What's the Best Cardiac Marker?
The acute coronary syndromes (ACS) are a continuum of ischemic heart disease that spans the entire range from unstable angina, associated with reversible injury; to frank myocardial infarction with large areas of cardiac necrosis. Here are some facts:
- The acute coronary syndromes are the biggest killer in the western world, accounting for approximately 500,000 deaths annually in the U.S. alone.
- Until recently, the magnitude and impact of this disease on women was largely under appreciated. However, the acute coronary syndromes by far account for greater mortality among women than any other cause.
- The economic impact of acute coronary syndromes is estimated at between 3 and 10 billion dollars annually. CHF costs another 30 billion dollars.
- Because of high risk of death and morbidity, ACS must be identified among the estimated 7 million patients with non-traumatic chest symptoms presenting for emergency evaluation each year in the United States. Better testing will also identify many more women at risk when interventions can be instituted.
There has been a lot of discussion recently about the "best" cardiac marker and which of the many newer tests will prove to be the gold standard. Recent guidelines from the National Academy for Clinical Biochemistry suggest Troponin is the most sensitive and specific.
CKMB falls faster than troponin, so is useful in identifying a re-infarction, for example. Myoglobin is an early but very nonspecific marker and should be used only in conjunction with a more specific marker. It is pretty much agreed that total CK and LDH do not provide much useful information.
Because of the financial and human cost of ACS (including MI) it is important whener possible to measure cardiac risk before a heart attack occurs. Probably the most commonly used pre-test is highly specific CRP ( hs-CRP).
Microalbumin, homocysteine and BNP are also used by some ED docs and cardiolgists. Promising new tests of cardiac risk include Ischemic modified albumin (IMA) and Cystacin C among others. What's the current thinking in your lab?