Efforts to identify circulating factors that predict severity of acute lung injury/acute respiratory distress syndrome（ALI/ARDS）patients is unrevealing. The primary purpose of this study is to verify circRNAs and microRNAs might be potential novel ALI/ARDS biomarkers and could play roles in pathogenesis of ALI/ARDS.

Acute lung injury (ALI) or acute respiratory distress syndrome (ARDS) is a devastating cause of morbidity and mortality characterized by alveolar epithelial and endothelial injury. Despite recent advances in pathogenetic mechanisms and therapy strategies of ALI, efforts to identify circulating factors that predict severity of ALI/ARDS patients have been unrevealing.

Circular RNAs (circRNAs) are a novel class of endogenous non-coding RNA with a covalently continuous closed-loop structure. Compared with traditional linear RNAs, circRNAs are more stable and resistant to RNase R due to the absence of 5' caps and 3' tails, which show clear advantages in acting as novel molecular biomarkers for many diseases. In addition, many studies have reported that circRNAs can bind to microRNAs (miRNAs), acting as "miRNA sponges" which are named competitive endogenous RNAs (ceRNAs), and can regulate gene expression at the transcriptional or post-transcriptional level. Evidence indicates that circRNAs play important roles in cancers and other diseases such as tuberculosis and intervertebral disc degeneration. As no published research has studied the expression and role of circRNAs in the pathology and pathogenesis of ALI/ARDS, the investigators aimed to validate the aberrant expression of circRNAs in ALI/ARDS and explore the potential pathological mechanism in which circRNAs are involved.

Inclusion Criteria:

• Clinical diagnosis of ALI/ARDS
• Informed consent was obtained from either the subjects themselves or from designated surrogates before enrollment in the study.

Exclusion Criteria:

• Patients who have chronic lung disease before enrollment.
• Patients who have severe organ dysfunction, autoimmune diseases and tumor.
• Women who are pregnant or breast-feeding.
• Patients who, in the opinion of the Investigator, have any other medical condition which renders the patient unable to complete the study or which would interfere with optimal participation in the study or produce significant risk to the patient.
• Patients participating in or planning to enroll in another clinical trial during the time of the study.

Patients with and without ARDS were screened from Changhai Hospital. Patients were enrolled consecutively over a 2-year time period (2017-2018). All enrolled patients with ALI met the American-European Consensus Committee criteria.In addition, healthy individuals were recruited from the general population.