What Is a PCR Test Cycle, Used in COVID Testing?
Recently, the WHO (World Health Organization) announced 'guidance' that COVID testing labs and facilities should lower the number of PCR cycles used to evaluate tests.
On the political front, this was perceived by many experts, legislators, and even knowledgeable citizens as a long time coming. As a result, according to multiple news reports, positive COVID tests have begun to drop significantly.
Last August, MSN's Lifestyle section ran an article that also appeared in the (London) Daily Mail newspaper, basically saying COVID tests sensitivity levels were set too high, resulting in false-positive results.
What is a PCR test? It analyzes genetic matter from the virus, and determines if a person has the virus.
Last October, the website Swiss Policy Research ran a story entitled The Trouble with PCR Tests. It looked at all the potential issues that could taint or modify a result; from outside contamination to running too many cycles in an effort to determine a result.
This article said some European labs run 30-40 cycles, while US labs have run 35-45. Many are running on 45. Think of cycles as 'attempts' to analyze the DNA.
Doctors, according to the MSN article, say running fewer cycles will provide more accurate testing. A person who is truly 'suffering' from COVID and has a lot of the virus in their body will test accurately positive with fewer cycles. It won't take as many cycles to detect a truly infected and contagious person because there's a lot more virus present.
Running upwards of 45 cycles (or attempts) can result in smaller possible amounts of COVID to show up, but they might be not enough to cause any health issues.
According to the Swiss Policy Research story:
"...This means that if a person gets a “positive” PCR test result at a cycle threshold of 35 or higher (as applied in most US labs and many European labs), the chance that the person is infectious is less than 3%. The chance that the person received a “false positive” result is 97% or higher."
So, this is what all that talk about PCR cycles is about, in layman's terms. It explains why multiple news reports say case counts are dropping, and in some areas, dropping fast. If possible, we are going to try to find out what cycle rate is being used for tests in Washington state.