INTRODUCTION: The ongoing worldwide pandemic of coronavirus disease 2019 (COVID19) has posed a huge threat to global public health. However, the issue as to whether routine blood tests could be used to monitor and predict the severity and prognosis of COVID19 has not been comprehensively investigated so far. OBJECTIVES: This study aimed to provide an overview of the association of markers in the routine blood test with the severity of COVID19. METHODS: PubMed, Embase, Cochrane Library, Wanfang, and China National Knowledge Infrastructure (CNKI) databases were searched to identify studies reporting data on markers in the routine blood test and the severity of COVID19, published until March 20, 2020. The STATA software was used for metaanalysis. RESULTS: A total of 15 studies with 3090 patients with COVID19 were included in this analysis. Patients in the nonsevere group, compared with those in the severe group, had lower counts of white blood cells (weighted mean difference [WMD], -0.85 [x109/l]; 95% CI, -1.54 to -0.16; P = 0.02) and neutrophils (WMD, -1.57 [x109/l]; 95% CI, -2.6 to -0.54; P = 0.003), greater counts of lymphocytes (WMD, 0.29 [x109/l]; 95% CI, 0.22-0.36; P <0.001) and platelets (WMD, 19.05 [x109/l]; 95% CI, 3.04-35.06; P = 0.02), and a lower neutrophiltolymphocyte (NLR) ratio (WMD, -2.48; 95% CI, -3.81 to -1.15; P <0.001). There was no difference in the monocyte count (WMD, 0.01 [x109/l]; 95% CI, -0.01 to 0.03; P = 0.029) between these 2 groups. Sensitivity analysis and metaanalysis based on standard mean difference did not change the conclusions regarding neutrophils, lymphocytes, and NLR, but yielded inconsistent results for white blood cells and platelets. CONCLUSIONS: Severe patients had more neutrophils, higher NLR level, and fewer lymphocytes than non-severe patients with COVID-19. Measurement of these markers might assist clinicians to monitor and predict the severity and prognosis of COVID-19.