What is Considered High AST and ALT Levels?
Marked Elevation of Aminotransferases
When the alanine aminotransferase (ALT) is elevated 10 or more times the upper limit of reference (values lower than 40 U/l), it can be diagnosed the existence of acute liver injury, and in these cases should be initiated immediately the etiological study. More than 90% of cases are caused by acute viral hepatitis.
The diagnosis of an acute hepatitis due to Hepatitis A Virus or Hepatitis B Virus does not usually present difficulties, but the diagnosis of an acute hepatitis due to Hepatitis C Virus is more complex because the positivity of the anti-HCV or of the HCV RNA does not discriminate between acute or chronic infection. The diagnosis of acute infection will be based on the presence of a clinical presentation of acute liver damage, the exclusion of other acute viral hepatitis and the presence of HCV RNA with anti-VH C negative or seroconversion of anti-HCV in 1 -3 months.
When values of aspartate aminotransferase (AST) exceed 100 times the upper limit of reference, hepatic ischemia or hypoxia and toxic or pharmacological hepatitis are the responsible cause in more than 90% of cases.
In a recent study, biliary obstruction was the cause of an elevation ≥ 10 times the transaminase values in 25% of cases.
Mild or Moderate Elevation of Aminotransferases
The chronic hepatic lesion is usually asymptomatic or paucisymptomatic (causing few symptoms) and generates an elevation of aminotransferases less than 10 times the upper limit of reference. Chronicity is defined by the persistence of the enzymatic elevation observed at least twice during a minimum period of 6 months.
Therefore, the initial step in the diagnostic evaluation of mild or moderate hypertransaminasemia is the repetition of the analysis, which will confirm, if necessary, the existence of the abnormality and define it as chronic, and then the etiological evaluation will begin. Some experts recommend, however, start the etiological study after confirming enzymatic elevation in a shorter period (between 2 and 4 weeks). The diagnostic systematics to be followed is usually structured in a sequence in which progress is made until the etiological diagnosis of hypertransaminasemia is obtained.
However, the order of the steps to follow can be altered depending on the clinical context in which the finding of the analytical alteration occurs and the data provided by the initial clinical history.
The initial clinical assessment should be aimed at identifying risk factors for viral chronic hepatitis (previous transfusion of blood products, parenteral drug abuse, risky sexual behaviors, tattoos, piercing, etc), excessive alcohol consumption, treatment with potentially hepatotoxic drugs, family history of liver disease and associated diseases (obesity, diabetes, hyperlipidemia, autoimmune diseases, etc.).
In USA, the most frequent chronic viral hepatitis is caused by HCV. Its diagnosis is based on the detection of anti-HCV antibodies by means of ELISA, so that in a patient with hypertransaminasemia and risk factors for HCV infection it is not necessary to use other confirmation techniques, however the viral RNA must be determined in serum by PCR in those cases in which it is valued to perform treatment and when it is necessary to confirm the diagnosis of active infection. Chronic liver disease due to HBV is diagnosed by the positivity of HBsAg and total anti-HBc, with H BeAg, anti-HBe and viral DNA subsequently being determined to investigate the presence of replication.
Excessive alcohol consumption is usually referred by the patient, but on many occasions it is minimized or hidden. The AST/ALT ratio is a data to consider if this etiology is suspected since 90% of the subjects with an AST / ALT ratio> 2 present histological data of alcoholic liver disease.
In the diagnostic study of the patient with hypertransaminasemia is especially relevant to follow a pre-established system that allows determining with sufficient precision the cause, avoiding in turn, the performance of unnecessary examinations.