LDH-1 is the first and most cardiac-specific isoenzyme of lactate dehydrogenase, found predominantly in the heart muscle and red blood cells. In a normal blood sample, LDH-2 is the dominant isoenzyme. Following a myocardial infarction, LDH-1 rises significantly — and when LDH-1 exceeds LDH-2 (the 'flipped' LDH pattern), it is a highly suggestive finding for cardiac damage.
While high-sensitivity troponin has become the primary cardiac biomarker in emergency settings, LDH-1 retains clinical utility in situations where troponin measurement is unavailable, in late presentations after myocardial infarction (when troponin may have normalised but LDH remains elevated), and in the assessment of haemolytic conditions where red blood cell destruction also releases LDH-1.
FAQs
What is the flipped LDH pattern?
Normally LDH-2 is the most abundant isoenzyme (LDH-2 > LDH-1). A flipped pattern, where LDH-1 exceeds LDH-2, occurs when cardiac or red cell damage specifically elevates LDH-1. It is a classic late indicator of myocardial infarction or haemolytic anaemia.
Has troponin replaced LDH-1?
For acute cardiac diagnosis in emergency settings, high-sensitivity troponin has largely superseded LDH-1 due to earlier detection and greater cardiac specificity. LDH-1 retains utility in late presentations and haemolysis assessment.
Which anaemias cause elevated LDH-1?
Haemolytic anaemia (any cause), megaloblastic anaemia (B12 or folate deficiency causing intramedullary haemolysis), and sickle cell disease all characteristically elevate LDH-1 through red blood cell destruction.
Is LDH-1 testing widely available?
LDH isoenzyme analysis including LDH-1 is available in most pathology laboratories but is requested specifically when the source of elevated total LDH needs to be characterised, rather than as a routine test.
