25.6 Calculation
To measure AST and ALT activities, pyruvate is used as the standard. In theoretical
terms, for AST assay oxaloacetate should be used as the standard, and pyruvate
should be used as the standard for ALT estimation. Since, the oxaloacetate formed
during AST estimation is unstable and gets converted into pyruvate immediately;
hence, pyruvate is preferred as the standard for AST estimation. Extrapolate pyru-
vate amount from graph and calculate activity. Enzyme activity is expressed as
IU. One IU of enzyme activity is equal to 1 mmol of pyruvate/oxaloacetate formed/
min/liter of serum at 37C. The amount of pyruvate formed equals to enzyme
activity. So, amount of pyruvate formed in m mol/min/l.
¼
ODof testðÞcontrol amount of standard mmolðÞ 1000
ODof standardsample volume mlðÞincubation time
¼xIU=L25.7 Clinical Significance...............................
The normal range of ALT is 3–40 IU/L and AST is 5–45 IU/L in serum. Normally,
the serum transaminase levels are low, but the extensive tissue damage enhances
their serum levels. The AST activity in serum is increased in myocardial infarction
after 20–36 h of onset, and hence measurement of AST is used in the diagnosis of
myocardial infarction. Increased activities are also observed in acute pancreatitis,
crushed muscle injuries, viral hepatitis, and other forms of liver diseases associated
with liver necrosis. Peak values of transaminases are seen between 7th and 12th days
of infection and return toward normal by 3rd week if recovery is uneventful.
ALT is generally higher than AST in infectious hepatitis and other inflammatory
conditions of liver or hepatic tissue damage. In such conditions, ALT/AST ratio
becomes greater than unity which is less than one in normal conditions. ALT is more
liver-specific enzyme than AST. AST levels also show increase in progressive
muscular dystrophy and dermatomyositis. ALT and AST levels are increased in
viral hepatitis (10–100 times of normal value). The course of liver damage in a
patient may be monitored by successive determination of serum AST and ALT
activities.
106 25 To Determine Alanine and Aspartate Transaminase Activity in Serum