BACKGROUND: Hepatologists have long sought to develop a test for assessing liver 
function, but this aim has been stalled by the complexity of the liver and its 
diverse functions. Results of metabolic tests, including breath tests, correlate 
with clinical and histological parameters of patients with liver disorders; 
however, these tests tend to be cumbersome and impractical for everyday use. The 
recent development of a real-time, point-of-care liver function breath test has 
made it straightforward to assess the metabolic function of the liver.
AIM: To review the available data on the use of breath tests for assessing liver 
reserve in various conditions and their application in various clinical 
hepatology settings.
RESULTS: The (13)C-methacetin breath test enables accurate follow-up of patients 
with acute or chronic liver damage, where overall hepatic function is 
significantly suppressed by known causes of liver disorders, including acute, 
sub-acute or chronic conditions. The metabolic breath test can detect both 
gradual and spontaneous improvements in liver function and the effects of 
treatment.
CONCLUSIONS: Breath testing that provides continuous quantification of 
methacetin metabolism may be a sensitive tool for the diagnosis and follow-up of 
patients with liver disorders.