LDHserum

LDHserum refers to the activity of lactate dehydrogenase measured in serum. Lactate dehydrogenase is a cytosolic enzyme that catalyzes the interconversion of lactate to pyruvate while oxidizing NADH to NAD+. It is abundant in many tissues, so serum LDH levels rise with tissue damage or turnover and can serve as a general marker of cellular injury.

Serum LDH is measured by enzymatic activity assays that monitor the rate of NADH oxidation or the coupled formation of NAD+. Many laboratories report total LDH activity and, in some cases, LDH isoenzymes (LDH-1 to LDH-5) to help localize injury. Isoenzyme patterns reflect tissue distribution: LDH-1 is abundant in heart and red blood cells, while LDH-5 is more common in liver and skeletal muscle.

Elevated LDH is not specific to a single disease. It can accompany myocardial infarction, liver disease, hemolysis, pancreatitis, muscle injury, or certain cancers. A rising or falling LDH trend, in conjunction with other tests, may aid assessment but should not be used alone for diagnosis. Isoenzyme patterns can sometimes aid localization of tissue injury.

Normal reference ranges vary by laboratory and method, typically about 140 to 280 U/L in adults, but values may differ. Preanalytical factors such as hemolysis during sample collection can falsely raise LDH. Other conditions, age, and medications can influence results, so LDHserum results are interpreted in the clinical context alongside other biomarkers.