Diagnosis:
Cardiac biomarkers
• LDH has a molecular mass of about 135,000 Da and is a tetramer composed of heart (H) and muscle (M) subunits, which give rise to five isoenzymes. The LDH-1 (H4) isoenzyme is found mainly in heart, brain, and erythrocytes; the LDH-2 (H3M) is found in myocardium; and the LDH-5 isoenzyme predominates in the liver and skeletal muscle.
• In normal serum, LDH-2 is the most common isoenzyme, and the LDH-1/LDH-2 ratio is usually less than 1. The LDH-1 fraction will be greater than the LDH-2 fraction (i.e., “a flipped LDH-1/LDH-2 pattern”) if (1) hemolysis is present or (2) it has been several days since an acute myocardial infarction.
• Haptoglobin is an acute-phase protein. Haptoglobin levels are decreased when there is hemolysis because the released hemoglobin binds haptoglobin and is rapidly cleared from the circulation.
• During hemolysis, significant amounts of LDH-1 isoenzyme are released from the erythrocytes, resulting in a flipped LDH-1/LDH-2 pattern.
• A flipped LDH-1/LDH-2 pattern is not a specific marker for myocardial necrosis.
