8% in the intermediate and late stages, respectively. [PERSON] et al. [33] was able to detect IgM and IgG from day 10 to day 30 and from day 20 onwards after COVID-19 infection, respectively. On the basis of the results obtained by [PERSON] et al. [35], the persistence of positive real-time RT-PCR seemed to be shorter in symptomatic patients, who developed IgM antibodies. The median seroconversion time detected by [PERSON] et al. [39] was day 12 and day 14 for IgM and IgG respectively. Among the five patients with severe symptoms analyzed by [PERSON] et al. [40], the antibody response was individuated within week 2, and three out of five of these subjects developed IgG response prior to viral clearance, indicating that high levels of this new pathogen viral load may provide an early antibody response [47; 48]. Almost all the included items agreed on the fact that serological tests could be effective and reliable diagnostic tools for SARS-CoV-2 infection identification, since they are able to provide high sensitivity and specificity, and that their utilization should be complementary to the execution of real-time RT-PCR. Because of its several limitations, rRT-PCR could also report negative results in infected individuals: very early or late collection of swabs, poor quality of the specimen containing insufficient material quantity, or wrong technical procedures. Furthermore, it takes a long time to generate RT-PCR test results, it requires first-rate certified laboratory facilities with ad-hoc educated staff, and it may provide different results depending on the sampling site (oropharyngeal or nasopharyngeal swabs) [49]. Antibody assays could provide a faster, less expensive and simpler (no laboratory training need) method to diagnose COVID-19 [38]. As [PERSON] et al.