Thorax computed tomography findings and anti-SARS-CoV-2 immunoglobulin G levels in polymerase chain reaction-negative probable COVID-19 cases

Abstract

OBJECTIVE: This study aimed to evaluate the SARS-CoV-2 immunoglobulin G (IgG) levels after 6 months of polymerase chain reaction (PCR) negative but assumed to be COVID-19 positive cases to investigate the relationship between IgG levels and thoracic computed tomography (CT) findings. METHODS: This was a single-center study that included patients whose PCR test results were negative at least three times using nasopharyngeal swabs but had clinical findings of COVID-19 and thoracic CT findings compatible with viral pneumonia. Six months after discharge, the IgG antibodies were analyzed. The cutoff value for negative and positive serology was defined as <1.4 (index S/C) and ≥1.4 (index S/C), respectively. In addition, the patients were categorized according to their thoracic CT findings as high (typical) and low (atypical). Also, the patients were grouped into classes as <5% lung involvement versus ≥5% lung involvement. RESULTS: The patients' mean age was 49.78±12.96 years. PCR was negative, but patients with COVID-19 symptoms who had SARS-CoV-2 IgG positive were 81.9% (n=95). The antibody titer and lung involvement ≥5% were statistically significantly higher in SARS-CoV-2 IgG positive cases (p<0.001 and p=0.021). Age and chest CT findings were the risk factors for lung involvement (OR=1. 08, p<0.001 and OR=2.19, p=0.010, respectively). CONCLUSION: This study is valuable because increasing severity (≥5%) of lung involvement appears to be associated with high and persistent IgG antibody titers. In probable cases of COVID-19, even if the PCR test is negative, high IgG titers 6 months after discharge can predict the rate of lung parenchymal involvement.

An update on lateral flow immunoassay for the rapid detection of SARS-CoV-2 antibodies

“…In one study on 320 patients with confirmed COVID-19, the rate of chest computed tomography (CT) findings was significantly higher in patients with antibody positivity than in those with antibody negativity [88] . This was confirmed by another study showing that increasing severity of lung involvement is associated with high and persistent IgG antibody titers [89] . It is noteworthy that studies correlating more severe disease to more vigorous antibody response in COVID-19, are performed using laboratory tests, and not LFIAs, to assess the antibody titer [90] .…”

“…Theoretically, LFIA should be superior to laboratory tests for large-scale evaluation of vaccine effectiveness due to lower costs and detection time [113] . However, although those LFIAs using the protein pair RBD/ACE2 can perform accurately for certain applications, in practice a number of problems have risen up in the use of rapid tests in post-vaccination [89] , [90] . No doubt that an association exists between the efficacy of the vaccine and neutralizing antibody titers, but comparison of immune responses provided by different vaccines is challenging and different approaches have been used by vaccines developers [117] , [118] .…”