Question

pcr and antibody antigen tests are used to detect covid19 , two cases for each test where you might get negative result for infected person, what are these cases?

Answer 1

Two cases for PCR testing for negative results for infected person

1.The sample collection from the nasal cavity is difficult some times and can't collect the enough genetic material of virus to detect in RT PCR or in early infection,viral genectic material will not be enough for reverse transcription and might give false negative result.

2. The false negative result may come from the poor processing of the swab material while extracting the RNA and converting into DNA in PCR .

Two cases for antibody-antigen testing for negative results for infected person

1. Due to slow immune response from the body, IgM doesn't appear high in the blood until 9 days and thus it doesn't get detected even if person is infected with virus.

2. IgG takes longer time to appear in blood comapre to IgM .If person's immune system is not strong enough to fight off the covid infection,then it might not appear in blood in testing. It genrally takes 11 days to appears in blood .it depends on person's own immune response. in this case also, it may give false negative for infected people.