High levels of cholesterol in the blood, Serum Cholesterol
What is cholesterol?
Cholesterol is a fat-like substance (lipid). About 80 percent of cholesterol is manufactured in the liver. The remaining cholesterol is consumed in cholesterol-rich foods such as meat, eggs or dairy products. Cholesterol is vital to good health. The body uses cholesterol to:
Assist in the manufacture of hormones
Break down carbohydrates and proteins
Help form a protective coating around nerves
Build cell walls and produce bile (the word cholesterol is Greek for “bile solids”)
Cholesterol is carried through the bloodstream by lipoproteins. Lipoproteins are proteins that wrap around cholesterol and other fatty materials and transport them through the bloodstream. There are five major kinds of lipoproteins, each of which has a different function in the body. They are:
High-density lipoproteins (HDL)
“Good” cholesterol, HDLs move easily through the blood and are actually beneficial. They are stable and do not stick to artery walls. They help prevent heart disease by carrying cholesterol away from the arteries and back to the liver, where the process of its removal from the body begins. Liver damage, from alcohol abuse or other conditions, can undo the beneficial effects of HDLs.
Low-density lipoproteins (LDL)
“Bad” cholesterol, LDLs contain more fat and less protein than HDLs. LDLs are unstable and tend to fall apart. They are more likely to adhere to the walls of the artery and penetrate the protective inner lining of cells (e.g., the endothelium). Once cholesterol has migrated into the inner wall of the artery, it oxidizes and attracts other fatty substances (e.g., triglycerides), sticky blood-clotting materials (e.g., fibrin and platelets) and white blood cells. Together, these substances form the building materials for plaque deposits, which are the hallmark of atherosclerosis, or "hardened arteries." Atherosclerosis is the leading cause of coronary artery disease, which is the leading cause of heart attack and death in the United States. LDL reduction is a primary therapeutic goal among people with abnormal cholesterol levels (e.g., dyslipidemia). Many people with high levels of "bad" cholesterol also have high triglyceride levels because both types of fats have similar risk factors (e.g., obesity and diabetes).
Very low-density lipoproteins (VLDL)
These are extremely harmful lipoproteins that carry triglycerides and cholesterol.
Like VLDLs, these also carry triglycerides and cholesterol.
These are very large particles that are rich in triglycerides.
Together, LDL, VLDL and the intermediate-density lipoproteins are sometimes referred to as non-HDLs. A high non-HDL is an indicator of increased risk for heart attack and angina.
Finally, advances in research techniques have made it possible to measure the levels of individual lipoproteins in the blood. Lipoprotein “a” – abbreviated Lp(a) – is associated with increased risk of heart disease when values are greater than 30 milligrams per deciliter. Lp(a) can sometimes be detected in patients with premature coronary heart disease, which is defined as heart disease that appears in men who are younger than 55 years old and women who are younger than 65 years old.
A second blood lipid known as apolipoprotein B (apo-B) may be helpful in determining cardiovascular risk. According to some studies, apo-B may even be a better predictor that LDL cholesterol because apo-B has been implicated in the early formation of arterial plaque. Some researchers believe that one of the first steps in the atherosclerotic process is retention of apo-B in the deep arterial wall.
Researchers are also finding that the size and number of cholesterol particles may be associated with human longevity. Studies have shown that people with higher LDL particle number are more likely to suffer from a heart attack than people with lower LDL particle number, independent of overall LDL levels. Also, some research has shown that smaller, more dense LDL particles are more dangerous than larger, looser LDL particles.
Newer cholesterol tests are emerging that can measure for these characteristics. For instance, some researchers believe that the ratio of apolipoprotein A to apolipoprotein B may be a better indicator of heart attack risk than total cholesterol. Still other tests can measure for Lp(a) and LDL particle size and number. Currently, these tests are not part of the standard lipid profile. However, patients wishing to know more information about them should consult their cardiologist.
What is high cholesterol?
