This study aims to develop a non-invasive and rapid diagnostic technology for acute upper gastrointestinal bleeding (AUGIB) by analyzing volatile organic compounds (VOCs) in exhaled breath. Clinically confirmed patients will be divided into three groups (no bleeding, minor bleeding, major bleeding) based on endoscopic findings. VOC profiles will be analyzed to construct a predictive model, validated for sensitivity and specificity (both targets ≥0.7). This approach addresses the limitations of endoscopy in emergency or resource-limited settings, improving diagnostic efficiency and reducing mortality.

Acute upper gastrointestinal bleeding (AUGIB) is a common emergency with an annual incidence of 100-180/100,000 and mortality of 2%-15%. Endoscopy, the gold standard, is invasive and equipment-dependent, limiting its use in primary care or emergencies. Exhaled breath VOCs analysis, a non-invasive and portable method, has been applied in other diseases but not yet explored for AUGIB.

Objectives:

1. Identify characteristic VOC profiles in exhaled breath of AUGIB patients.
2. Develop a VOC-based predictive model with sensitivity and specificity ≥0.7.
3. Establish rapid diagnostic criteria to enhance clinical decision-making.

Inclusion Criteria:

1. Age ≥18 years;
2. Clinical suspicion of AUGIB (e.g., hematemesis, melena);
3. Fasting ≥4 hours;
4. Signed informed consent.

Exclusion Criteria:

1. Severe pulmonary dysfunction or recent lung infection (within 1 week);
2. Cardiac/renal failure or disseminated intravascular coagulation;
3. Contraindications to endoscopy;
4. High-risk conditions (e.g., massive ascites);
5. Alcohol consumption within 24 hours;
6. Pregnancy.

Patients requiring endoscopy for suspected AUGIB