Tests of haemolysis - lactate dehydrogenase (LDH)

Role

Serum LDH rises in haemolysis, reflecting release of this intracellular enzyme from destroyed red cells - one of the most sensitive components of the standard haemolysis screen, though notably non-specific given LDH's presence in many other tissues
A standard, routinely available test used alongside bilirubin, haptoglobin, and reticulocyte count to confirm haemolysis

LDH is present in high concentration within red cells (and many other cell types) - red cell destruction (whether intravascular or extravascular haemolysis) releases LDH into the plasma, causing a measurable rise proportional to the degree of cell destruction

LDH is sensitive but highly non-specific - elevated in many conditions beyond haemolysis (tissue damage generally, malignancy including lymphoma, myocardial infarction, hepatic disease, muscle injury) - an isolated raised LDH without other supporting haemolysis features (raised bilirubin, low haptoglobin, raised reticulocyte count, and blood film findings) should not be interpreted as confirming haemolysis alone
The combination of raised LDH + low haptoglobin is a strong, relatively specific combination for haemolysis, since haptoglobin's fall (from binding and clearing free haemoglobin) is a more haemolysis-specific finding than LDH elevation alone

LDH is used both to support the initial diagnosis of haemolysis and, in some settings (e.g. monitoring known haemolytic conditions, or in lymphoma as a marker of disease burden/prognosis in a completely different context), to track disease activity/burden over time

Haemolytic anaemia (all causes), lymphoma (LDH as a prognostic marker in a distinct, non-haemolytic context), myocardial infarction, tissue injury generally

LDH's lack of specificity means it should never be interpreted as diagnostic of haemolysis in isolation - the full haemolysis panel (bilirubin, haptoglobin, reticulocyte count, blood film for schistocytes/spherocytes) together, in the correct clinical context, is what establishes the diagnosis

5 more sections, plus exam facts

Premium unlocks every note across every specialty, and the full exam fact library behind it.