Three days after the onset of myocardial infarction which enzyme level has the best predictive value?

 # Three days after the onset of myocardial infarction which enzyme level has the best predictive value?

A. Serum CPK

B. Serum LDH

C. Serum SGOT

D. Serum SGPT

The correct answer is B. Serum LDH

Lactate dehydrogenase (LDH) levels rise 12-24 hours after myocardial infarction (MI), peak at 48-72 hours (around day 3), and remain elevated for 7-14 days, providing the highest diagnostic sensitivity and predictive value for confirming MI at this late stage. In contrast, creatine phosphokinase (CPK) peaks early (12-24 hours) and normalizes by day 3, making it less useful then; serum glutamic-oxaloacetic transaminase (SGOT/AST) peaks at 24-48 hours and declines by day 3-4; and serum glutamic-pyruvic transaminase (SGPT/ALT) is primarily liver-specific with minimal cardiac relevance. The LDH-1 isoenzyme is particularly specific for cardiac tissue damage.