PCR Ct Values: Arbitrary & Meaningless

For those who don’t know how they determine someone positive for “Coronavirus” using the PCR test, it is not done with a binary + or – result like a pregnancy test. They determine positivity using an arbitrary (random) number called the Ct (cycle threshold) value. What is the Ct value?

Ct Value: the number of cycles required for the fluorescent signal to cross the threshold (ie exceeds background level).

Why does this Ct value matter?

Because the PCR test used to diagnose and label someone positive is nothing more than an expensive Xerox machine copying and doubling the amount of genetic material with each cycle (Ct). It is assumed that the lower the Ct value (i.e. the less copies they make to get a fluorescent reaction), the more “infectious” and sick a person is, but this is not always the case.

Per the late David Crowe:

“The PCR algorithm is cyclical. At each cycle it generates approximately double the amount of DNA (which, in RT-PCR, corresponding to the RNA that the process started with). When used as a test you don’t know the amount of starting material, but the amount of DNA at the end of each cycle will be shown indirectly by fluorescent molecules that are attached to the probes. The amount of light produced after every step will then approximately double, and when it reaches a certain intensity the process is halted and the sample is declared positive (implying infected). If, after a certain number of cycles, there is still not sufficient DNA, then the sample is declared negative (implying not infected). This cycle number (Ct) used to separate positive from negative is arbitrary, and is not the same for every organization doing testing. For example, there is a paper published that reported using 36 as the cutoff for positive, 37-39 as indeterminate, requiring more testing, and above 39 as negative. Another paper used 37 as the cutoff, with no intermediate zone. In a list of test kits approved by the US FDA one manufacturer each recommended 30 cycles, 31, 35, 36, 37, 38 and 39. 40 cycles was most popular, chosen by 12 manufacturers, and one each recommended 43 and 45.”


As you can see, the Ct value is not standardized, meaning that each test has a different Ct value used to determine whether someone is positive or negative. The vast majority of the PCR tests have Ct values over 35 with the most popular being 40 cycles. In other words, you could be positive using one test with a Ct value of 40 and negative on a different one with a Ct value of 35. You can even go from positive to negative to positive and vice versa using the same exact test if the Ct value fluctuates.

David also pointed out examples where this flipping between positive and negative occured in early studies:

There are now several papers that illustrate essentially impossible testing results. A paper from China reported on consecutive testing results, defined as either Negative (N), Positive (P) or Dubious (D, presumably intermediate). Results for 29 people with inexplicable results out of about 600 patients were: 1 DDPDD 2 NNPN 3 NNNPN 4 DNPN 5 NNDP 6 NDP 7 DNP 8 NDDPN 9 NNNDPN 10 NNPD 11 DNP 12 NNNP 13 PPNDPN 14 PNPPP 15 DPNPNN 16 PNNP 17 NPNPN 18 PNP 19 NPNP 20 PNPN 21 PNP 22 PNP 23 PNP 24 PNDDP 25 PNPNN 26 PNPP 27 PNP 28 PNPN 29 PNP. A study from Singapore did tests almost daily on 18 patients and the majority went from Positive to Negative back to Positive at least once, and up to four times in one patient. In China they have found that 5-14% of patients who have been cleared, with two consecutive negative tests, have later tested positive again, usually without new symptoms. In South Korea they recently reported 91 such patients. A 68 year old Chinese man went to hospital with symptoms, and tested positive. After his symptoms resolved and he tested negative twice he was released. But he tested positive again, and was readmitted, was released again, tested positive again, was readmitted, and then was released for a third time.”

Examples of high Ct Values which could flip between positive/negative based on the test cutoff.

This reliance on random high Ct values is a huge problem as explained by excerpts from David Crowe’s conversation with PCR expert Professor Stephen Bustin:

“Implicit in using a Ct number is the assumption that approximately the same amount of original RNA (within a multiple of two) will produce the same Ct number. However, there are many possibilities for error in RT-PCR. There are inefficiencies in extracting the RNA, even larger inefficiencies in converting the RNA to complementary DNA (Bustin noted that efficiency is rarely over 50% and can easily vary by a factor of 10), and inefficiencies in the PCR process itself. Bustin, in the podcast, described reliance on an arbitrary Ct number as “absolute nonsense, it makes no sense whatsoever”. It certainly cannot be assumed that the same Ct number on tests done at different laboratories indicates the same original quantity of RNA.

Professor Bustin stated that cycling more than 35 times was unwise, but it appears that nobody is limiting cycles to 35 or less (the MIQE guidelines recommend less than 40). Cycling too much could result in false positives as background fluorescence builds up in the PCR reaction.”

So according to Professor Bustin, any Ct value over 35 is unwise and the higher you go, the greater the chance of false-positives. Yet the vast majority of PCR tests are 35 and above. On top of that, the exact meaning behind a certain Ct Value is unknown. They do not know if a Ct of 20, 30, or even 35 is to be considered “infectious” or not.

According to this CDC study:

“The exact RT-PCR Ct values associated with the presence of infectious SARS-CoV-2 is unknown


Also according to the CDC:

“Q. Can cycle threshold (Ct) values be used to access when a person is no longer infectious?

A. No. Although attempts to culture virus from upper respiratory specimens have been largely unsuccessful when Ct values are in high but detectable ranges, Ct values are not a quantitative measure of viral burden. In addition, Ct values are not standardized by RT-PCR platform nor have they been approved by FDA for use in clinical management. CDC does not endorse or recommend use of Ct values to assess when a person is no longer infectious.


