- Overview of ALT and AST Liver Enzymes
- AST/ALT ratio
- What is the Real Function of the Liver Function Tests?
Overview of ALT and AST Liver Enzymes
Serum AST and ALTand season episode and you
Liver enzymes are commonly used in the evaluation of patients with a range of diseases. However, knowledge of enzyme ratios and pattern recognition allow much more information to be derived from these simple tests. However, much more may be interpreted from these assays with knowledge of enzyme ratios and pattern recognition. This paper offers an insight to generalists of how to yield greater information from this simple test. A basic understanding of each enzyme is fundamental to interpreting the meaning of their titre. The basic pathophysiology of each is delineated in Table 1. The mitochondrial isoenzyme is produced in hepatocytes and reacts to membrane stresses in a similar way to ALT.
Liver enzymes are substances produced by the liver that can be measured with a blood test. Any elevation in an enzyme level may be a sign of a liver problem, and aspartate aminotransferase AST and alanine aminotransferase ALT are two of the enzymes central to such an investigation. Aminotransferases are chemicals that the liver uses to make glycogen. Glycogen is the stored form of glucose, a sugar that the body uses for energy. Any glucose not immediately used will be converted into glycogen and stored in cells for future use.
Laboratory assessment of the patient with suspected or clinically obvious liver disease is context dependent. For example, the acutely ill jaundiced patient with a history of prolonged alcohol ingestion requires a different laboratory assessment than the well patient in whom one or more standard liver test results are discovered to be abnormal during routine testing. Additionally, the sequence of liver tests depends heavily on the questions being asked. If it is to determine whether this well person whose brother was recently diagnosed with hemochromatosis also has this genetic disease, then a series of tests will be initiated to detect the possibility of iron overload. If it is to determine whether this spouse has been infected with hepatitis B, then blood tests related to hepatitis B will be required. Thus generic algorithms for the evaluation of liver disease need to be considered skeptically.
Tests indicative of: 1 liver inflammation: ALT alanine aminotransferase and AST aspartate aminotransferase ; 2 cholestasis or biliary obstruction: bilirubin total includes both direct and indirect bilirubin , ALP alkaline phosphatase and GGT gamma-glutamyltransferase ; and 3 synthetic function: albumin and PT prothrombin time. Used to assess the presence of liver fibrosis. PT, reported as the INR, measured from citrated whole blood: 1 full blue top, mixed gently. Symptoms suggestive of liver disease: jaundice, dark urine, or light-colored bowel movements, loss of appetite, fatigue, vomiting of blood, bloody or black bowel movements, swelling or pain in the abdomen, unusual weight changes. Signs suggestive of liver disease: hepatomegaly, ascites Exposure to medications associated with liver damage e. HMG Co-A reductase inhibitors, thiazolidinediones , contact with people that have viral hepatitis, excessive alcohol consumption. Presence of additional comorbid conditions associated with liver disease among persons with diabetes: extreme obesity, hypertriglyceridemia, alcohol use To monitor response to treatment or track course of disease in patients with liver disease.
What is the Real Function of the Liver Function Tests?
Alanine aminotranferease ALT and aspartate aminotransferase AST are enzymes located in liver cells that leak out into the general circulation when liver cells are injured. These two transaminase enzymes may be reported on lab slips with both their new names and previous names or by their newer names only. ALT and AST are present in highest concentrations in cells from the liver, heart, skeletal muscles, and red blood cells. Patients whose LFTs show a predominant rise in the transaminases have liver diseases that are characterized by hepatocellular damage. ALT is found predominately in the liver, with lesser quantities found in the kidneys, heart, and skeletal muscle. As a result, the ALT is a more specific indicator of liver inflammation than the AST, as the AST may also be elevated in diseases affecting other organs, such as the heart or muscles. The AST is also elevated after a myocardial infarction, and during acute pancreatitis, acute hemolytic anemia, severe burns, acute renal disease, musculoskeletal diseases, and trauma.
It is measured with a blood test and is sometimes useful in medical diagnosis to differentiate between causes of liver damage, or hepatotoxicity. Most causes of liver cell injury are associated with a greater increase in ALT than AST; however, an AST to ALT ratio of or greater is suggestive of alcoholic liver disease, particularly in the setting of an elevated gamma-glutamyl transferase. The AST to ALT ratio can also occasionally be elevated in a liver disease pattern in patients with nonalcoholic steatohepatitis , and it is frequently elevated in an alcoholic liver disease pattern in patients with hepatitis C who have developed cirrhosis. In addition, patients with Wilson's disease or cirrhosis due to viral hepatitis may have an AST that is greater than the ALT, though the ratio typically is not greater than two. This is a good reminder that AST and ALT are not good measures of liver function when other sources may increase AST or ALT, because they do not reliably reflect the synthetic ability of the liver, and they may come from tissues other than liver such as muscle [ citation needed ]. It is also known as the "De Ritis Ratio",   named after Fernando De Ritis , who performed analysis on transaminases in From Wikipedia, the free encyclopedia.