Standard liver tests

Watch a video presentation of this article Watch the interview with the author The liver is the largest organ in the body and arguably the most important organ for protein production and detoxification, both of which are facilitated by a myriad of enzymes. Both the detection of enzymes released from liver cells and proteins produced by the liver and released into the blood can be used to analyze liver health. Standard liver tests (Tables 1 and 2) that assess injury to the liver include alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatases (APs). The excretory function of the liver can be estimated by bilirubin and the metabolic function of the liver by clotting tests and albumin. Tests that describe injury of the liver such as aminotransferases and AP have historically been mislabeled liver injury tests (LIT). In contrast, standard tests such as albumin, bilirubin, and prothrombin time are useful in evaluating liver function. The pattern of elevation of the different enzymes can be used to discriminate hepatocellular from cholestatic or mixed injury; AST and ALT are more elevated in patients with hepatocellular injury, whereas AP and γ-glutamyl transpeptidase (gGT) are more elevated in cholestatic injury. Normal values for laboratory results are defined as those found in 95% of a population. Thus, 2.5% of a population will be above and below the normal values, respectively. But being outside the normal does not immediately reflect illness; that is, a bilirubin level below normal has no clinical consequences. Contrarily, being within the normal value does not necessarily reflect a healthy state. In that regard it has been suggested to use an upper limit of 19 and 30 U/L for ALT for women and men, respectively,1 to reflect healthy values. This also fits the observed increased mortality in individuals with ALT values that are normal but above the healthy range.2 Thus, liver transaminases likely will be described as healthy (≤19 U/L for women and ≤30 U/L for men) and normal values (i.e., 5 seconds), which does not respond to parenteral vitamin K, is a poor prognostic sign.