The most commonly used indicators of healthy liver function include the enzymes aspartate aminotransferase, or AST, and alanine aminotransferase, or ALT. When liver injury occurs, these enzymes flood the bloodstream. Blood tests that show high levels of AST and ALT commonly but not always indicate some type of liver injury or damage. Normal values for AST are 5 to 40 units per liter of blood, and normal ALT values range from 7 to 56 units per liter of blood.
Fatty Liver
"Medical Surgical Nursing" describes fatty liver as the accumulation of triglycerides and other fats in the liver cells. When the amount of fat in the liver exceeds approximately 40 percent, the liver begins to malfunction and becomes damaged. According to the American Academy of Family Physicians, obese patients exhibit higher levels of ALT and AST. These levels have been shown to decrease with weight loss.
Alcoholic Cirrhosis and Hepatitis
Alcoholic cirrhosis occurs due to the habitual use of large amounts of alcohol and causes elevations in liver enzymes. Hepatitis, a chronic viral infection of the liver, also causes elevations in liver function tests due to the damage and death to liver cells. According to Dr. David E. Johnston of the University of New Mexico School of Medicine, patients with hepatitis C often show normal levels of ALT. He also states that these chronic diseases often only show slight elevations of ALT and AST.
Drugs
Medications commonly cause acute injury to the liver and mildly increase AST and ALT levels. The American Academy of Family Physicians lists Tylenol, Cardarone, Diflucan, Tegretol, Augmentin, Micornase, Heparin, Nizoral, Dilantin, Desyrel and isoniazid as medications that commonly cause elevations of liver functions. Herbs such as kava, ephedra, senna, and vitamin A also cause elevations of ALT and AST.
Other Disorders
Many other disorders cause elevations of ALT and AST, including muscle injury. These enzymes are also found in muscle and when muscles become strained or damaged, ALT and AST release into the bloodstream. Other disorders that cause liver functions to elevate include cancer, hemochromatosis, and iron or copper deficiency.
References
- American Academy of Family Physicians: Special Considerations in Interpreting Liver Function Tests
- American Academy of Family Physicians: Mildly Elevated Liver Transaminase Levels in the Asymptomatic Patient
- "Medical Surgical Nursing"; D. Ignatavicius, MSN, L. Workman, Ph.D.; 2002
