Lymphopenia and IgG2 subclass deficiency in patients with severe COVID-19 pneumonia

BACKGROUND: COVID-19 caused by the novel severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) manifests with a range of disease severities. A small proportion of COVID-19 patients are severely ill; however, a significant proportion of these patients are critically ill, and require admission and mechanical ventilation, which is associated with a high mortality. OBJECTIVE: To identify factors that may predispose patients with COVID-19 to severe disease that requires mechanical ventilation (MV). METHODS: We performed a retrospective audit of patients admitted with COVID-19 pneumonia to the intensive care unit (ICU) and medical wards to evaluate the potential associations between comorbid conditions, lymphopenia and IgG subclass deficiency with a need for MV. RESULTS: A total of 51 patients were included in the study. Almost half of the patients (47%; n=24) were documented to have IgG2 deficiency, 43% (n=22) had lymphopenia and 37% (n=19) had combined lymphopenia and IgG2 subclass deficiency. Of the 24 patients who required MV, 75% had IgG2 subclass deficiency, 73% had lymphopenia and 50% had both. The relative risk for requiring MV was 2.64, 3.38 and 2.81 for lymphopenia, IgG2 subclass deficiency and both, respectively. CONCLUSION: These findings suggest that lymphopenia, low IgG2 concentrations or the combination of both may be used to identify patients with severe COVID-19 that are at increased risk for MV. This may facilitate earlier identification of patients at high risk, who may benefit from more intensive therapy.