D-dimer levels and COVID-19 severity: Systematic Review and Meta-Analysis.

Coronavirus disease 2019 (COVID-19) is a fatal and pandemic disease discovered in December 2019 in Wuhan, with lots of asymptomatic cases and a long incubation period. The researchers suggested that high d-dimer levels could predict disease severity, lung complications, and thromboembolic events before they occur. We searched in PubMed, Scopus, and Web of Science using the keywords "D-dimer" and "coronavirus" or "D-dimer" and "COVID-19." We used Standardized Mean Differences (SMD) to build forest plots of continuous data and assess differences in serum D-dimer concentrations between severe and non-severe patients with COVID-19 disease. We evaluated p-value < 0.05 as statistically significant and preferred 95% confidence intervals (CIs). The pooled results of all studies revealed that the D-dimer concentrations were significantly higher in patients with more severe COVID-19 (SMD: 2.32 μg/mL; 95% CI, 0.72 3.92 μg/mL, p< 0.001). We evaluated severe patients with total D-dimer levels. D-dimer concentrations were significantly higher in severe patients against total COVID-19 patients (SMD: 2.01 μg/mL; 95% CI, 0.25 to 3.77 μg/mL, p= 0.08). We do not know the D-dimer increment mechanism in severe patients yet, but we think that these findings will be useful in the early diagnosis of severe disease and the first treatment.