High levels of LDL cholesterol and lipoprotein a in the bloodstream, along with conditions like diabetes and hypothyroidism, can lead to the development of atherosclerosis over time. Atherosclerosis occurs when fat, cholesterol, and other substances build up in the arteries in the form of plaque. This plaque hardens and narrows the arteries, reducing blood flow. If a plaque breaks off a coronary artery, it can cause a heart attack. Blood tests can detect high LDL and lipoprotein a levels, and low HDL, as markers for risk of atherosclerosis and coronary heart disease. Lifestyle changes like exercise, diet, weight control and limiting alcohol/saturated fats can help lower cholesterol and reduce risk.