What Is LDH?
Lactate dehydrogenase (LDH) is an enzyme found in almost every cell in the body. When cells are damaged or destroyed, LDH leaks into the bloodstream. Because it's in so many tissues, an elevated LDH indicates cellular damage but does not pinpoint the source — it must be interpreted alongside other tests.
Normal LDH Range
| Group | Normal LDH Range |
|---|---|
| Adults | 140–280 U/L |
| Children | Higher ranges apply by age |
Causes of High LDH by Organ/Condition
| Source | Examples |
|---|---|
| Heart | Heart attack (myocardial infarction — historically, now replaced by troponin) |
| Liver | Hepatitis, cirrhosis, fatty liver |
| Lungs | Pulmonary embolism, pneumonia, COVID-19 |
| Blood | Haemolytic anaemia, pernicious anaemia (B12 deficiency) |
| Muscle | Rhabdomyolysis, muscular dystrophy |
| Cancer | Leukaemia, lymphoma — high LDH is a marker of tumour burden |
| Kidney | Renal infarction |
LDH in Cancer Monitoring
In testicular cancer, lymphoma and melanoma, LDH is used as a tumour marker — elevated at diagnosis and tracked to assess treatment response. Very high levels suggest aggressive or widespread disease.
FAQs
Can haemolysed blood samples cause false high LDH?
Yes — if the blood sample is poorly handled and red cells break, LDH will be falsely elevated. A repeat sample is often needed.
Is LDH the same as troponin for heart attack?
No — LDH was historically used for heart damage but is non-specific. Troponin is now the gold standard cardiac marker.
Is fasting required?
No fasting needed.
Medical Disclaimer: Elevated LDH requires interpretation alongside clinical symptoms and organ-specific tests to identify the source of damage.