“Bad,” or LDL, cholesterol is a major risk factor for heart disease and most people are screened for it as part of their yearly physicals. There’s another marker in the blood that may be a better predictor of heart disease risk , a recent large review suggests. But it’s not part of routine blood testing. Apolipoprotein B (apoB) is a protein that attaches to harmful fat particles in the blood. The apoB protein is found on the surface of harmful lipoproteins like low density lipoprotein, or LDL,