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The term CT value in the PCR test (CT value PCR) is increasingly being discussed by many people. Some of them may already understand CT value PCR, but there are still many people who don't understand and ask questions about this term. So, what exactly is CT value PCR?
CT value or cycle threshold value is a value that appears in the PCR examination. CT value PCR serves to help determine the status of whether a person is positive or negative regarding Corona virus infection.
In addition, CT values can also help doctors to predict the possible amount of Corona virus in the body and determine the patient's risk of experiencing complications or severe symptoms of COVID-19.
Understanding CT Value in PCR Test Results
The RT-PCR (Reverse-Transcriptase Polymerase Chain Reaction) test is one of the examination methods to diagnose COVID-19 by detecting genetic material from the corona virus or SARS-CoV-2.
This test is generally recommended to be carried out on patients whose antigen swab results are positive, or have close contact with a confirmed patient of COVID-19.
In the PCR test results, there is a CT value that can be an indicator to determine the possible amount of virus in the patient.
This CT value refers to the number of amplification cycles or repeated examination of the sample until the Corona virus component can be detected by the PCR examination machine.
In general, the amplification process in the PCR examination will occur repeatedly until it reaches 40–45 cycles, depending on the laboratory. In laboratories that set a CT value of 40, this means that they repeat amplification to detect Corona virus DNA or RNA up to 40 times in the PCR test carried out.
If in the 40 repetitions the examiner succeeds in detecting the Corona virus, then the PCR test is declared positive. After that, the examiner will also attach to the amplification cycle how much genetic material of the Corona virus was found.
For example, if the DNA or RNA of the Corona virus in the sample is detected in the 20th cycle, then the result is a positive PCR with a CT value of 20. Meanwhile, if in 40 repetitions of PCR no Corona virus is found, then the results of the PCR test can be declared negative.
The Importance of Understanding CT Value PCR
The results of the PCR examination are actually sufficient to confirm a person's diagnosis is said to be positive or negative for being infected with the SARS-CoV-2 virus. However, the presence of CT value PCR also plays an important role for the following reasons:
Predicting the amount of virus in the body
The CT value can help doctors predict how much virus is in the patient's body.
As a rule of thumb, the lower the CT value or below 25–28, the more likely it is that the amount of Corona virus is increasing in the body. On the other hand, a high CT value or above 30–35 indicates that the number of viruses may be less.
However, until now there has been no research that can confirm the effectiveness or accuracy of the CT value PCR as a determinant of the amount of Corona virus in the body.
Monitoring the progress of the patient's condition
In addition to diagnosing COVID-19, the PCR test and its CT value can also be used to monitor changes in the amount of virus present in a person's sample over time.
In hospitalized COVID-19 patients, the PCR examination usually needs to be repeated 2-3 times, from the initial diagnosis, during treatment, until when the patient has improved and can go home.Meanwhile, for patients who are self-isolating at home, it is enough to carry out a PCR examination once for the diagnosis of COVID-19.
In treated patients, the criteria for improvement or recovery are stated based on clinical conditions, namely improvement in symptoms experienced, as well as positive PCR results to negative, or at least an increase in CT value to above 36.
Help doctors determine the steps for treating COVID-19
PCR test and CT value can be used to predict the severity of COVID-19 disease. This examination also plays an important role in helping doctors determine steps for handling and treating COVID-19 in patients, for example suggesting patients to self-isolate at home or refer patients to hospitals.
However, the CT value in the PCR test for COVID-19 cannot be used as the only benchmark for diagnosing COVID-19. To determine the severity and general condition of the patient, the doctor still needs to carry out a physical examination and supporting examinations, such as blood tests or chest X-rays.
Besides that, the CT value in PCR also has another drawback, namely it cannot distinguish between live viruses that can infect other people and viruses that have died in the body.
So, even if you already understand the CT value of PCR, you should avoid interpreting the CT value yourself without valid information from the doctor, OK? If you still have questions about CT value PCR, you can ask the doctor directly through the ALODOKTER application