Improved Detection of Antibodies against SARS-CoV-2 by Microsphere-Based Antibody Assay.

Currently available COVID-19 antibody tests using enzyme immunoassay (EIA) or immunochromatographic assay have variable sensitivity and specificity. Here, we developed and evaluated a novel microsphere-based antibody assay (MBA) for detecting immunoglobulin G (IgG) against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleoprotein (NP) and spike protein receptor binding domain (RBD). The seropositive cutoff value was set using a cohort of 294 anonymous serum specimens collected in 2018. The specificity was assessed using serum specimens collected from organ donors or influenza patients before 2020. Seropositive rate was determined among COVID-19 patients. Time-to-seropositivity and signal-to-cutoff (S/CO) ratio were compared between MBA and EIA. MBA had a specificity of 100% (93/93; 95% confidence interval (CI), 96-100%) for anti-NP IgG, 98.9% (92/93; 95% CI 94.2-100%) for anti-RBD IgG. The MBA seropositive rate for convalescent COVID-19 patients was 89.8% (35/39) for anti-NP IgG and 79.5% (31/39) for anti-RBD IgG. The time-to-seropositivity was shorter with MBA than EIA. MBA could better differentiate between COVID-19 patients and negative controls with higher S/CO ratio for COVID-19 patients, lower S/CO ratio with negative controls and fewer specimens in the equivocal range. MBA is robust, simple and is suitable for clinical microbiology laboratory for the accurate determination of anti-SARS-CoV-2 antibodies for diagnosis, serosurveillance, and vaccine trials.

A comparison between the EQ-5D and the SF-6D in patients with chronic obstructive pulmonary disease (COPD).

BACKGROUND: The appropriate use of generic preference-based measures determines the accuracy of disease assessment and further decision on healthcare policy using quality adjusted life years. The discriminative capacity of different instruments would differ across disease groups. Our study was to examine the difference in utility scores for COPD patients measured by EQ-5D and SF-6D and to assist the choice of a proper instrument in this disease group. METHODS: Differences of mean utility scores of EQ-5D and SF-6D in groups defined by socio-demographic characteristics, comorbidities, health service utilisation and severity of illness were tested using Mann-Whitney test, t-test, Kruskal-Wallis test, Pearson's correlation coefficient and ANOVA, as appropriate. The discriminative properties of the two instruments were compared against indicators of quality of life using receiver operating characteristic curves. The statistical significance of the area under the curves (AUC) was tested by ANOVA and F-statistics used to compare the efficiency with which each instrument discriminated between disease severity groups. RESULTS: Mean utility scores of EQ-5D and SF-6D were 0.644 and 0.629 respectively in the 154 subjects included in the analysis. EQ-5D scores were significantly higher than SF-6D in groups less severe and these differences corresponded to a minimally important difference of greater than 0.03 (p<0.001). EQ-5D and SF-6D scores were strongly correlated across the whole sample (r = 0.677, p<0.001) and in pre-defined groups (r>0.5 and p<0.05 for all correlation coefficients). AUCs were above 0.5 against the indicators of health-related quality of life for both instruments. F-ratios suggested SF-6D was more efficient in discriminating cases of different disease severity than EQ-5D. CONCLUSIONS: Both EQ-5D and SF-6D appeared to be valid preference-based measures in Chinese COPD patients. SF-6D was more efficient in detecting differences among subgroups with differing health status. EQ-5D and SF-6D measured different things and might not be used interchangeably in COPD patients.