The AST/ALT ratio or De Ritis ratio is the
ratio between the
concentrations of the
enzymes
aspartate transaminase (AST) and
alanine transaminase, aka alanine aminotransferase (ALT) in the
blood of a
human or
animal. It is measured with a
blood test
A blood test is a laboratory analysis performed on a blood sample that is usually extracted from a vein in the arm using a hypodermic needle, or via fingerprick. Multiple tests for specific blood components, such as a glucose test or a cholester ...
and is sometimes useful in
medical diagnosis for
elevated transaminases 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 2:1 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
Hepatitis C is an infectious disease caused by the hepatitis C virus (HCV) that primarily affects the liver; it is a type of viral hepatitis. During the initial infection people often have mild or no symptoms. Occasionally a fever, dark urine, a ...
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.
When the AST is higher than ALT, a muscle source of these enzymes should be considered. For example, muscle inflammation due to
dermatomyositis may cause AST>ALT. This is a good reminder that AST and ALT are not good measures of
liver function when other sources may influence AST and/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). For example, intense exercise such as weight lifting can increase ALT to 50-200 U/L, and AST to 100-1000 U/L (and raise AST to about 4 times ALT) for the week following the exercise.
History
The ''De Ritis Ratio''
is named after
Fernando De Ritis, who performed analysis on transaminases in 1957.
Mechanism
The proportion of AST to ALT in hepatocytes is approximately 2.5:1, but because AST is removed from serum by the
liver sinusoidal cells twice as quickly (serum
half-life t
1/2 = 18 hr) compared to ALT (t
1/2 = 36 hr), so the resulting serum levels of AST and ALT are about equal in healthy individuals, resulting in a normal AST/ALT ratio of approximately 1.
An AST/ALT ratio >5 necessarily involves extrahepatic tissue, as death of hepatocytes alone would produce an AST/ALT ratio no greater than 2.5. Because the primary cause is extrahepatic, there is typically an isolated elevated AST, with no change in ALT. Common causes include bone disease, pregnancy, chronic renal failure, lymphoma, and congestive heart failure.
When hepatocellular death is increased beyond the usual "background" levels, the serum levels of AST compared to ALT tend to reflect the cellular proportions, yielding AST that is over twice as prevalent as ALT (AST/ALT >2) in conditions with chronic, constant hepatocyte damage (such as alcoholic hepatitis, hepatocellular carcinoma) and during early-stage acute liver damage (such as viral hepatitis).
In late-stage acute liver damage, the body has had adequate time to clear AST, but not ALT, often resulting in an AST/ALT <1. Since testing typically occurs late in acute viral hepatitis, it is conventionally associated with an AST/ALT ratio <1, even though early in the disease AST/ALT ratio is often elevated. As the acute liver damage resolves, the body has more time to clear ALT, so in the absence of chronic liver disease, the AST/ALT ratio gradually returns to baseline levels.
See also
*
Aspartate transaminase
*
Alanine transaminase
*
Liver function tests
*
Elevated transaminases
References
{{DEFAULTSORT:AST ALT ratio
Liver function tests