Acute hepatocellular injury and chronic hepatocellular or cholestatic liver injury can lead to an impairment of liver function (liver failure). However, liver failure does not occur unless there is extensive liver injury. Therefore abnormal values generally imply advanced liver disease. The common tests that assess liver synthetic function are albumin and prothrombin time or INR.

Albumin

Albumin is the most abundant protein produced by the liver. Serum albumin is low in liver failure. Because of its long half-life (2-3 weeks), albumin is most useful in the assessment of chronic liver failure. Albumin production can be reduced in many non-hepatic causes such as malnutrition, chronic kidney disease, and chronic inflammatory diseases. Serum albumin can also be low when its excretion is increased (albuminuria, malabsoprtion).

Prothrombin Time (PT) or INR (International Normalized Ratio)

The liver produces the majority of coagulation proteins needed in blood clotting cascade. Severe liver injury leads to reduction of liver synthesis of clotting factors and consequently prolonged PT or an increased INR, which is a method to homogenize PT level reporting across the world. Because clotting factors have shorter half-life than albumin, PT (or INR) is useful in assessing the presence of both acute and chronic liver failure. Similar to albumin, however, abnormal PT (or INR) may be due other non-hepatic causes such as vitamin K deficiency, malabsorption and genetic clotting disorders. The increased PT secondary to liver failure will not improve with vitamin K repletion. Patients who take coumadin will have an elevated INR which does not imply poor liver function.