What is ALT?
Alanine aminotransferase (ALT, also known as SGPT) is one of the most widely tested liver enzymes. The other one is aspartate aminotransferase (AST or SGOT). In healthy persons, these liver enzymes are predominantly contained within liver cells and to a lesser degree in the muscle cells. When the liver is injured or damaged, liver cells spill these enzymes into the blood stream, resulting in elevated levels of AST and ALT in the blood and indicating liver diseases. There are also other enzymes found in the liver, including alkaline phosphatase, gamma-glutamyl transpeptidase (GGT) and 5' nucleotidase. ALT and the other liver enzyme tests are used to assess liver damages from hepatitis, infection, cirrhosis, liver cancer, or other liver diseases. Other factors including medicines, age, gender, diet, body weight, and geographical location can affect ALT results.
The normal range for ALT in blood has been an issue of debate and does vary depending on testing laboratories or medical organizations and the purpose of the assay. In healthy individuals, blood ALT levels can fluctuate 10 to 30% from one day to the next and can fluctuate 45% during a single day, with highest levels observed in the afternoon and lowest level at night. Our test population has a median value of 16 units per liter (U/L) in adults who do not have known liver diseases. This is comparable to the median value of 11 U/L for women and 13 U/L for men in a published report. For disease diagnosis purpose, the cutoff is usually set at a very high value, 63 U/L; however, ALT should be maintained in an optimum range for health management purpose. We recommend an optimum blood ALT level between 14 and 33 U/L.
Elevated ALT increases mortality risk, not only in liver disease but also in non-liver-related ailments, particularly cardiovascular disease. Mortality jumps up by 60% -80% when ALT is twice beyond the higher of the normal range.
Whereas doctors pay more attention to elevated ALT values, lower ALT in blood has been shown to be associated with lower total-body muscle mass, lower baseline fitness, increased frailty and risk of mortality in elderlies and increased risk of all-cause mortality in healthy, middle-aged and elder people. The association between ALT and mortality is inconsistent and seems particularly susceptible to age. ALT is more valuable in predicting mortality in the older population. Extremely low ALT levels appear to indicate a higher all-cause, cardiovascular-related, and cancer-related mortality.
Analysis of over 10,000 nondiabetic subjects of age 21-84 years suggested an upward surge from 21 to 64 years and a discernible steady downward decline around 65 years of age.
What are the risk factors for abnormal ALT?
Elevated ALT levels are indications of abnormal live function or damage, including non-alcoholic fatty liver disease (NAFLD), hepatitis, alcohol-related liver disease, bile duct disorders, autoimmune live disease, drug and medicine (aspirin, Tylenol, Advil, Motrin and others), and other etiology such as smoking, high cholesterol, overweight, sedent lifestyle and environmental toxins.
Causes for low ALT are not very well known. Malnutrition could be a risk factor for low ALT.
Intervention tips to lower ALT levels
If your ALT test is outside of the normal range, you should consult your doctor who may recommend a confirmatory test and/or additional tests to find out the exact cause for the abnormal finding. There also preventive actions you can take to keep your liver healthy and your ALT level within healthy range. These may include:
Intervention tips to raise abnormally low ALT levels
There are no known remedies for rectifying lower than normal levels of ALT at this time because limited research has been devoted to the harmful effect of low ALT in the blood on health and mortality. Follow general guidelines for healthy lifestyle including balanced diet and exercise.
Further reading