Ct value

What does a Ct value mean?

How contagious a person is, depends primarily on how many viruses there are in the body. This can be estimated using the Ct value. The abbreviation Ct stands for "cycle threshold". The Ct value indicates the number of measurement cycles that the PCR procedure must run through in the laboratory, before the coronavirus is detected. 
A low Ct value indicates a high viral load, since only a few measurement cycles had to be performed to detect the virus. A low Ct value indicates that the affected person is likely to be infectious. 
A high Ct value indicates a low viral load and means that the person may no longer be infectious or that the infection is just beginning.

However, to make a definitive statement about how infectious a person is, other factors such as the quality and timing of the swab and the course of the disease must be considered. The current recommendations in the event of a positive test therefore apply regardless of the Ct value.