The problem is that you may be in an early stage of infection where there isn't much virus, or the swab may not have caught much of it. You could also have alr

The problem is that you may be in an early stage of infection where there isn't much virus, or the swab may not have caught much of it. You could also have already recovered from an asymptomatic infection, and there is some residual viral RNA. A high Ct could be because of one of those factors, or from cross-contamination.