LDH-5 is the fifth isoenzyme of lactate dehydrogenase, found in highest concentrations in the liver and skeletal muscle. Elevation of LDH-5 specifically suggests damage to liver cells or skeletal muscle, and helps differentiate the source of an elevated total LDH result.
In liver disease, LDH-5 rises alongside ALT and AST, providing confirmatory evidence of hepatocellular injury. In skeletal muscle conditions such as rhabdomyolysis, myopathy, or intense exercise, LDH-5 rises alongside CK and myoglobin. Distinguishing liver from muscle injury is important clinically and LDH isoenzyme testing provides this specificity.
FAQs
How do you tell if elevated LDH-5 is from liver or muscle?
ALT measurement helps distinguish them. Significantly elevated ALT alongside LDH-5 points to a hepatic source. Markedly elevated CK alongside LDH-5 points to skeletal muscle injury. Both can coexist.
Can exercise raise LDH-5?
Yes. Intense exercise causes skeletal muscle cell damage, releasing LDH-5 alongside CK. After a heavy training session, endurance event, or rhabdomyolysis, LDH-5 can be substantially elevated for several days.
Is LDH-5 routinely tested?
No. LDH isoenzyme analysis including LDH-5 is specifically ordered to characterise the source of elevated total LDH. ALT and CK provide more direct and readily available measures of liver and muscle injury respectively.
What liver conditions cause the highest LDH-5?
Ischaemic hepatitis (shock liver from acute circulatory failure) causes extremely high LDH-5, often disproportionately elevated compared to ALT. Viral hepatitis, toxic hepatitis, and hepatic ischaemia from other causes also markedly elevate LDH-5.