Abnormal cholesterol levels are considered a major risk factor for heart attack because cholesterol is intimately related to hardening of the arteries, or atherosclerosis. Using data from the Framingham heart study, physicians are able to use risk factors such as high cholesterol to determine a person's 10-year risk of experiencing a heart attack. This risk level helps guide treatment.
Risk factors include:
Age (45 years or older for men; 55 years or older for women, or premature menopause)
High blood pressure
A diet high in saturated fats
Lack of exercise
A family history of cardiovascular disease
Patients are in this category if they:
Are at high risk (see below)
Have multiple risk factors, or severe and poorly controlled risk factors
Have coronary artery disease, peripheral arterial disease, cerebrovascular disease or other form of atherosclerosis
Two or more known risk factors (see above) that give them a greater than 20 percent risk of heart attack within 10 years
Have two or more risk factors for coronary heart disease, together with a 10 to 20 percent risk of heart attack within 10 years
Have none of the above factors
It is recommended that people at high risk for heart attack aim for a lower LDL cholesterol level than healthy people or people at moderate risk.
Although cholesterol levels are at least partially determined by genetic factors, they are also sensitive to diet and lifestyle. Cholesterol levels can rise to abnormally high levels when someone eats a diet high in saturated fats or trans fats – especially when that person is obese and/or rarely exercises (even moderate exercise has a heart-healthy effect). In particular, trans fats are especially dangerous. Trans fats not only increase levels of “bad” LDL cholesterol, but also decrease “good” HDL levels. This is especially worrisome because trans fats (which prolong the shelf life of processed foods) are common ingredients in potato chips and other snack foods, many types of margarine and shortening, and deep fried and fast foods. As of January 1, 2006, all processed foods in the United States were required to list trans fatty acid levels on their nutritional labels.
High cholesterol levels can also be caused by a number of different genetic conditions. The most widespread inherited cholesterol disorder is familial hypercholesterolemia (FH). The cholesterol levels of people with this disorder may reach as high as 550 milligrams per deciliter – almost four times the level considered desirable for the average person. With cholesterol this high, people with FH are at a high risk for an early heart attack, regardless of the presence of other risk factors. If FH is suspected, children as young as 2 years of age may be appropriate for a cholesterol screening.
Another genetic condition associated with high cholesterol levels is familial dysbetalipoproteinemia (or familial combined hyperlipoproteinemia) in which cholesterol and triglyceride levels are elevated.
Role of cholesterol in heart disease
Cholesterol is intimately related to the development of atherosclerosis, which is a leading cause of heart attack and death in the United States. During the atherosclerotic process, cholesterol is carried into the inner lining of arteries on LDL molecules. Inside the artery, the cholesterol oxidizes, causing an injury to the artery wall and inflammation. Inside the artery, the cholesterol combines with white blood cells and other materials to create a lipid foam. This lipid foam provides the building material for plaque deposits on the inner wall of arteries, including the coronary arteries in the heart and the carotid arteries in the brain.
As plaque deposits grow, they may attract calcium and other minerals that form a hard, brittle shell over the deposit. If the deposit grows large enough, it may obstruct the flow of the blood through the artery, especially during times of stress or increased demand for oxygen such as exercise. In the heart, this can cause a type of chest pain known as angina. In the brain, this can cause a kind of “mini stroke” known as a transient ischemic attack. Both are very serious warning signs that a plaque rupture may be imminent. If the plaque deposit ruptures, a blood clot may rapidly form, causing a heart attack or stroke.
Although the National Center for Health Statistics reported that Americans’ average total cholesterol levels dropped considerably between 1978 and 1990, the American Heart Association reported that 104.7 million American adults still have borderline-high cholesterol levels (200 to 239 milligrams per deciliter). Of these, about 37 million have high cholesterol levels (240 milligrams per deciliter). Taken together, these statistics mean that the average American’s cholesterol level puts him or her at greater risk of heart disease or stroke.
