- May 27, 2015
- Reaction score
The antibody tests (Like the swab-PCR tests) can produce some false negatives if:Here’s a good article on testing, false positives, what it means:
As coronavirus antibody tests become available in Maryland, they offer more 'peace of mind’ than protectionLindsey Ellison was sick in December, an extreme cough-headache-energy-zapping kind of sick. By the time she recovered in January, news of the coronavirus began spreading. But she didn’t suspect she was infected with it until she heard from a colleague who had been to Wuhan, China, the pandemic...news.google.com
There appears to be a high rate of false negatives with some of the antibody tests.
1. The blood sample is collected too soon (IgM less than 7 days of illness or if blood is collected before 2 to 3 weeks for the IgG assessment). Or if the blood sample is collected more than 2 weeks from disease start for the IgM
test. Unfortunately not all labs/physicians are aware of the time intervals and like rocketry, some test kit products are superior to others. Finally, if a patient has a transient or genetic immune deficiency, then there may not be antibodies generated even during the height of the disease.
2. The swab (RT-PCR) tests also have false negatives for example if the swab did not collect enough virus from the patient and also the test accuracy diminishes the later in disease period that the test is collected (about 70% accurate in week 1 but only 54% accurate in week 2 of disease according to a few studies).
In general more than one test (spread over time) is needed for those with persistent symptoms with an initial negative test.
I hope this helps Tony.