New methods for assessing liver function in infants and children.

Assessment of liver function in infants and children has traditionally relied on static indices of hepatic structure, cellular integrity, or function and are often based on the release of substances from damaged tissues. There has been a rapid development of dynamic tests based on the measurement of substances metabolized or cleared from blood by the liver. These tests, which have been touted to offer a more precise quantitative estimation of hepatic functional capacity, include the measurement of serum bile acids and the hepatic metabolism of xenobiotic compounds such as caffeine and lidocaine. Serum bile acid measurements appear to be reliable indicators of enterohepatic circulation and may be useful in screening for liver disease. It has been observed that caffeine metabolism is decreased in patients with various forms of liver disease in correlating with disease status. Caffeine has the advantage of being well tolerated when administered orally; the saliva level parallels the serum concentration, making a non-invasive test feasible. Lidocaine is metabolized by oxidative de-ethylation to monoethylglycinexylide (MEGX); analysis of MEGX by common laboratory instrumentation makes rapid evaluation of liver function possible. The MEGX values correlated were with pretransplant liver disease assessment. These tests are currently being evaluated at other centers and, if the initial studies are repeated, they offer the hope for reliable dynamic tests of hepatic function.