Understanding cholesterol numbers
The guidelines for healthy cholesterol levels are set by the National Heart, Lung and Blood Institute (NHLBI). Recommended cholesterol levels depend on a person’s 10-year risk of a heart attack, according to his or her coronary risk profile. This risk level is determined by the presence of risk factors such as a family history of heart attack, smoking, obesity, lack of exercise and other measures. People at elevated risk should strive for lower cholesterol levels than people who are at low or moderate risk. However, the ultimate therapeutic goal depends on each physician’s judgment.
The recommended cholesterol levels for patients at low to moderate risk of a heart attack are as follows (in milligrams per deciliter [mg/dL]):
Total Cholesterol (Low-moderate risk)
Total Cholesterol Level
Less than 200 mg/dL
200 to 239 mg/dL
240 mg/dL and higher
LDL Cholesterol (Low-moderate risk)
LDL Cholesterol Level
Less than 100 mg/dL
100 to 129 mg/dL
Near optimal/above optimal
130 to 159 mg/dL
160 to 189 mg/dL
190 mg/dL and higher
HDL Cholesterol (Low-moderate risk)
HDL Cholesterol Level
Less than 40 mg/dL for men and less than 50 mg/dL for women
Low (increased risk)
60 mg/dL and higher
Triglycerides (Moderate risk)
Less than 150 mg/dL
150 to 199 mg/dL
200 to 499 mg/dL
500 mg/dL and higher
Labs outside of the United States may use different units of measure for cholesterol levels. To convert a cholesterol level from milligrams per deciliter (mg/dL) to international units (IU), multiply the mg/dL cholesterol level by 0.0259 millimoles per liter (mmol/L). For example, a cholesterol level of 200 mg/dL is equal to a cholesterol level of 5.18 IU.
Hypercholesterolemia, or high cholesterol, is diagnosed by measuring total cholesterol levels, as well as by separate HDL and LDL levels. The total cholesterol equals HDLs + LDLs + 1/5 triglycerides.
Directly measuring LDL cholesterol is difficult and expensive. However, LDL can be reliably calculated by directly subtracting HDL and triglycerides (which are easier to measure) from the total cholesterol, as long as triglycerides are under 400. However, this formula becomes unreliable when triglyceride levels are over 400, in which case LDL must be directly measured.
Another calculation gives the cholesterol ratio, which is the total cholesterol divided by the HDL level. According to the American Heart Association, the level of total cholesterol should not be more than five times the level of good cholesterol. This may be expressed as the ratio 5:1.
A ratio of 3.5:1 is considered optimal. The goal is to keep the ratio below 5:1. Anything over 5:1 indicates a possibly unhealthy balance of LDL cholesterol in the blood. Regardless of total cholesterol, experts generally recommend that the level of HDL cholesterol should be at least 40 mg/dL in men and at least 45 mg/dL in women.
Low total cholesterol (below 160) is not directly harmful to the human body but could indicate the presence of other medical conditions that may require attention.
These medical conditions include:
Hyperthyroidism. An overactive thyroid gland that leads to an excess of thyroid hormone in the body.
Malnutrition. Inadequate nutrition that may be caused by an unbalanced diet or a condition in which the body has difficulty digesting or absorbing nutrients from food (malabsorption).
Pernicious anemia. A type of anemia (red blood cell deficiency) caused by the lack of a substance in the body needed to absorb vitamin B-12.
Sepsis. A serious bacterial infection that has spread to the blood.
LDL and higher-risk patients
Treatment for high cholesterol generally centers on reducing low-density lipoproteins (LDL). For higher-risk patients, goals for LDL levels are set based on each patient’s risk category.
These therapeutic goals are as follows (in milligrams per deciliter [mg/dL]):
LDL Cholesterol (Higher-risk patients)
Primary Therapeutic LDL Goals
Secondary Therapeutic LDL Goals
Less than 100 mg/dL
Less than 70 mg/dL
Less than 100 mg/dL
Less than 130 mg/dL
Less than 100 mg/dL
Less than 160 mg/dL
Less than 130 mg/dL
A therapeutic goal is the target that physicians hope to reach through therapies to lower their patients’ LDL. Such therapy usually includes lifestyle changes (e.g., diet and exercise) and the use of cholesterol reducing medications. The two stages of therapeutic goals (primary and secondary) give physicians the option of a lower goal for some patients.
