Exhaled breath analysis in hepatology: State-of-the-art and perspectives

Abstract

Liver disease is characterized by breath exhalation of peculiar volatile organic compounds (VOCs). Thanks to the availability of sensitive technologies for breath analysis, this empiric approach has recently gained increasing attention in the context of hepatology, following the good results obtained in other fields of medicine. After the first studies that led to the identification of selected VOCs for pathophysiological purposes, subsequent research has progressively turned towards the comprehensive assessment of exhaled breath for potential clinical application. Specific VOC patterns were found to discriminate subjects with liver cirrhosis, to rate disease severity, and, eventually, to forecast adverse clinical outcomes even beyond existing scores. Preliminary results suggest that breath analysis could be useful also for detecting and staging hepatic encephalopathy and for predicting steatohepatitis in patients with nonalcoholic fatty liver disease. However, clinical translation is still hampered by a number of methodological limitations, including the lack of standardization and the consequent poor comparability between studies and the absence of external validation of obtained results. Given the low-cost and easy execution at bedside of the new technologies (e-nose), larger and well-structured studies are expected in order to provide the adequate level of evidence to support VOC analysis in clinical practice.

Keywords: Exhaled breath analysis; Electronic nose; Gas chromatography; Breath print; Liver cirrhosis; Nonalcoholic fatty liver disease; Hepatic encephalopathy

Core tip: Since the liver plays a key metabolic role, different volatile organic compounds (VOCs) have been identified in the exhaled breath of hepatopathic patients. VOCs have been already analyzed with promising results concerning disease diagnosis and characterization. To date, translation to the clinic has been limited by the lack of standardization and external validation of the results obtained. Since VOC analysis with new technologies is easy, quick, and cheap, and it was proven to discriminate patients with liver cirrhosis, identify stage disease severity, and predict important adverse outcomes, it should be further explored and hopefully exported to clinical practice.