An ApoB (Apolipoprotein B) test is a blood test measuring ApoB protein, a key component of “bad” cholesterol (LDL, VLDL) that indicates your risk for plaque buildup, atherosclerosis, heart attack, and stroke, especially when standard lipid panels are normal but family heart history is present. It helps doctors fine-tune cardiovascular risk, monitor treatments (like statins), and diagnose some genetic lipid disorders, often requiring a 9-12 hour fast for accurate results, with lower levels generally better for heart health