Lactic dehydrogenase (LDH) is an enzyme used as a marker of cellular damage/necrosis, that catalyzes the transformation of lactate to pyruvate. It is an enzyme expressed in different cell types, but it is expressed as different isoenzymes.

There are 5 different cytoplasmic isoenzymes expressed in different tissues:

- LDH1 mainly in the myocardium;

- LDH2 and LDH3 mainly in the lung;

- LDH4 not majorly produced by a specific tissue;

- LDH5 expressed primarily in the liver.

For a myocardial infarction, the LDH1 assay can be used as a marker, which increases. If, on the other hand, the suspicion is for liver necrosis, LDH5 can be used. Therefore, by measuring the amount of blood of a particular isoenzyme, it is possible to assess whether there has actually been a death by necrosis in that district where it is most expressed.

The increase in LDH, to be significant, requires 10-12h. So, you take a sample at the time of admission and one after 10-12h, and if there is an increase in LDH there is an indication in favor of necrosis.

However, the increase of these enzymes occurs also in other pathological conditions, such as megaloblastic anemia, muscle injury and renal infarction. In fact, the result must be added to the history and other evaluations.

Normal values: 80 and 300 mU/ml.