For assessing heart disease risk, a standard cholesterol test doesn't always tell the whole story. Who should consider an additional test?
A standard cholesterol test (also known as a lipid profile or lipid panel) tells you the amount of cholesterol and triglyceride carried in your blood. These lipids (fats) travel inside tiny particles called lipoproteins. Created in your intestines and liver, lipoproteins come in a range of shapes, sizes and densities.
The value of greatest concern is low-density lipoprotein (LDL) cholesterol, often referred to as "bad" cholesterol. Too much LDL in the bloodstream helps to create the plaque that accumulates inside arteries, raising the risk of a heart attack. The higher your LDL, the higher your risk of having a heart attack.
However, about half of heart attacks occur in people who have a "normal" LDL cholesterol value (also referred to as an optimal or near-optimal LDL; see "The range of LDL cholesterol"). What might explain this observation? In addition to LDL, other lipoproteins can contribute to clogged arteries. Known as atherogenic particles, they include intermediate-density lipoprotein (IDL), very-low-density lipoprotein (VLDL), and chylomicrons, the largest, lowest-density particles, which consist mainly of lipid.
For those with known heart disease, doctors recommend an LDL of less than 70 mg/dL.
Less than 100 mg/dL is optimal; 100-129 mg/dL is near optimal/above optimal; 130-159 mg/dL, borderline high; 160-189 mg/dL, high; 190 mg/dL and above, very high.
Particle numbers, explained
Some cholesterol tests report your "non-HDL cholesterol," which is your total cholesterol minus the high-density lipoprotein (HDL). While that value captures all the cholesterol in the atherogenic particles, it doesn't tell you one potentially important thing: the actual number of particles.
"There's increasing recognition that it's not just the cholesterol that matters, but the number of lipoprotein particles," says Dr. Samia Mora, a cardiologist at Harvard-affiliated Brigham and Women's Hospital.
That's because both size as well as composition matter: larger LDL particles carry more cholesterol, while smaller particles carry less. If the LDL particles in your blood are mostly on the small side, you will have a greater number of these particles for any given LDL cholesterol level compared to someone with larger particles. The more particles there are traveling through your blood, the more likely they are to become stuck inside artery walls.
Growing evidence suggests that knowing the total number of all atherogenic lipoprotein particles is a better indicator of cardiovascular disease risk than the standard LDL cholesterol value. This number can be assessed with an inexpensive, widely available test that measures apolipoprotein B (apoB), a single protein found on all atherogenic particles.
So why isn't apoB testing done routinely? In most cases, an LDL value is sufficient. In general, if it's high, there's no reason to check your apoB because you already know you're at higher risk for heart disease. (You can assess your risk and possible need for a cholesterol-lowering statin here: www.health.harvard.edu/heartrisk.)
However, the thinking about apoB's relevance is evolving. In fact, the current guidelines from the European Society of Cardiology recommend apoB testing to better assess a person's heart attack risk. The guidlines of the American College of Cardiology/American Heart Association say that apoB is better than LDL cholesterol for assessing risk and that people with apoB levels higher than 130 milligrams per deciliter (mg/dL) might benefit from taking a statin to lower their heart attack risk. They suggest apoB testing for people with triglyceride values of 200 mg/dL or higher.
Some cardiologists, including Dr. Mora, advocate more widespread apoB testing. Consider a group of healthy people, all with LDL cholesterol values of around 120 mg/dL. For those who eat a healthy diet and are in a normal weight range, there's no reason for an apoB test. But those who have signs of an unhealthy metabolism, such as prediabetes, a big belly, or elevated triglycerides, are far more likely to have a high apoB, Dr. Mora explains. At least a quarter of the population may fall into this second category and should consider getting an apoB test, she says. She also recommends apoB testing in people with a family history of heart disease.
The good news is that even if your apoB is high, lifestyle habits such as following a Mediterranean-style eating pattern and getting regular exercise can help bring it down.