Chemistry
Cardiac related
Lactate dehydrogenase (LDH)

Author: Larry Bernstein, M.D. (see Authors page)

Revised: 2 February 2016, last major update December 2010

Copyright: (c) 2002-2016, PathologyOutlines.com, Inc.

PubMed Search: Lactate dehydrogenase [title]
Cite this page: Lactate dehydrogenase (LDH). PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/chemistrycardiaclactatedehydrogenase.html. Accessed December 9th, 2016.
Definition / General
  • LDH measures the amount of serum lactate dehydrogenase (LDH), which is released into the circulation after tissue damage
  • Causes of tissue damage include acute myocardial infarction (AMI), hepatitis and acute renal failure
  • LDH is elevated on the second day after AMI, and remains elevated for up to 4 days
  • LD1 is usually measured
Pathophysiology
  • LDH is an enzyme (EC 1.1.1.27) ubiquitous in tissue (Wikipedia - Lactate dehydrogenase)
  • It has five isoenzymes, each with a different composition of M-type and H-type subunits in a tetrameric structure
  • The M-type isoenzyme is predominant in liver and skeletal muscle
  • The H-type isoenzyme is predominant in heart and renal cortex
  • LDH catalyzes the conversion of pyruvate to lactate in the glycolytic pathway
Diagrams / Tables
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Pyruvate to Lactate conversion

Laboratory
Methodology
  • The measurement of the enzyme uses the reduction of the coenzyme NAD to NADH with increasing optical density and oxidation of lactic acid to pyruvate
  • Alternatively, one can follow the reverse reaction of pyruvate to lactate and NADH to NAD at 340 nm

Indications
  • Patients presenting 12+ hours after the onset of chest pain
    • High levels are suggestive of acute myocardial infarction
  • Staging (S classification) patients with nonseminomatous testicular cancer
  • Evaluating patients with metastatic cancer
  • Assessing nature of pleural / pericardial fluids: ratio of fluid LDH to upper limit of normal serum LDH of more than 0.6 suggests an inflammatory process (exudate)

Limitations
  • Elevated in hemolyzed specimens, since enzyme is present in erythrocytes

Reference ranges
  • A typical range is 105 - 333 IU/L
  • Must interpret values in context of patient clinical findings