Biochemical markers in acute coronary syndrome

Biochemical markers in acute coronary syndrome

Biochemical markers in acute coronary syndrome:

1. Troponin: high sensitivity, high specificity for myocardial tissue
2. CK-MB: less tissue specific, but better specificity for irreversible injury
3. Myoglobin: for rapid diagnosis

Troponins for evaluation and management of acute coronary syndrome

Advantages of troponin are that they are useful in risk stratification, have a better sensitivity and specificity than CK MB, can detect recent myocardial infarction and facilitates the selection of treatment modality.

Disadvantages of troponin are that the sensitivity is low in the early hours (< 6h), needs repeat measurements at 8 – 12 hours if negative, and has limited ability to detect late minor reinfarction.

Recommendations for the use of troponins in acute coronary syndrome

Troponins are useful as a single test to efficiently diagnose non ST elevation myocardial infarction. One should be familiar with the diagnostic cutoffs in the local lab. Delta troponin is the serial elevation of troponin over 1 or 2 hours. This needs two serial samples and delta troponin ranges for the lab technique should be available. Delta troponin is useful in the early rule in early rule out strategy in the emergency department.

Non myocardial infarction causes of troponin elevation

Cardiac failure with myonecrosis, cardiac surgery, myocarditis and renal failure are the important causes of troponin elevation other than myocardial infarction. Now these are classified under myocardial injury and have similar prognostic significance as troponin elevations due to myocardial infarction.

Creatine kinase (CK-MB)

Advantages of creatine kinase are that the assay is rapid, cost- efficient, accurate and detects early reinfarction.

Disadvantages of creatine kinase are the lower specificity and low sensitivity during very early MI (6 hours after onset) or later after onset of symptoms (>36hr) and for minor myocardial damage.

CK-MB isoforms

Advantage of CK-MB isoforms is for the detection of early MI (3-6 hrs after onset of symptoms).

Disadvantages of CK-MB isoforms are that the specificity profile is similar to that of CK-MB and current assays require special expertise (used predominantly in research centers).

Myoglobin

Advantages of myoglobin are the high sensitivity and utility in early detection of MI (2hrs after onset of symptoms) and hence most useful in ruling OUT an MI.

Disadvantages of myoglobin are the very low specificity in setting of skeletal muscle injury or disease, rapid return to normal and it should not be used in isolation.

Other markers

CRP

Patients without biochemical evidence of myocardial necrosis but who have an elevated CRP are at an increased risk of an adverse outcome.

Others
Elevated levels of interleukin-6 and serum amyloid A have similar predictive value as CRP.