Liver Diseases (General)

Evaluation of Liver Disease

Liver disease is classified according to the duration of abnormalities as either acute (<six months) or chronic (>six months). Evaluation of subjects with liver disease starts with basic laboratory blood tests. Elevation of molecules contained within the liver cell, the serum aminotransferases (AST and ALT) indicate injury to hepatocytes. Secondary to some insult, there is injury to the hepatocyte and these specific molecules can leak from the hepatocytes into the blood. The level of elevation in AST and ALT as well as their ratio may give some indication as to the possible inciting cause. For example, the ratio of blood AST to ALT is typically greater than 2 in alcoholic liver disease. In viral hepatitis, this ratio is characteristically less than one. Besides serum AST and ALT, other molecules can be studied to gain insight into liver disease. These include the enzyme alkaline phosphatase which is present in the liver, bone, and placenta. Elevations in serum alkaline phosphatase generally indicate obstruction of bile outflow from the liver, and concurrent elevation of alkaline phosphatase with elevation of liver enzymes suggests liver disease.

Besides the aforementioned tests of general injury to hepatic cells, other laboratory tests can help gain insight into the functional capacity of the liver. Bilirubin is a degradation product of hemoglobin that is carried in red blood cells. Breakdown and excretion of serum bilirubin involves processing in the liver, where broken-down bilirubin is processed (conjugated) and ultimately excreted. Elevated levels of unconjugated bilirubin can suggest a deficiency of the liver to take up and conjugate bilirubin, and elevated levels of conjugated bilirubin suggest deficiencies in excretion (possibly arising from mechanical obstruction).

Tests are also available to evaluate the synthetic capabilities of the liver. Albumin, a blood protein that is critical for binding molecules in the blood and maintaining its oncotic pressure, is synthesized in the liver. A decrease in serum concentration of albumin, although not entirely specific for liver disease, may be seen in chronic liver disease. Proteins involved with blood coagulation and hemostasis are processed in the liver, and tests such as the prothrombin time (PT) [Page 1024]and the corresponding international normalized ratio (INR) may be elevated in liver disease.

Aside from blood tests, evaluation of the liver also includes multiple imaging modalities that offer evaluation of the anatomy of the liver as well as the opportunity to possibly intervene when disease is present. Ultrasound of the liver is generally used to evaluate the biliary tree (predominant bile outflow tract of the liver) and evaluate for stones. Ultrasound can also detect large liver tumors and cysts. Advances in doppler ultrasonography can assess portal (liver-related) blood flow. Computerized tomography and magnetic resonance imaging are now used to evaluate the substance of the liver (parenchyma) to delineate intra-liver anatomy. Endoscopic retrograde cholangiopancreatography (ERCP) can be done by a gastroenterologist or hepatologist with advanced training—in this procedure an endoscope is advanced through the digestive system to ultimately visualize the biliary tree. If gallstones or other material is present causing liver outflow blockage, stone extraction or stenting can be done to relieve obstruction. Magnetic resonance cholangiopancreatography provides for visualization of the biliary tree; however, therapeutic intervention as with ERCP is not possible.

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