WHO Information Notice for IVD Users 2020/05

Description of the problem: WHO requests users to follow the instructions for use (IFU) when interpreting results for specimens tested using PCR methodology.  

WHO guidance Diagnostic testing for SARS-CoV-2 states that careful interpretation of weak positive results is needed (1). The cycle threshold (Ct) needed to detect virus is inversely proportional to the patient’s viral load. Where test results do not correspond with the clinical presentation, a new specimen should be taken and retested using the same or different NAT technology.

WHO Information Notice for IVD Users 2020/05

In other words, any cycles above 18 are going to generate more false positives, and 30 cycles can generate 100 percent false positives.