As the pandemic progresses, scientists are striving to understand more about the virus, its spread, and how best to detect and measure it. Among the tools in our arsenal for understanding and battling this disease is the RT-PCR (Reverse Transcription Polymerase Chain Reaction) test. Recent research has revealed that the Ct (Cycle Threshold) values resulting from these tests can vary substantially, causing confusion and prompting further investigation.
Understanding The Variability In Ct Values
A survey of 700 laboratories across the US using standardized proficiency testing material found a significant variability in Ct values. The difference could be as much as 14 cycles, even within the same lab conducting the same test. There were variances of up to 3 cycles discovered for different target genes, and up to 12 cycles for the same target gene across differing labs.
One reason for this variability may be due to the dynamic nature of Ct values. For instance, a low Ct value at the time of diagnosis doesn’t mean it will remain low the following day. Conversely, a high Ct value early in the infection could decrease if repeated a day or two later. As such, there is currently no conclusive correlation between Ct values and disease severity.
Technical and logistical factors may also contribute to Ct value variability. Factors such as how specimens are collected, what kind of specimen is used, the medium of transport for the swab, and the time lag between collection and processing can all influence the amount of viral genetic material present and, subsequently, the Ct value.
RT-PCR Tests And Ct Values: An Overview
To comprehend the importance of Ct values, it’s essential to understand the RT-PCR test. In this test, RNA (Ribonucleic acid) is extracted from a patient’s swab and converted into DNA (Deoxyribonucleic acid). This DNA is then amplified, creating multiple copies of the material to improve the detection capacity of the test. Through a series of cycles, a detectable amount of virus is produced.
Ct, or ‘Cycle Threshold’, signifies the number of cycles after which the virus is detectable. The higher the number of cycles needed, the harder the virus was to detect initially. Inversely, a lower Ct value indicates a higher viral load, as the virus was detected after fewer cycles.
Insights On Viral Load
The term “viral load” refers to the amount of virus in an infected person’s blood, usually expressed as the total number of viral particles present in each milliliter of blood. This measurement gives insight into the progression of the infection -a high viral load indicates rapid replication and the likelihood of the patient shedding more virus particles. Studies have shown that the time since the onset of symptoms has a closer relationship with Ct values than the severity of the disease.
Further research into these areas is imperative for understanding the course of the disease and improving diagnostic accuracy. This will allow us to better prepare for and mitigate the impact of this pandemic.
