LDH-3 is the third isoenzyme of lactate dehydrogenase, found predominantly in the lungs, lymphoid tissue, platelets, pancreas, and spleen. It is the isoenzyme most closely associated with lung and lymphoid tissue injury, making it the most relevant LDH isoenzyme in haematological malignancies and pulmonary conditions.
In haematological cancers such as lymphoma and leukaemia, LDH-3 (and LDH-4) are typically the most elevated isoenzymes because lymphoid cells and the lymph nodes, spleen, and bone marrow are involved. LDH-3 elevation also occurs in lung disease, pulmonary embolism, and platelet disorders.
FAQs
Why is LDH-3 elevated in lymphoma?
Lymphoma involves proliferation of lymphoid cells, which are rich in LDH-3. As tumour cells are destroyed by the immune system, chemotherapy, or due to poor perfusion, they release LDH-3 into the bloodstream. LDH level and isoenzyme pattern correlate with tumour burden.
Can pulmonary embolism cause elevated LDH-3?
Yes. Lung ischaemia from a pulmonary embolism releases LDH-3 from pulmonary endothelial and epithelial cells. The classic triad of elevated LDH, low albumin, and normal bilirubin was historically used in PE assessment but has been superseded by CT pulmonary angiography.
Is LDH-3 measured routinely?
No. LDH isoenzyme analysis is specifically ordered to characterise the source of elevated total LDH. It is not part of routine panels but is available in specialist pathology laboratories.
What other conditions elevate LDH-3?
Infectious mononucleosis causes marked LDH-3 elevation from lymphoid proliferation. Platelet disorders and pancreatitis can also contribute to elevated LDH-3 as part of their broader LDH isoenzyme profile.
