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Stroke Blood Tests - PLAC Test

PLAC (Lp-PLA2) Test

The PLAC test measures your blood levels of the enzyme Lp-PLA2, which is related to LDL (bad) cholesterol. Like C-reactive protein, Lp-PLA2 is associated with inflammation and atherosclerosis; high levels of the enzyme are thought to promote the development of vulnerable plaque, buildup on the artery wall that is likely to rupture or break apart, causing a stroke or heart attack.

Many studies have found that Lp-PLA2 predicts your risk of developing heart disease in the future, independent of other heart disease risk factors.1 In the past few years, evidence has been growing that Lp-PLA2 can also help predict your risk of having a first blocked-vessel stroke2 or your risk of having another stroke if you have already had one.3

The largest study so far of blocked-vessel stroke in older women (929 postmenopausal female stroke patients and 935 controls) found that women with high levels of Lp-PLA2 had a 55% higher risk of stroke than women with low levels, even after other risk factors were taken into account. This increased risk was only seen in the 61% of women who were not taking hormone therapy. However, this does not mean you should take hormone therapy to reduce the impact of LP-PLA2; overall, hormone therapy increases your stroke risk. Stroke risk was highest in women who had high levels of both C-reactive protein and Lp-PLA2; these women were twice as likely to have a stroke compared to women with low levels of both markers.4

Not all studies have found that Lp-PLA2 can predict stroke more accurately than just looking at standard risk factors, however. In more than 28,000 healthy middle-aged women in the Women’s Health Study, elevated Lp-PLA2 levels did not predict future heart attack or stroke after other risk factors were taken into account.5

The PLAC test is approved by the FDA to help assess a person’s risk for coronary artery disease and blocked-vessel stroke. The test may be useful in patients who are at intermediate risk for stroke, in whom it is not clear if medication or other treatment is necessary. For example, in a woman who has low cholesterol and a single major stroke risk factor (such as a family history of stroke), the PLAC test could help doctors better understand her true stroke risk.

For now, the PLAC test is not routinely used to determine your risk of having a stroke. People with higher levels of Lp-PLA2 are at increased risk for stroke, but the cutoff level (above which you can be considered high risk) is not known. In addition, specific treatment to lower Lp-PLA2 levels does not yet exist. Clinical trials are underway on a drug called darapladib to find out if blocking Lp-PLA2 can prevent heart disease and stroke.

References

  1. Daniels LB, Laughlin GA, Sarno MJ, Bettencourt R, Wolfert RL, Barrett-Connor E. Lipoprotein-associated phospholipase A2 is an independent predictor of incident coronary heart disease in an apparently healthy older population: the Rancho Bernardo Study. J Am Coll Cardiol. Mar 4 2008;51(9):913-919.
  2. Oei H-HS, van der Meer IM, Hofman A, et al. Lipoprotein-Associated Phospholipase A2 Activity Is Associated With Risk of Coronary Heart Disease and Ischemic Stroke: The Rotterdam Study. Circulation. February 8, 2005 2005;111(5):570-575.
  3. Elkind MS, Tai W, Coates K, Paik MC, Sacco RL. High-sensitivity C-reactive protein, lipoprotein-associated phospholipase A2, and outcome after ischemic stroke. Arch Intern Med. Oct 23 2006;166(19):2073-2080.
  4. Wassertheil-Smoller S, Kooperberg C, McGinn AP, et al. Lipoprotein-Associated Phospholipase A2, Hormone Use, and the Risk of Ischemic Stroke in Postmenopausal Women. Hypertension. February 7 2008.
  5. Blake GJ, Dada N, Fox JC, Manson JE, Ridker PM. A prospective evaluation of lipoprotein-associated phospholipase A(2) levels and the risk of future cardiovascular events in women. J Am Coll Cardiol. Nov 1 2001;38(5):1302-1306.

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