The ICMR (Indian Council of Medical Research) recently introduced a standard Ct value to ascertain Covid-19 positivity in patients. Ct or Cycle Threshold is a determinant that surfaces during RT-PCR tests. Under this new guideline, all patients manifesting a Ct value less than 35 are considered positive for Covid-19, while those with a Ct value above 35 are deemed negative.
Understanding RT-PCR Tests
RT-PCR (Reverse Transcription Polymerase Chain Reaction) tests are at the heart of Covid-19 detection. In these tests, swab samples from patients are collected and extracted for RNA (Ribonucleic acid). This RNA is subsequently converted into DNA (Deoxyribonucleic acid), setting the stage for amplification.
Amplification, in this context, refers to the process of producing multiple replicas of this genetic material – DNA. This replication enhances the test’s ability to detect the presence of the virus. The amplification occurs in cycles, beginning with one copy which then becomes two, four, and so on. After several cycles, a detectable amount of virus is produced.
The Role of Ct Value
Ct value, or Cycle Threshold, pertains to the number of cycles required before the virus can be detected. A higher number of cycles indicates that the virus remained undetected at a lower cycle count. Therefore, the lower the Ct value, the higher the viral load – implying that the virus has been identified after fewer cycles.
Additionally, research has suggested a significant correlation between Ct values and the time since the onset of symptoms as opposed to the severity of the disease.
Deciphering Viral Load
Viral Load denotes the quantity of a virus’s genetic material, typically RNA, present in an infected individual’s bloodstream. It is calculated as the total number of viral particles per millilitre of blood. Simply put, a higher viral load indicates rapid virus replication and progression of the infection.
A person displaying a high viral load is more prone to shed increased virus particles, a phenomenon known as “viral shedding”. Understanding viral load informs healthcare professionals about the stages of the disease and helps design an effective treatment strategy.
In conclusion, the ICMR’s new cut-off for Ct value offers a standard measure to determine Covid-19 positivity. This move simplifies the interpretation of RT-PCR tests, making it easier to track the virus’s presence and spread.
