Page 110 - Clinical Biochemistry

CK-MB values return to normal 2~3 days after the event.

3- Lactate dehydrogenase (LDH)

• Lactate dehydrogenase (LDH):
• LDH is a hydrogen transfer enzyme that catalysis the oxidation of L-Lactate to Pyruvate
• LDH has 5 isoenzymes, each having different electrophoretic mobility, physical and

chemical prop.
• LDH1 and LDH2 are present in RBCs and heart. LDH1 is a greater rise during acute

myocardial infarction (AMI).
• LDH5 present in liver, skeletal muscle.
• Both total and LDH isoenzymes are elevated in myocardial injury.
• Usually the amount of LDH-2 in the blood is higher than amount of LDH1. Patient with

AMI have more LDH-1 than LDH-2 (ratio>1) this is called "Flipped Ratio".
• An elevated level of LDH=1 with flipped ratio has a sensitivity and specificity of

approximately 75%-90% for detection of AMI.
• In AMI, Level of LDH-1 are elevated 12–18 hr after AMI, peak at 48-72 hr and return to

normal in 7-10 days.

Protein Markers

1- Myoglobin (mb)
• O2 binding protein of cardiac and skeletal muscle.
• Low molecular weight and cytoplasmic location, early appearance in circulation after

muscle injury
• Cleared rapidly by kidney → unreliable as a long-term marker of cardiac damage
• Cardiac muscle trauma, skeletal muscle trauma, crush injury and AMI cause an increase in

myoglobin levels.
• Very sensitive early diagnostic marker for AMI (%90-100), poor clinical specificity (%60-

95).
• Rises as early as 1 hr. after AMI, peaks in 4-12 hr. → reflects the early course of myocardial

necrosis, lasts for 24 hr.
• The role of myoglobin in the detection of AMI is within 0-4hr.
2- Cardiac troponins
• Tropnin is heteromeric protein playing an important role in regulation of skeletal and

cardiac muscle contraction.