Published: 02-09-2020 09:58 | Updated: 02-09-2020 10:14

Virus in the blood can predict severe COVID-19

Danderyds hospital at autumn
Danderyd Hospital. Photo: Malin Wirf

A blood test on hospital admission showing the presence or absence of SARS-CoV-2 can identify patients at a high risk of severe COVID-19. Admitted patients without virus in their blood have a good chance of rapid recovery. This according to researchers at Karolinska Institutet and Danderyd Hospital in a new study published in the scientific journal Clinical Infectious Diseases.

Karl Hagman. Photo: Cecilia Larsson Lantz, Danderyd Hospital

Blood samples were taken from patients with a confirmed COVID-19 infection within three days of admission to the Department of Infectious Diseases, Danderyd Hospital, Sweden. Patients with measurable levels of the new coronavirus SARS-CoV-2 in their blood were seven times more likely to develop critical symptoms and eight times more likely to die within 28 days.

“This readily available test allows us to identify patient groups at high or low risk of severe COVID-19, which enables us to better guide the treatment and monitoring of these patients”, says the study’s lead author Karl Hagman, infectious diseases consultant at Danderyd Hospital and doctoral student at Karolinska Institutet’s Department of Clinical Sciences at the same hospital.

Standard hospital technique

The researchers analysed the presence of viral RNA in the blood using a standard hospital technique called PCR on samples taken from a total of 167 patients. Sixty-one patients had measurable levels of the virus in their blood and 15/61 (25 per cent) died within 28 days of blood sampling. This can be compared with three deaths (three per cent) amongst the 106 patients who did not have measurable levels of virus in their blood. The presence of virus in the blood increased with age and was much more common in patients over the age of 60.

The researchers received no specific funding for this study. The paper’s last author, Johan Ursing, has a clinical research position financed by Region Stockholm. One of the co-authors has reported receipt of payment from pharmaceutical company Pfizer outside this current study. No other potential conflicts of interest are declared in the paper.


“SARS-CoV-2 RNA in serum as predictor of severe outcome in COVID-19: a retrospective cohort study”. Karl Hagman, Magnus Hedenstierna, Patrik Gille-Johnson, Berit Hammas, Malin Grabbe, Joakim Dillner, Johan Ursing. Clinical Infectious Diseases, online 28 August 2020, doi: 10.1093/cid/ciaa1285.