The circular issued on Thursday stated CT Thorax has greater sensitivity (86%-98%) and lower false-negative rate than RT-PCR.

COVID labRepresentational image/PTI
news COVID-19 Friday, October 16, 2020 - 14:48

Due to rise in suspected false negative coronavirus results in RT-PCR (reverse transcription-polymerase chain reaction) tests among highly symptomatic patients, the Karnataka government has issued a circular to subject them to CT Thorax scans and other diagnostic methods. This has been done following the state expert committee recommendations aiming to reduce mortality by starting COVID-19 treatment at the earliest.

A circular issued by the Jawaid Akhtar, Additional Chief Secretary (Health and Family Welfare) on Thursday said, “Viral infections manifest as varied clinical syndrome, which are similar to many other pathogens. Hence, it is not possible to confirm the diagnosis of patients with COVID-19 or Influenza infection without a diagnostic test. And many times, in spite of clinical-radiological features suggestive of COVID-19 disease, the RT-PCR test, which is considered as a gold standard test, may be negative.”

 The circular stated CT Thorax has greater sensitivity (86%-98%) and lower false-negative rate than RT-PCR. It also noted with the increase in the spread of COVID-19 disease along with an increase in the number of tests every day, the percentage of false negatives are also increasing and it's expected to increase further in future.

Explaining the move, Dr CN Manjunath, nodal officer for COVID-19 testing in the state, said, this circular was issued as often patients’ families do not want to start treatment stating a negative RT-PCR test.

“This is a scientific way to establish if a patient is indeed suffering from COVID-19. When the patient is a contact of a positive person and there is a strong suspicion that the patient is also COVID-19 positive because of typical symptoms, they will be subjected to this test once the RT-PCR tests come back as negative. So if CT scan findings are also typical of COVID-19, we will treat those patients as COVID-19 positive. This is a standard practice globally. This circular has been issued so that there is no confusion among the kin of the patients,” Dr Manjunath told TNM.

Dr Manjunath said that even though the gold standard, RT-PCR tests can give false negative results if the sample is collected too early in the course of the disease or is improperly collected. He pegged the false negative results for COVID-19 in RT-PCR tests at 5-10% globally depending on various factors.

Doctors in Gandhi Medical College in Bhopal also  too had a similar experience. A Times of India article on October 13 had quoted doctors saying that among 20% critical COVID-19 cases, the RT-PCR tests had come negative.

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