Scientists at the University of California analyzed data on antibody testing of 486 people a month or two after laboratory confirmation of SARS-Cov-2. The researchers expected that antibodies would be developed in all patients without exception, but it turned out that between 75% and 80% of people received positive test results during this period.
The study revealed an increased sensitivity of the tests in a certain group of patients: these are men from 40 to 59 years old. According to scientists, this is due to the fact that men, on average, have a higher viral load than women. The higher it is, the stronger the blow to the immune system and, therefore, the more antibodies are produced.
Scientists have also determined the optimal time to test for antibodies – four months after confirmation of COVID-19.
“Patients whose serologic tests were performed closer to positive PCR test results were more likely to get negative results compared to those who were tested later,” the researchers note. The sensitivity of the test was maximal 126 days after the detection of SARS-Cov-2 in men and 133 days in women.
Last June, the authors of the Cochrane Systematic Review reported that a week after the first symptoms of COVID-19, testing detects antibodies in only 30% of patients. Research accuracy increases to 72% after two weeks and up to 94% in the third week.
“If you run your tests too early, the odds are they won’t work,” says Jon Deeks, professor of biostatistics at the University of Birmingham and lead author of the review.