A new study has revealed that tests to detect antibodies to SARS-CoV-2 are most sensitive among people aged 40 to 59 years compared with other age groups.

The study, published in the journal Jama Network Open, revealed significantly higher sensitivity among males compared with females.

Test sensitivity was highest at 126 days after positive RT-PCR results for males and 133 days after positive RT-PCR results for females, the authors wrote.

The researchers of the study noted that the optimal time to test for an antibody response appears to be about four months after a PCR-positive SARS-CoV-2 result.

“The punchline is that it is actually possible to measure antibody levels too early, too soon after a SARS-CoV-2 test,” senior study author Atul J. Butte, MD, Ph.D., director of the Bakar Computational Health Sciences Institute at the University of California San Francisco, told Medscape Medical News.

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He added: “As would be expected, it does take a few weeks for the body to form a detectable antibody response.”

“The effect of age and sex on the sensitivity of the test is almost certainly linked to viral load. We know that men are more susceptible to Covid than women, and older people are more badly affected than younger people and tend to have higher viral loads,” Eleanor M. Riley, Ph.D., told Medscape Medical News.”

“The higher the viral load, the stronger the kick to the immune system, and therefore the more antibodies that are made,” Riley further said.

Methodology

For the study, the researchers at the University of California conducted antibody tests between February 1 and October 15, 2020.

Butte said: “In our study, we looked at patients who we saw had a positive SARS-CoV-2 test, and only 75 per cent to 80 per cent had a positive antibody level. We would have expected 100 per cent of them to have antibodies after SARS-CoV-2 infection. The current research did not address why.”

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