Apo B -- A Better Marker for Heart Attack Risk Than LDL Cholesterol?

A high level of low-density lipoprotein (LDL, or “bad”) cholesterol is an important risk factor for a heart attack. Yet about half of the people who develop coronary heart disease have normal or even low LDL cholesterol levels. Some research suggests that a component of LDL—called apolipoprotein B, or apo B—may be more accurate at predicting coronary heart disease.

A Limitation with LDL Cholesterol Testing
The problem with using LDL cholesterol levels to determine heart attack risk is that the test measures only the amount of cholesterol in the LDL cholesterol particles, not the number or size of these particles. Apo B measurements, on the other hand, provide information on the number of LDL cholesterol particles.

Apo B is a protein found on the surface of LDL cholesterol particles. Because each LDL particle contains only one molecule of apo B, the total amount of apo B in the blood is equivalent to the number of LDL cholesterol particles. The size of these particles can sometimes be inferred from the total amount of apo B and the LDL cholesterol level.

For example, people with a higher apo B value than LDL cholesterol value tend to have smaller, denser LDL cholesterol particles. Studies have shown that small, dense LDL cholesterol particles are more strongly associated with heart attack risk than large, “fluffy” LDL cholesterol particles.

Preliminary But Compelling Evidence on Apo B
Research published in The Lancet reviewed five studies of LDL cholesterol and apo B in nearly 200,000 people. The researchers concluded that high levels of apo B were more strongly linked with future heart attack risk than LDL cholesterol levels.

A second report published in Circulation studied more than 1,500 adults. The participants were categorized based on their LDL cholesterol and apo B levels. Those with normal LDL cholesterol and high apo B levels were more likely to have other heart attack risk factors—such as low high-density lipoprotein (HDL) cholesterol and high triglyceride levels, abdominal obesity, and high fasting insulin levels—than those with high LDL cholesterol and normal apo B levels. The researchers pointed out that if apo B levels were used to determine who needs cholesterol-lowering medication, 25% of the participants with normal LDL cholesterol levels would meet the criteria.

The Bottom Line on Apo B
Apo B is measured with a simple blood test. Proponents of apo B argue that the test is accurate, inexpensive, and does not require fasting, as LDL cholesterol testing usually does. However, the American Heart Association has determined that the evidence to date is not strong enough to recommend that apo B testing become standard procedure.

Even apo B researchers recognize that LDL cholesterol is an important predictor of heart attack risk and suggest that apo B is most helpful for predicting risk in people with normal or low LDL levels but high triglyceride levels. Overall, if one’s LDL cholesterol value is high, an apo B measurement is not necessary.

Another important consideration is that LDL cholesterol levels can be used to guide therapeutic interventions to decrease heart attack and stroke risk, but no data have shown that apo B levels can be used in the same way.