LACTATE DEHYDROGENASE (LD) - serum

LACTATE DEHYDROGENASE (LD) - serum

Application: Diagnosis of myocardial infarction , esp. >48 hours after onset of chest pain.


Explanation: LD becomes elevated 24-48 hrs post-infarction. It peaks between 48-72 hrs, and slowly falls to normal between 5-10 days. LD tends to parallel AST, at twice the time. LD is more sensitive than AST and is elevated  even in infarcts that show no AST abnormality. In acute liver damage LD is not as sensitive as AST. In the acutely and chronically passively congested liver, LD is most often normal or minimally elevated.

   LD is actually a group of enzymes. Individual enzymes or isoenzymes make up “total LD”. LDH-1 is found mainly in RBC, heart, and kidney, as is LDH-2. LDH-3 is in lung tissue, while LDH-5 is mainly in liver tissue. Skeletal muscle has significant representation in all fractions although higher in LDH-5. LD isoenzyme fractionation is a method of diagnosing myocardial infarction when liver damage is suspected to contribute to the total LD increase. For example, in liver damage without MI, LDH-1 is normal and most LD increase is due to fraction 5. If MI and liver damage coexist, fractions 1 & 5 are both elevated. Normally, LDH-2 is slightly more elevated than LDH-1. Classically, in a myocardial infarction LDH-1 is markedly elevated, more so than LDH-2; thus, there is inversion of the usual pattern, called "flip" isoenzyme pattern.

Specimen: 7-10 ml blood in red-top tube.


Reference Interval:
            100-190 U/L

Isoenzymes:
            LDH-1: 17-27%
            LDH-2: 27-37%
            LDH-3: 18-25%
            LDH-4: 3-8%
            LDH-5: 0-5%