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Tests for detecting antibodies to SARS-CoV-2 are more sensitive among people aged 40 to 59 years compared to other age groups – and significantly more sensitive in men than in women, a cohort study reveals.
Furthermore, the optimal time for testing for antibody response appears to be approximately 4 months after PCR-positive SARS-CoV-2 production.
“The punchline is that it is actually possible to measure antibody levels prematurely, prematurely after a SARS-CoV-2 test,” said study lead author Atul J. Butte, MD, PhD, director of the Institute of Computer Health Sciences Bakar at the University of California San Francisco, stated Medscape Medical News. “As expected, it will take the body a few weeks to produce a visible antibody response.”
The Letter of Inquiry was published online February 12 in Open JAMA Network.
“The effect of age and gender on test sensitivity is almost certainly related to viral loading,” said Eleanor M. Riley, PhD. Medscape Medical News when asked to comment. “We know that men are more prone to COVID than women, and older people are more affected than younger people and tend to have higher viral loads.”
“The higher the viral load, the stronger the kick to the immune system, and therefore the more antibodies that are made,” said Riley, who is affiliated with the Institute of Psychiatric and Disease Research and is a high Professor of immunology and infectious disease at the University of Edinburgh, United Kingdom.
Test throughout California
Together with lead author Rohit Vashisht, PhD, and colleagues, Butte studied 486 people tested for SARS-CoV-2 IgG antibodies following a chain-polymerase reuptake test (RT-PCR) test result for disease. They measured midday antibodies 34 days (interquartile range, 3 to 64 days) after the advanced RT-PCR test.
Antibody tests were performed between February 1 and October 15, 2020. These results and other study findings come from the University of California coronavirus infection 2019 research data set.
“In our study, we looked at patients we saw who received a positive SARS-CoV-2 test, and only 75% to 80% had a positive antibody level,” Butte said. “We would expect 100% of them to have antibodies after SARS-CoV-2 infection.” The current investigation did not address why, he said.
More meaningful for men
The study showed significantly higher sensitivity among males (0.79; 95% confidence interval [CI], 0.73 – 0.84) compared with women (0.72; 95% CI, 0.66 – 0.77; P.<.001).
Time made a difference too. “Patients who underwent their serological tests closer to their positive RT-PCR results were more likely to receive negative serological results than those who were tested later,” the researchers note. near. Test sensitivity was highest at 126 days after positive RT-PCR results for men and 133 days after positive RT-PCR results for women.
In addition, antibody tests were most sensitive for those aged 50 to 59 years (0.87; 95% CI, 0.78 – 0.94), and slightly less sensitive for those aged 40 to 49 years (0.83; 95% CI, 0.72 – 0.91; P. <.001).
Sensitivity varied according to commercial assay. For example, Beckman Coulter’s SARS-CoV-2 IgG test had the highest sensitivity of 0.84 (95% CI, 0.73 – 0.91). The LIAISON SARS-CoV-2 S1 / S2 IgG (DiaSorin) test had a maximum sensitivity of 0.78 (95% CI, 0.72 – 0.82) and the DZ-Lite SARS-CoV-2 IgG CLIA (Diazyme) test had a maximum sensitivity 0.67 (95% CI, 0.57 – 0.75).
The wait is worth it
Findings at the optimal antibody testing time at around 4 months “suggest that premature serological levels measurement after SARS-CoV-2 infection may lead to an incorrect assessment of immune response,” the researchers said. noting.
“Antibodies may not be detected in the first few days after infection – this is to be expected as an antibody response takes at least a week to become susceptible and tends to rise after about on 21 days, “Riley said.
Instead, someone with recent COVID-19 symptoms should take an antigen / PCR test, she said.
Caves and Future Research
The researchers cautioned that, even though sensitivity was higher in males and patients aged 40 to 59 years, “the cohort sizes of our subset are small. If these findings are confirmed, it is possible that differences in gender and age must be taken into account in defining serological levels. “
Preexisting conditions, clinical depth of disease, and non-service clinical factors may have altered sensitivity. Another possible limitation was that titer levels were not available, so antibody was considered binary-like (yes or no).
The investigation is ongoing, Butte said. “We are going to keep looking at these levels, to see how long after the infection we see patients with recognizable antibody levels. “
“It will be useful to see if patients still have recognizable antibody levels a year out after their first SARS-CoV-2 infection,” he said.
JAMA Netw Open . Published online February 12, 2021. Full text
Butte reported that he received donations from the U.S. Food and Drug Administration and the Robert Wood Johnson Foundation during the study’s review. Riley did not disclose any material financial relationships. The University of California Health System and its Center for Data-driven Insights and Innovation provided partial funding for this research.
Damian McNamarais an employeea Miami-based journalist. It covers a wide range of medical specialties, including infectious diseases, gastroenterology, and diagnostic care. Follow Damian on Twitter: @MedReporter.
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