Lactate dehydrogenase (LD) has 5 isoenzymes - LD1, LD2, LD3, LD4 and LD5.

Normally in serum the amount of LD1 is less than LD2, so that the ratio of LD1-to-LD2 is less than 1.00.


Increases in LD1 and LD2 can be seen in acute myocardial injury, hemolytic anemias or renal disease. Sometimes these increases show a "flip" in the relationship between LD1 and LD2, so that LD1 exceeds LD2, resulting in the LD1-to-LD2 ratio being greater than 1.00. This "flip" is seen more often in acute myocardial injury; however, it can less frequently be seen in hemolytic anemia and renal disease.



Timing After AMI

earliest increase

12 - 24 hours

peak level

55 - 60 hours

return to normal

10 - 14 days


A 48 hour specimen (2 days) is typically drawn to detect the increase.



• not useful for early recognition of acute myocardial injury

• troponin useful for late diagnosis of myocardial injury


Clinical utility:

• sensitivity: 61-90%

• specificity: 94-99%


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