Cardiac marker
From Wikipedia, the free encyclopedia
| Elevation of levels of transaminase and lactic acid dehydrogenase (LDH) Classification and external resources |
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| ICD-10 | R74.0 |
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| ICD-9 | 790.4 |
Medical tests that are often referred to as cardiac markers include:
- cardiac troponin (the most sensitive and specific test for myocardial damage)
- creatine kinase (CK, also known as phosphocreatine kinase or creatine phosphokinase)
- Aspartate transaminase (AST, also called Glutamic Oxaloacetic Transaminase (GOT/SGOT) or aspartate aminotransferase (ASAT))
- lactate dehydrogenase (LDH)
- Myoglobin (Mb) has low specificity for myocardial infarction and is used less than the other markers.
Cardiac markers are substances released from heart muscle when it is damaged as a result of myocardial infarction. Depending on the marker, it can take between 2 to 24 hours for the level to increase in the blood. Additionally, determining the levels of cardiac markers in the laboratory - like many other lab measurements - takes substantial time. Cardiac markers are therefore not useful in diagnosing a myocardial infarction in the acute phase. The clinical presentation and results from an ECG are more appropriate in the acute situation.
[edit] See also
- Myocardial markers in myocardial infarction
Ischemia-Modified Albumin (IMA) can be detected via the albumin cobalt binding (ACB) test, a limited available FDA approved assay. Myocardial ischemia alters the N-terminus of albumin reducing the ability of cobalt to bind to albumin. IMA measures ischemia in the blood vessels and thus returns results in minutes rather than traditional markers of necrosis that take hours. ACB has low specificity therefore generating high number of false positives and must be used in conjunction with typical acute approaches such as ECG and physical exam. Additional studies are required.
Quick summary of Cardiac Enzymes Troponin is released during MI from the cytosolic pool of the myocytes. Its subsequent release is prolonged with degradation of actin and myosin filaments. Because it has increased specificity compared with CK-MB, troponin is a superior marker for myocardial injury. Differential diagnosis of troponin elevation includes acute infarction, severe pulmonary embolism causing acute right heart overload, heart failure, myocarditis. Troponins can also calculate infarct size but the peak must be measured in the 3rd day.
CK-MB resides in the cytosol and facilitates high energy phosphates into and out of mitochondria. It is distributed in a large number of tissues even in the skeletal muscle. It is relatively specific when skeletal muscle damage is not present. Since it has a short duration, it cannot be used for late diagnosis of acute MI but can be used to suggest infarct extension if levels rise again.
Lactate dehydrogenase catalyses the conversion of pyruvate to lactate. LDH-1 isozyme is normally found in the heart muscle and LDH-2 is found predominately in blood serum. A high LDH-1 level to LDH-2 suggest MI. LH is not as specific as troponin. LDH levels are also high in tissue breakdown or hemolysis. It can mean cancer, meningitis, encephalitis, or HIV.
Myoglobin is the primary oxygen-carrying pigment of muscle tissue. It is high when muscle tissue is damaged but it lacks specificity.
Pro-brain natriuretic peptide is increased in patients with heart failure. It has been approved as a marker for acute congestive heart failure. Pt with < 80 have a much higher rate of symptom free survival within a year. Generally, pt with CHF will have > 100.
[edit] Further reading
- Ross G, Bever F, Uddin Z, Devireddy L, Gardin J (2004). "Common scenarios to clarify the interpretation of cardiac markers.". J Am Osteopath Assoc 104 (4): 165-76. PMID 15127984.Full text
[edit] External links
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