A drop in arterial oxygen saturation when moving from a supine to an upright position.

Non-specific markers like digital clubbing (swelling of fingertips), cyanosis (bluish skin tint), and spider nevi (spider-like veins) may also be present. Diagnostic Criteria Diagnosis is confirmed through the following findings: A Case of Hepatopulmonary Syndrome - PMC

While many patients are initially asymptomatic, those who develop symptoms often experience:

Shortness of breath, particularly during physical exertion.