2. Materials and Methods

2.1. Source of Patients and Diagnosis Criteria
The information of a total of 115 patients with confirmed COVID-19 who were admitted to Tianyou Hospital affiliated to the Wuhan University of Science and Technology between January 18, 2020, and March 5, 2020, was collected. The confirmed patients had a positive result of the nucleic acid test of SARS-CoV-2 by real-time fluorescence RT-PCR. Three clinical disease assessments were conducted using laboratory data collected. Cases of hospital discharge, death, and under treatment with a duration of hospitalization longer than 14 days prior to March 5, 2020, were studied. Cases with incomplete laboratory data or with a duration of hospitalization shorter than 14 days prior to March 5, 2020, were excluded. This study was approved by the Medical Ethics Review Board of Wuhan University of Science and Technology (No. 202009).

2.2. Clinical Classifications

2.2.1. Case Identification
According to the Guidance for Corona Virus Disease 2019: Prevention, Control, Diagnosis, and Management edited by the National Health Commission of the People's Republic of China, all cases were identified into four categories of mild cases, ordinary cases, severe cases, and critical cases. (1) Mild cases had mild clinical symptoms and no pneumonia manifestation in imaging. (2) Ordinary cases had symptoms like fever and respiratory tract symptoms, and pneumonia manifestation can be seen in imaging. (3) Severe cases met any of the following: respiratory distress, RR ≥ 30 breaths/min; the oxygen saturation is less than 93% at a rest state; or arterial partial pressure of oxygen (PaO2)/oxygen concentration (FiO2) ≤ 300 mmHg (1 mmHg = 0.133 kPa). Patients with >50% lesion progression within 24 to 48 hours in pulmonary imaging were treated as severe cases. (4) Critical cases met any of the following: respiratory failure occurs, and mechanical ventilation is required; shock occurs; or complicated with other organ failure that requires monitoring and treatment in ICU.

2.2.2. Outcome of Illness
According to clinical progression, outcomes in endpoints were divided into four types: hospital discharge, improved, exacerbation, and death.

2.3. Data Collection
The laboratory data were collected at three time points: admission, 3-5 days of hospitalization, and at the composite endpoint. DD, PT, APTT, and Fg were obtained and labeled as DD1-3, PT1-3, APTT1-3, TT1-3, and Fg1-3, respectively. Meanwhile, case identification, imaging identification, and outcome of illness were defined.

2.4. Statistical Methods
Statistical analysis was conducted using the SPSS 25.0 software. Descriptive statistics included means and standard deviations. The Kruskal-Wallis H-test and independent sample chi-square test were used to analyze differences between groups. The Receiver Operating Characteristic curve (ROC curve) was used to calculate the area under the curve (AUC) of DD and PT in order to evaluate the sensitivity and specificity of these factors in predicting mortality and hospital discharge. Spearman's rank correlation analysis was utilized to measure the degree of correlation between the hierarchically ordered variables in this study. A P value < 0.05 was considered statistically significant.

2.5. Patient and Public Involvement
This was a retrospective case series study, and no patients were involved in the study design, setting the research questions, or the outcome measures directly. No patients were asked to advise on the interpretation or writing up of results.