Today, the assessment of liver function in patients suffering from acute or 
chronic liver disease is based on liver biopsy and blood tests including 
synthetic function, liver enzymes and viral load, most of which provide only 
circumstantial evidence as to the degree of hepatic impairment. Most of these 
tests lack the degree of sensitivity to be useful for follow-up of these 
patients at the frequency that is needed for decision making in clinical 
hepatology. Accurate assessment of liver function is essential to determine both 
short- and long-term prognosis, and for making decisions about liver and 
non-liver surgery, TIPS, chemoembolization or radiofrequency ablation in 
patients with chronic liver disease. Liver function tests can serve as the basis 
for accurate decision-making regarding the need for liver transplantation in the 
setting of acute failure or in patients with chronic liver disease. The liver 
metabolic breath test relies on measuring exhaled (13) C tagged methacetin, 
which is metabolized only by the liver. Measuring this liver-specific substrate 
by means of molecular correlation spectroscopy is a rapid, non-invasive method 
for assessing liver function at the point-of-care. The (13) C methacetin breath 
test (MBT) is a powerful tool to aid clinical hepatologists in bedside 
decision-making. Our recent findings regarding the ability of point-of-care (13) 
C MBT to assess the hepatic functional reserve in patients with acute and 
chronic liver disease are reviewed along with suggested treatment algorithms for 
common liver disorders.