Researchers from Toyama University and the Toyama Institute of Public Health have found a direct correlation between the amount of SARS-CoV-2 virus RNA in a patient’s blood and the severity of COVID-19.
To determine the presence of SARS-CoV-2 in the body, scientists use a polymerase chain reaction method with reverse transcriptase: it can be used to understand the presence of viral RNA in the nasopharynx from where a smear is taken.
Japanese scientists decided to test whether the disease’s clinical severity correlates with the presence of the virus in the blood, not in the nasopharynx.
To test this idea, they conducted a retrospective study of 56 patients admitted with COVID-19 to multiple Japan centers between April 13 and September 28, 2020. The researchers compared the viral RNA tests in their blood with PCR tests from the nasopharynx collected within seven days of the serum sample.
The patients were divided into several groups:
- Lungs. Symptoms but no pneumonia;
- Moderate. With pneumonia that did not require supplemental oxygen;
- Heavy. Those that require additional oxygen;
- Critical. Those who required invasive mechanical ventilation or developed shock and multiple organ dysfunction.
The study results showed that in critical patients, RNA emission was observed in 100 percent of cases, in severe patients – in half, in moderate patients – in 4 percent of cases, and in mild and asymptomatic patients, it was not at all.
As a result, the authors of the study’s hypothesis was confirmed: by the amount of viral RNA in the blood, one can judge the severity of the course of the disease.
Interestingly, the viral load determined by the PCR test did not correlate with the level of RNA emission determined by the blood test taken on the same day.