LDH-2 is the second isoenzyme of lactate dehydrogenase and is found predominantly in cardiac muscle and red blood cells. In a normal blood sample, LDH-2 is the most abundant isoenzyme, exceeding LDH-1. An elevated LDH-1 relative to LDH-2 (LDH-1 greater than LDH-2) — known as a 'flipped' LDH pattern — is a classic indicator of myocardial infarction or haemolysis.
While cardiac troponin has largely superseded LDH isoenzymes in the acute setting, LDH-2 testing remains useful when assessing haemolytic conditions — where increased red blood cell destruction releases LDH-2 into the bloodstream — and in haematological malignancies where red blood cell turnover is elevated.
FAQs
Why is LDH-2 normally higher than LDH-1?
In healthy individuals, LDH-2 is the most abundant circulating isoenzyme, reflecting its distribution in cardiac and red cell tissue under normal turnover. Disease states selectively release LDH-1 from damaged cardiac or haemolysing red cells, inverting this normal ratio.
What does a normal LDH-2:LDH-1 ratio mean?
A normal ratio (LDH-2 > LDH-1) is reassuring against significant acute cardiac injury or haemolysis. It is one component of LDH isoenzyme analysis interpreted alongside clinical findings.
Is LDH-2 testing done routinely?
No. LDH isoenzyme analysis is ordered specifically when characterising the source of elevated total LDH. It is not part of routine blood panels.
Can haemolysis in the blood sample affect LDH-2?
Yes. Haemolysis of the blood sample itself (from poor collection technique) releases red cell LDH including LDH-1 and LDH-2 into the sample, causing artificial elevations that do not reflect in vivo tissue injury. Haemolysed samples may need to be repeated.
