A low Ct value on PCR indicates a lot of viral RNA is in the sample. It’s generally considered that people with a Ct value over 30 don’t present a significant infection risk1, 2, 3, 4, 5, 6 and presence of viral RNA may well be from a past infection. You can see from the graph above how closely the MFX test correlates with positivity on PCR in those most likely to be infectious.
The Ct30 threshold is based on a combination of of antigen sensitivity and studies of virus culture by Ct, where the presence of culturable virus is assumed to correlate with infectivity7.
Figures above independently verified in clinical samples by the Hampshire Hospitals NHS Foundation Trust