LDH (Lactose dehyrogenase) is a biomarker for tissue injury or cell lysis anywhere in the body. Typically it was used for heart damage during myocardial infarction where it was a cardiac necrosis marker. It is also possible that it is a liver disease biomarker that shows liver injury by itself or in cancer metastasis. In lung fibrosis, it is a sign of lung involvement or unrelated to fibrosis, it points to a lung tissue. It is also used as injury in any other organ injury such as kidney, muscle, pancreas or even brain. In hematologic disorders it may also be involved.
Thus LDH is very non-specific. For a clinician to interpret the LDH increase they need to combine it with something else, such as troponin for the heart and ALT/AST for the liver. The normal range is 140-333 U/L and any increase needs to be carefully analyzed for inflammation or tissue damage. However, it is possible to show an increase due to some technical reasons too.
Few examples where elevated LDH may not be an issue may be a defective blood draw that causes RBC lysis, freeze-thaw of sample, improper storage or extremely high WBC count. Sometimes, acute exercise, or manual labor, or pregnancy can cause an elevation. However, the clinician would also look out for unusual conditions such as hypothyroidism, Cushing syndrome, anorexia, Cancer cachexia or any other conditions.
To help determine the involvement, many LDH isozymes can be tissue specific. LDH1: heart and RBC, LDH2: WBC, LDH3: lungs, LDH4, Kidney, placenta, pancreas LDH5: liver and skeletal muscle. These are not used as often but can be used.
In cancer, metabolism shifts towards Warburg effect favoring glycolysis and that increases total LDH and alters isozyme balance (LDH-a/LDH5). LDH5 helps push pyruvate towards lactate and regenerates NAD so glycolysis continues at high speed and acidifies the tumor microenvironment by lactate production.
Sometimes it helps identify which tissue isoforms dominate tells you about the tumor and its metabolic activity. Sometimes, rising LDH pattern during or after treatment can suggest progression and falling may reflect good response, however, this needs to be carefully analyzed since this could be non-specific.
