Lipoprotein(a)

High levels of lipoprotein(a), abbreviated as Lp(a), are a risk factor for heart attack or stroke. Lp(a) levels greater than 30 mg/dL are considered high. The structure of Lp(a) is similar to LDL, except that Lp(a) contains a protein called apo(a), which resembles a blood protein called plasminogen. When converted into the enzyme plasmin, plasminogen helps eliminate blockages in the arteries by breaking down fibrin (a major component of blood clots).

Two explanations have been proposed for why Lp(a) raises the risk of heart attacks. First, Lp(a) may interfere with the conversion of plasminogen to plasmin, thus increasing the risk of blood clots by reducing the beneficial action of plasmin. Second, like LDL, Lp(a) can be deposited in the walls of arteries and contribute to plaque formation.

Lp(a) levels are difficult to lower. High doses of niacin (a B vitamin) and estrogen supplementation can lower Lp(a) levels slightly, but neither is recommended for this purpose. Also, testing ofLp(a) levels in the general population is not recommended.

Apolipoprotein B

High levels of apolipoprotein B (apoB) indicate a greater risk of a heart attack. ApoB is a protein found on the surface of LDL particles. People with higher levels of apoB than LDL cholesterol tend to have smaller, denser LDL particles. Your doctor may want to test your apoB levels if you have normal or low LDL levels but borderline high or elevated triglyceride levels. Research shows that in this situation, apoB is a better predictor than LDL cholesterol for predicting the risk of a heart attack.

Publication Review By: Roger S. Blumenthal, M.D. and Simeon Margolis, M.D., Ph.D.

Published: 11 Mar 2011

Last Modified: 15 Jan 2015