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Clinical Chemistry

Cardiac-related tests

Lactate Dehydrogenase (LDH)


Author: Larry Bernstein, M.D., Triplex Consulting (see Reviewers/Authors page)
Revised: 12 December 2010, last major update December 2010
Copyright: (c) 2003-2010, PathologyOutlines.com, Inc.

General
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● 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

Physiology
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● LDH is an enzyme (EC 1.1.1.27) ubiquitous in tissue (Wikipedia)
● 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
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Pyruvate to Lactate conversion


Methodology
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● 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
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● 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
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● Elevated in hemolyzed specimens, since enzyme is present in erythrocytes

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

Additional references
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Science 1970;168:1236, Clin Chem 1988;34:2031, Clin Chem 1983;29:589, Clin Chem 1986;32:624, Clin Chem 1988;34:2167, Clin Chem 1977;23:1928, Clin Chem 1986;32:792

End of Clinical Chemistry > Cardiac-related tests > Lactate Dehydrogenase (LDH)


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