LD ISOENZYMES

Code
900.2450
Name
LD ISOENZYMES
Category
None
Department
Send-Out
Start Date
Expiration Date
Synonyms
LD Iso; LDH Isoenzymes; Lactic Dehydrogenase Isoenzymes
CPT Codes
83625
Site
SBMF
Reference Test
23067
ATLAS Test Code

Specimen Information

Type

Gold, SST

Volume

1.0 ml

Transport Info

Centrifuge and immediately transfer serum to separate plastic tube
Room temperature

Fasting Required?
False
Patient Instructions

Reference Range

See Report

Methodology

Agarose Gel Electrophoresis

Clinical Significance

Diagnosis of myocardial infarction (MI).

Each LD isoenzyme is a tetramer made up of four subunits (polypeptide chains). There are two types of these subunits designated M (muscle) and H (heart). The five LD isoenzymes consist of the five possible combinations of M and H subunits that confer distinct electrophoretic and other properties on each LD isoenzyme. The isoenzymes are designated by their electrophoretic mobility whereby LD1 has been given to the isoenzyme with greatest anodic mobility. The following summarizes the nomenclature, composition and the primary tissue source of LD isoenzymes.• LD1 (H4) - heart (myocardium); • LD2 (H3M) - heart (myocardium); • LD3 (H2M2) - variable amounts in many tissues; • LD4 (HM3) - variable amounts in many tissues; • LD5 (M4) - skeletal muscle, liver.Diagnosis of myocardial infarction (MI) represents the major value of LD isoenzyme electrophoresis. In normal serum, LD2 is the most prevalent isoenzyme and the LD1/LD2 ratio is generally less than 1. The concentrations of LD1 and, to a lesser degree of LD2, increase after MI and the LD1/LD2 ratio becomes greater than 1 (the so called LD1/LD2 flip). The total LD concentration increases by a factor of two to three within 12 to 24 hours after MI. The LD activity reaches its maximum after two or three days and remains at a high level during about two weeks after infarction.The LD isoenzyme analysis is generally run in tandem with CK (creatine kinase) isoenzymes and/or other early cardiac markers to confirm or rule out the diagnosis of MI, assess its severity and monitor the patient’s condition. Because of the rather unique distribution of LD isoenzymes in various tissues, their assay in serum aids in diagnosing tissue damage such as in pulmonary and renal infarctions and hepatic disease.

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