In the case of a myocardial infarction (MI), cardiac muscle cells get damaged, releasing specific enzymes into the bloodstream.
CKMB (Creatine Kinase-MB fraction) is one of the earliest markers for myocardial injury.
It starts rising within 2 to 4 hours of infarction, peaks around 12 to 24 hours, and returns to normal within 48 to 72 hours.
LDH (Lactate Dehydrogenase) also rises but later, usually after 24 to 48 hours.
SGPT (ALT) is mainly a liver enzyme and not specific for MI.
Acid phosphatase is related to prostate and other tissues but not cardiac muscle.
Therefore, CKMB is the enzyme elevated in the first 2 hours of MI.