Quantitative Tests

Many complex techniques are available for quantitatively assessing specific hepatocellular functions. For example, measuring the clearance of substances that the liver avidly extracts—such as bromsulphalein, indocyanine green (ICG), and rose bengal—may provide information about the mass of working hepatocytes. ^[217] However, the body may retain such substances without losing any hepatocytes. Retention may reflect decreases in hepatic blood flow or abnormalities in hepatocellular uptake, intracellular binding, metabolic transformation, or hepatobiliary excretion of these substances. Various tests provide a measure of hepatic drug metabolizing capacity. Included among these tests are galactose elimination capacity, aminopyrine breath test (ABT), antipyrine clearance, monoethylglycinexylidide (MEGX), and caffeine clearance.^{[190] [218] [219] [220] [221] [222] [223]} MEGX, a lidocaine metabolite, is measured in a blood sample taken 15 minutes after an intravenous injection of lidocaine (1 mg/kg).

Noninvasive methods can be used to determine caffeine clearance. This involves sequential measurements of caffeine metabolites in saliva for up to 24 hours after an oral dose of caffeine (150–300 mg). Such quantitative tests have been mainly limited to research centers. Generally, they are more expensive, invasive, or time-consuming than conventional biochemical tests, without compelling evidence of being superior, either diagnostically or prognostically. Thus, the role of quantitative tests in managing patients with liver disease remains to be determined.