PLAC blood test for sudden cardiac arrest and stroke risk
Life Extension Foundation (LEF) unveiled a new blood test in an article in this month’s Life Extension Magazine (November 2008). Unlike cholesterol testing, which simply gives a measurement of high-density (HDL) and low-density (LDL) lipoprotein levels and provides little information about acute risk of stroke or heart attack, the PLAC® blood test “can accurately identify artherosclerotic plaque that is vulnerable to rupture,” essentially providing a direct assessment of sudden heart attack and stroke risk.
The PLAC® test, developed by diaDexus, Inc., provides this assessment by measuring levels of lipoprotein phospholipase A2 (Lp-PLA2), an enzyme that is directly involved in endothelial dysfunction leading to atherosclerosis (an inflammatory response of the blood vessel wall), plaque accumulation (build-up of lipid deposits inside blood vessels), and rupture (breaking loose of plaque which can then block a blood vessel, causing heart attack or stroke). The PLAC® test specifically measures Lp-PLA2 associated with oxidized LDL particles. In research studies, high levels of Lp-PLA2 have been determined to be highly specific for plaque inflammation: an elevated PLAC® test indicates an increased amount of inflamed atherosclerotic plaques and thus a higher risk of plaque rupture.
Because of the sensitivity and high specificity of the PLAC® test for such inflammation, the predictive value of the test for risk of cardiac arrest and/or stroke is higher than other markers for the prediction of acute events. Furthermore, the PLAC® test is inexpensive and convenient in comparison to CT and other imaging procedures since it involves only the collection of a blood sample.
In general, the PLAC® test is appropriate for those known to be at high risk for cardiovascular disease and stroke, and LEF recommends that it should be performed once a year in persons who are obese or are regular smokers, those with high blood pressure or cholesterol, type 2 diabetes, or a family history of stroke and coronary heart disease. The PLAC® test can be used to guide patient treatment options: from their article, the LEF panel “recommends that patients with high Lp-PLA2 levels be upgraded from moderate risk to high risk, or from high risk to very high risk. In these patients, a suitable goal is to lower LDL to 100 mg/dL in high-risk patients and to 70 mg/dL in very high-risk patients.”
The PLAC® test is currently the only blood test approved by the FDA to assess atherosclerotic risk for coronary heart disease and stroke. While this is useful for guiding patients in their use of known treatment options, it is not known whether lowering Lp-PLA2 itself will result in a reduction of this risk. A large study (IBIS-2 trial) is now underway to shed more light on this topic. In the meantime, LEF claims that the PLAC® test is by far the most reliable, convenient, and inexpensive method for determining one’s risk of acute ischemic cardiovascular events and is undoubtedly a beneficial tool for helping patients to keep tabs on their risk level and to implement a more aggressive treatment strategy if indicated.