CARDIAC TROPONIN-I - A HIGHLY SPECIFIC BIOCHEMICAL MARKER FOR MYOCARDIAL-INFARCTION

Creatine kinase MB isoenzyme (CK-MB) has become the biochemical marker of choice for diagnosing myocardial infarction (MI). However, limitat ions of CK-MB measurement such as delayed response and short duration of elevation following an MI as well as lack of specificity necessitat e the finding of a more suitable diagnostic marker. Cardiac troponin I (cTnI), a heart tissue-specific regulatory protein, has received much attention recently as a potential choice to replace CK-MB. Monoclonal antibody based immunoassays have shown that cTnI is undetectable in s era of healthy blood donors. cTnI concentration is <3.1 ng/mL in sera of 95% of hospitalized patients who have no heart disease. Following a n MI, cTnI becomes elevated approximately 6 hours after the onset of c hest pain and its concentration peaks around 12 hours. In contrast to the short duration of elevation of CK-MB, cTnI remains diagnostic for at least a week after MI. cTnI appears to be extremely cardiac-specifi c. No cTnI has been found in patients who had rhabdomyolysis but no ca rdiac muscle injury even when CK reached >70,000 U/L and CK-MB >270 ng /mL. cTnI was 100% sensitive and 100% specific in detecting MI in pati ents with acute (n = 39) and chronic (n = 10) skeletal muscle injury, chronic renal failure (n = 159), or in marathon runners (n = 10).