MYOGLOBIN - AN EARLY BIOCHEMICAL MARKER FOR THE DIAGNOSIS OF ACUTE MYOCARDIAL-INFARCTION

Myoglobin is a 17,800 dalton heme protein present in skeletal and cardiac muscle. It is rapidly released into the bloodstream following muscle injury in a temporal pattern. In patients with acute myocardial infarction (AMI), the serum myoglobin level becomes abnormal in about 2 hours, peaks in about 6-9 hours, and becomes normal in 24 to 36 hours after the infarction. Myoglobin measurement between 2 and 12 hours after the myocardial infarction has high clinical sensitivity and specificity. However, false-positive results of myoglobin could be encountered because of skeletal muscle damage and renal failure, while false-negative results could be seen in patients admitted less than 2 hours or more than 24 hours after infarction. False-positive results due to skeletal muscle injury may be eliminated by determining myoglobin to carbonic anhydrase m ratio. Myoglobin can be a good adjunct to electrocardiography in improving the efficiency of early diagnosis of myocardial infarction. Measurement of myoglobin on sequential samples collected on admission and 4 hours later appears to improve the diagnostic performance of myoglobin. Monitoring of the myoglobin levels can also help in evaluating the success of thrombolytic therapy. Use of myoglobin as an early biochemical marker for the diagnosis of AMI, its limitations, and the methods for quantitation are discussed.