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Clinical Chemistry

Cardiac-related tests

Lactate Dehydrogenase isoenzyme 1 (LD1)


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 with an acute myocardial infarction (AMI) due to tissue damage
● LDH is elevated on the second day after chest pain and remains elevated for up to 4 days
● LD1 is the heart specific form of the enzyme present in AMI between 12 and 24 hours after onset of chest pain

Physiology
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● LDH is an enzyme (EC 1.1.1.27) ubiquitous in tissue
● It has five isoenzymes, each with a different composition of M-type and H-type subunits in a tetrameric structure
● LD1 (HHHH) is present in cardiac muscle and erythrocytes

Methodology
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● LD2 is usually the predominant form in serum
● In acute myocardial infarction, the serum levels of LD1 are greater than LD2 (a "flipped pattern")
● However, the use of LD1 to diagnose AMI has been largely superseded by Troponin I or T
● The isoenzyme 1 of LD is measured by immunoprecitation of LD 2-5 and measuring the residual activity; also by electrophoresis and staining of agarose media

Indications
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● Patients presenting 12+ hours after the onset of chest pain or other symptoms suggestive of an acute myocardial infarction

Limitations
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● The LD1 isoenzyme typically is elevated in acute renal failure and with hemolytic anemia

Reference ranges
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● Must interpret values in context of clinical findings

End of Clinical Chemistry > Cardiac-related tests > Lactate Dehydrogenase isoenzyme 1 (LD1)


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