Frequency of cholesterol screening
Regular cholesterol screenings are important. The National Cholesterol Education Program recommends that both males and females 20 years of age and older have a “lipid profile” (or cholesterol test) every five years. Regular cholesterol screenings are particularly important for people who have risk factors such as diabetes, obesity or a family history of cardiovascular disease. Such higher-risk individuals, and people over age 65, may be screened more frequently.
Even children can benefit from having their cholesterol checked because it is one way to identify factors that may adversely affect their heart health as they grow. It has been reported that approximately 50 million children in the United States have high cholesterol levels, which is defined as total cholesterol of 200 milligrams per deciliter (mg/dL).
Total Cholesterol (mg/dL)
LDL Cholesterol (mg/dL)
Less than 170 mg/dL
Less than 110 mg/dL
200 mg/dL or greater
130 mg/dL or greater
However, the U.S. Preventative Services Task Force does not encourage the routine screening of all young children because coronary artery disease tends to begin later in life. Furthermore, starting young children on medication to treat high cholesterol may be more of a risk than the early plaque buildup it is meant to prevent.
Cholesterol screening is fast and relatively painless. Blood is drawn from a vein or through a fingertip “prick test.” Regular screenings are the first line of defense against developing high cholesterol levels. If triglyceride levels are going to be measured, test participants will be asked to stop eating or drinking for approximately nine hours prior to the screening.
This cholesterol screening is only an approximate indication of one’s cholesterol level. Even under normal conditions, the test results may be higher or lower than a person’s actual cholesterol levels by about 14 percent. Also, test results can vary quite a bit even when repeated over a short period of time. Therefore, many physicians will provide results as a cholesterol range (e.g., 150 to 160) rather than an exact number.
Gender differences related to cholesterol
Women benefit from cholesterol-lowering activities as much as men do. Beyond age 45, a greater percentage of women have high cholesterol levels than men, and heart disease has emerged as the leading cause of death among women. It has also been shown that HDL levels tend to drop in women who have just given birth, and that this reduction can continue for as long as 10 years. However, women are far less likely to seek or receive treatment for high cholesterol.
Studies have suggested that high LDL levels are not as significant a risk factor for women as for men. Researchers suggest that apolipoprotein B (apoB), a protein found in low-density lipoproteins, is the best cholesterol-related predictor of coronary artery disease for women (recent studies find that apoB is an equally useful “marker” for men as well).
As gender-specific research continues, women will probably see an increased availability of information and protocols for monitoring their cholesterol levels.
Cholesterol lowering tablets
This works by lowering the blood cholesterol, the triglyceride level, or both. There is now overwhelming evidence that lowering the blood cholesterol by diet and/or drugs will reduce the chances of patients developing coronary artery disease.Cholesterol lowering tablets are not a substitute for a low fat diet. There are a number of groups of these drugs.
Questions for your doctor
Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to cholesterol:
What is my LDL? My HDL? My triglyceride level? My cholesterol ratio?
What factors are likely contributing to my cholesterol levels?
Based on all of my risk factors, what is my 10-year risk of experiencing a cardiovascular event?
What are my ideal cholesterol levels?
What immediate steps can I take to reduce my LDL and raise my HDL?
Am I candidate for cholesterol-lowering medications, such as statins?
If I start taking statins, will I be on them for life?
Are there any dietary supplements that might help lower my cholesterol? Any I should avoid?
Will exercise help lower my cholesterol?
What if lifestyle changes and medications don't lower my cholesterol? What is the next step?
When should I be tested again for elevated cholesterol levels?
Should I be tested for apolipoprotein a or apolipoprotein b? What about LDL particle size and number?