BACKGROUND: Although the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral load in respiratory specimens has been widely used to diagnose coronavirus disease 2019 (COVID-19), it is undeniable that serum SARS-CoV-2 nucleic acid (RNAemia) could be detected in a fraction of COVID-19 patients. However, it is not clear whether testing for RNAemia is correlated with the occurrence of cytokine storms or with the specific class of patients. METHODS: This study enrolled 48 patients with COVID-19 admitted to the General Hospital of Central Theater Command, People's Liberation Army, a designated hospital in Wuhan, China. The patients were divided into 3 groups according to the Diagnosis and Treatment of New Coronavirus Pneumonia (sixth edition) guidelines issued by the National Health Commission of China. Clinical and laboratory data were collected, and the serum viral load and interleukin 6 (IL-6) level were determined. RESULTS: Analysis of clinical characteristics of 48 cases of COVID-19 showed that RNAemia was diagnosed only in the critically ill group and seemed to reflect the severity of the disease. Furthermore, the level of the inflammatory cytokine IL-6 in critically ill patients increased significantly, almost 10 times that in other patients. More importantly, the extremely high IL-6 level was closely correlated with the detection of RNAemia (R = 0.902). CONCLUSIONS: Detectable serum SARS-CoV-2 RNA (RNAemia) in patients with COVID-19 was associated with elevated IL-6 concentration and poor prognosis. Because elevated IL-6 may be part of a larger cytokine storm that could worsen outcome, IL-6 could be a potential therapeutic target for critically ill patients with an excessive inflammatory response.