To identify the relationship between laboratory values in hospitalized COVID-19 patients upon admission and disease severity and mortality, a systematic review and meta-analysis was conducted utilizing four databases between December 2019 and May 2020. Weighted mean differences and confidence intervals for 27 laboratory markers associated with disease severity were calculated in each of the 64 studies included in the analysis. Most markers showed statistically significant association with both disease severity and mortality. Specifically, the results showed that hyperinflammation, blunted adaptive immune response, and intravascular coagulation play important roles in COVID-19 pathogenesis. There were no significant associations between sex or age of adult for any of the included markers. Thus, the authors suggest that patients with markers related to the previously listed processes are suitable for early intervention.