So if one were to ask the CDC:

  • The Ct value representing “infectiousness” is unknown
  • Ct values are not a quantitative measure of “viral” burden
  • Ct values are not standardized across platforms
  • Ct values are not FDA approved for use in clinical management
  • Ct values can not be used to determine if one is no longer “infectious”

This obviously raises the question, if the CDC admits all of this, why is the Ct value being used to determine one is infectious in the first place???

Even though the CDC/FDA does not endorse Ct values, according to this brief report published in the European Journal of Clinical Microbiology & Infectious Diseases, an inference is made about the correlation between Ct value and infectiousness:

“Correlation between successful isolation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in cell culture and cycle threshold (Ct) value of quantitative reverse transcription polymerase chain reaction (RT-PCR) targeting E gene suggests that patients with coronavirus disease 2019 (COVID-19) with Ct above 33 to 34 are not contagious and can be discharged from hospital care or strict confinement, according to a brief report published in the European Journal of Clinical Microbiology & Infectious Diseases.

Based on this data, researchers deduced that patients with Ct values > 34 do not excrete infectious viral particles and thus may be discharged.

Strong Inverse Correlation Between SARS-CoV-2 Infectivity and Cycle Threshold Value

So according to this report, a Ct value above 33 is considered not infectious. A report from the New York Times also backed up this assessment of non-infectiousness with Ct’s above 33 as well as pointing out the problems of relying on overly high Ct values to claim a person is positive:

Your Coronavirus Test Is Positive. Maybe It Shouldn’t Be.

One solution would be to adjust the cycle threshold used now to decide that a patient is infected. Most tests set the limit at 40, a few at 37. This means that you are positive for the coronavirus if the test process required up to 40 cycles, or 37, to detect the virus.

Tests with thresholds so high may detect not just live virus but also genetic fragments, leftovers from infection that pose no particular risk — akin to finding a hair in a room long after a person has left, Dr. Mina said.

Any test with a cycle threshold above 35 is too sensitive, agreed Juliet Morrison, a virologist at the University of California, Riverside. “I’m shocked that people would think that 40 could represent a positive,” she said.

A more reasonable cutoff would be 30 to 35, she added. Dr. Mina said he would set the figure at 30, or even less. Those changes would mean the amount of genetic material in a patient’s sample would have to be 100-fold to 1,000-fold that of the current standard for the test to return a positive result — at least, one worth acting on.”

“The C.D.C.’s own calculations suggest that it is extremely difficult to detect any live virus in a sample above a threshold of 33 cycles. Officials at some state labs said the C.D.C. had not asked them to note threshold values or to share them with contact-tracing organizations.”

“Officials at the Wadsworth Center, New York’s state lab, have access to C.T. values from tests they have processed, and analyzed their numbers at The Times’s request. In July, the lab identified 872 positive tests, based on a threshold of 40 cycles.

With a cutoff of 35, about 43 percent of those tests would no longer qualify as positive. About 63 percent would no longer be judged positive if the cycles were limited to 30.

In Massachusetts, from 85 to 90 percent of people who tested positive in July with a cycle threshold of 40 would have been deemed negative if the threshold were 30 cycles, Dr. Mina said. “I would say that none of those people should be contact-traced, not one,” he said.”

It’s just kind of mind-blowing to me that people are not recording the C.T. values from all these tests — that they’re just returning a positive or a negative,” said Angela Rasmussen, a virologist at Columbia University in New York.”


From this NYT article it is clear that Ct values are set too high. Some of the experts believe they should be set at 30 or lower. The report even shows how arbitrarily lowering the numbers of positive tests in certain states would have made up to 90% of the positives no longer so.

Looking at those Ct values of the tests one more time clearly shows they are set far too high according to the experts:

“In a list of test kits approved by the US FDA one manufacturer each recommended 30 cycles, 31, 35, 36, 37, 38 and 39. 40 cycles was most popular, chosen by 12 manufacturers, and one each recommended 43 and 45.”

Bustin’s advice in my interview with him was that not more than 35 cycles be used. With either 35 or less than 40, the majority of COVID-19 RT-PCR tests approved by the FDA may be pushing RT-PCR to its limits or beyond.”

Click to access FDATestSummary.pdf

In summary, we see nearly all PCR tests going above and beyond the 33 value and well beyond Professor Bustin’s 35. The arbitrary Ct values make the PCR test results absolutely MEANINGLESS beyond the fact that it does not actually detect any “virus” but only small fragments of RNA never proven to belong to one. Randomly choosing a Ct cutoff can be the difference between whether one is positive according to PCR or not. With how easy it is to manipulate the outcome of a positive/negative result as well as the fact that there is no evidence backing up the arbitrary Ct values chosen to determine one positive or not, there is absolutely no way the results of these tests should ever be trusted.



  1. And let’s not forget Fauci’s famous interview on This Week in Virology podcast July 17, 2020 in which he stated Ct values over 35 are not replicable by culturing and are just “dead nucleotides” and do not show active infection. No matter, got to keep the case numbers up and the pandemic fear porn humming along. What a farce this is!

    Liked by 1 person

      1. But they have been challenged, as you pointed out, even the NY Times denounced the fraud. Unfortunately, it’s hard to compete with 40 years of Hollywood virus horror movies. If only Hollywood had made one where the victims temporarily lost their sense of taste and smell!

        Liked by 2 people

      2. Lol, yes anosmia has been around for a long time. It just wasn’t a symptom that was flaunted/discussed regularly and was therefore underreporfed. It amazes me whenever people try to claim it as a new symptom of disease even though it has been linked to allergies, the common cold, the flu, air pollution exposure, etc. They have done a great job brainwashing the masses unfortunately.

        Liked by 1 person

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