The LDL patterns A and B refer to the size of LDL cholesterol particles in the blood. Some doctors believe that small LDL cholesterol particles in the blood may pose a greater risk for developing atherosclerosis and heart attacks than the absolute level of LDL cholesterol in the blood. The size of LDL cholesterol particles is primarily inherited.
A special blood test called polyacrylamide gradient gel electrophoresis can measure particle size and determine whether a person has blood cholesterol LDL pattern A or LDL pattern B.
Persons with LDL cholesterol pattern A have large, buoyant LDL cholesterol particles. Individuals with pattern A are more likely to have normal blood levels of LDL cholesterol, HDL cholesterol, and triglycerides. Pattern A is usually not associated with an increased likelihood of atherosclerosis.
Persons with LDL cholesterol pattern B have predominantly small and dense LDL cholesterol particles. Pattern B is frequently associated with low HDL cholesterol levels, elevated triglyceride levels, and the tendency to develop high blood sugar levels and type II diabetes mellitus. Individuals with pattern B are also more likely to develop high blood triglyceride levels after a fatty meal (postprandial hyperlipidemia). Pattern B is associated with accelerated atherosclerosis and a 3 to 5- fold increase in heart attack risk. Pattern B is believed to be the most important cause of atherosclerosis in people with normal or near normal total and LDL cholesterol levels.
Some scientists believe that the smaller LDL particles are more dangerous than the larger ones because they can more easily squeeze through the tiny gaps between the cells in the endothelium to reach inside the artery walls. The endothelium is a thin layer of cells which covers the inner wall of the arteries. The cells making up the endothelium have tiny gaps between them. Others postulate that the smaller LDL cholesterol particles are more easily oxidized. Oxidation of cholesterol is significant in the formation of cholesterol plaques.
How can LDL cholesterol size be enlarged?
Even though LDL cholesterol particle size is mainly genetically inherited, individuals who have small LDL particles (pattern B) can increase their particle size through diet, exercise, and medications.
Diets that are low in saturated fat and cholesterol, regular aerobic exercise, and loss of excess body fat have been determined to decrease the number of small LDL particles and increase the number of large LDL particles in the blood. In other words, lifestyle modifications can change pattern B to pattern A.
When lifestyle changes alone are unsuccessful, medications can be used. Even though the statin medications (discussed below) are effective in lowering the absolute levels of LDL cholesterol, they appear to have a limited effect on LDL cholesterol size pattern. Medications such as Nicotinic Acid (niacin) and gemfibrozil (Lopid) have been found effective in many instances in increasing the size of LDL cholesterol particles.
Why is HDL the good cholesterol?
HDL is the good cholesterol because it protects the arteries from the atherosclerosis process. HDL cholesterol extracts cholesterol particles from the artery walls and transports them to the liver to be disposed through the bile. It also interferes with the accumulation of cholesterol in the artery walls by the LDL cholesterol particles.
The risk of atherosclerosis and heart attacks in both men and women is strongly related to HDL cholesterol levels. Low levels of HDL cholesterol are linked to a higher risk, whereas high HDL cholesterol levels are associated with a lower risk.
Very low and very high HDL cholesterol levels can run in families. Families with low HDL cholesterol levels have a higher incidence of heart attacks than the general population, while families with high HDL cholesterol levels tend to live longer with a lower frequency of heart attacks.
Like LDL cholesterol, life style factors and other conditions influence HDL cholesterol levels. HDL cholesterol levels are lower in persons who smoke cigarettes, eat a lot of sweets, are overweight and inactive, and in patients with type II diabetes mellitus.
HDL cholesterol is higher in people who are lean, exercise regularly, and do not smoke cigarettes. Estrogen increases a person’s HDL cholesterol, which explains why women generally have higher HDL levels than men do.
For individuals with low HDL cholesterol levels, a high total or LDL cholesterol blood level further increases the incidence of atherosclerosis and heart attacks. Therefore, the combination of high levels of total and LDL cholesterol with low levels of HDL cholesterol is undesirable whereas the combination of low levels of total and LDL cholesterol and high levels of HDL cholesterol is favorable.
What are LDL/HDL and total/HDL ratios?
The total cholesterol to HDL cholesterol ratio (total/HDL) is a number that is helpful in predicting atherosclerosis. The number is obtained by dividing total cholesterol by HDL cholesterol. (High ratios indicate higher risks of heart attacks, low ratios indicate lower risk).
High total cholesterol and low HDL cholesterol increases the ratio, and is undesirable. Conversely, high HDL cholesterol and low total cholesterol lowers the ratio, and is desirable. An average ratio would be about 4.5. Ideally we want to be better than average if we can. Thus the best ratio would be 2 or 3 or less than 4.
Another ratio is LDL/HDL. The LDL/HDL ratio is actually a more pure ratio than total cholesterol/HDL. Because LDL is a measure of bad cholesterol and HDL is a measure of good cholesterol, whereas the total cholesterol is the sum of HDL, LDL, and the VLDL. Yes, adding up the HDL, LDL and VLDL makes up the total cholesterol measurement.
Revision date: July 3, 2011
Last revised: by Jorge P. Ribeiro, MD