Cardiac marker tests identify blood chemicals associated with myocardial infarction (MI), commonly known as a heart attack. The myocardium is the middle layer of the heart wall composed of heart muscle. Infarction is tissue death caused by an interruption in the blood supply to an area.
Cardiac markers help physicians to assess acute coronary syndromes and to identify and manage high-risk patients. Creatine kinase-MB (CK-MB), myoglobin, homocysteine, C-reactive protein (CRP), troponin T (cTnT), and troponin I (cTnI) are all used for assessment of the suspected acute myocardial infarction. CK-MB, cTnT, and cTnI may also be used to identify and manage high-risk patients.
C-reactive protein results may be affected by the use of oral contraceptives, NSAIDs, steroids, salicylates, and intrauterine devices (IUDs). Homocysteine levels may be affected by smoking, diabetes, and coffee.
These articles contained the following recommendations regarding cardiac marker laboratory testing.
- Troponin T or I is the preferred cardiac marker.
- CK-MB is an acceptable alternative, if troponin is not available.
- Total creatine kinase (CK) is no longer useful & should be discontinued.
- Troponin should be measured within 6 hours of the onset of symptoms.
- If the first troponin result is negative, a second sample should be obtained between 6 & 12 hours of symptom onset.
- Cardiac Marker results should be available within 30 to 60 minutes.
- An abnormal troponin result should be defined as >99th percentile of a normal population
- Troponin assay must have a low level of imprecision at the cutoff point (CV<10%).
Based on these recommendations, a group of physicians from Cardiology, Emergency Medicine and Pathology at our hospital decided to implement the following changes in cardiac marker testing.
- Create a new Cardiac Marker Panel for the Emergency Department that includes CK-MB & Troponin at 0, 3 & 6 hours after admission.
- Retain the current Acute Cardiac Injury Panel that includes CK-MB & Troponin at 0, 6 & 12 hours for admitted patients.
- Eliminate total CK from all cardiac panels.