To the Editor: Coronavirus disease 2019 (COVID-19) is widely spread and poses a critical threat to global health. 1 Prominent changes in coagulation function in severe patients of COVID-19 have been reported in a recent study. 2 Therefore, we conducted this quantitative meta-analysis to explore the difference in blood coagulation parameters between severe and mild cases of COVID-19. Literature published from December 1, 2019 to March 30, 2020 was searched systematically using PubMed and Embase without language limits. The keywords were: coronavirus, laboratory, clinical manifestations, clinical characteristics, and clinical features. All documents comparing information on coagulation parameters between mild and severe cases of COVID-19 patients were finally referred to in our meta-analysis. The pooled standardised mean difference (SMD) and 95% confidence interval (CI) were computed by applying the random-effect model using Stata software (STATA 14.0, Stata Corp, College Station, TX, USA). The study quality was measured by adopting an 11-item checklist, which was suggested by the Agency for Healthcare Research and Quality (AHRQ). Table I displays the main characteristics of the included studies. Nine studies, including one study from medRxiv, with 1105 patients were eventually included for detailed evaluation. Platelet count (PLT), activated partial thromboplastin time (APTT), prothrombin time (PT) and D-dimer (DD) levels were available in five, six, six and eight studies, respectively. All the studies were conducted in China. Quality score varied from 3 to 7 points, with a mean of 544 (Table I). All the studies were of moderate quality, except one of low quality.

The main difference in coagulation function between severe and mild COVID-19 patients is shown in Fig 1. Pooled results revealed that PT and DD levels were significantly higher in patients with severe COVID-19 (0468, 95% CI= 0443–0493, I2= 5347%; 0453, 95% CI= 0422–0484, I2= 7849%, respectively). However, no significant difference in PLT and APTT values between severe and mild patients was observed (À0408, 95% CI= À0434 to 0418, I2= 6045%; À0403, 95% CI= À0440 to 0434, I2= 7945%, respectively). Increasing values of DD and PT support the notion that disseminated intravascular coagulation (DIC) may be common in COVID-19 patients. 2 In addition, the rise of DD level also indicates secondary fibrinolysis conditions in these