CD4 and lymphopenia: Patients with severe COVID-19 always have lymphopenia and decreased numbers of CD4+ T cells, CD8+ T cells, B cells, and natural killer cells.[1,36,37] Wynants et al performed a systematic review by constructing prediction models for COVID diagnosis and prognosis,[38] showing that CRP and lactic dehydrogenase levels and lymphocyte counts were the most commonly mentioned predictors.