The test for low-density lipoprotein cholesterol (LDL-C) is used as part of a lipid profile to predict an individual's risk of developing heart disease and to help make decisions about what treatment may be needed if there is borderline or high risk. It may also be used to monitor the effectiveness of treatment once it is initiated.

LDL-C is usually not measured directly but is a calculated from the results of the other components of the lipid profile, including total cholesterol, HDL cholesterol (HDL-C), and triglycerides (see Common Questions #3 for the formula). In most cases, the formula provides a good estimate of the LDL-C, but it becomes less accurate with increased triglyceride levels (i.e., above 400 mg/dL). In this case, the only way to accurately determine LDL-C is to measure it directly (see the article on Direct LDL Cholesterol).

Of all the forms of cholesterol in the blood, the LDL-C is considered the most important form in determining risk of heart disease. It is considered to be undesirable and is often call "bad" cholesterol because it deposits excess cholesterol in blood vessel walls and contributes to hardening of the arteries and heart disease. (For more, see the "What is being tested?" section.)

Results of the LDL-C test and other components of the lipid profile are considered along with other known risk factors of heart disease to develop a plan of treatment and follow-up. Treatment options may include lifestyle changes such as diet or exercise programs or lipid-lowering drugs such as statins.

In addition to measuring the amount of LDL-C in blood, a test that measures the number of LDL particles (LDL-P) and/or their size may be useful in helping to determine risk of heart disease in certain people, according to some recent studies. For more on this, see Common Questions #1 and the article on LDL Particle Testing.

Adults

LDL-C levels may be ordered as part a lipid profile when a person has a routine health exam. It is recommended that all adults with no risk factors for heart disease be tested every four to six years.

For people who have one or more major risk factors for heart disease (see below), a fasting lipid profile may be ordered more frequently. It may also be ordered when someone has had a high screening cholesterol result to see if the total cholesterol is high because of too much LDL-C.

Major risk factors for heart disease other than a high LDL-C include:

• Cigarette smoking
• Being overweight or obese
• Unhealthy diet
• Being physically inactive, not getting enough exercise
• Age (males 45 years or older or females 55 years or older)
• High blood pressure (blood pressure of 140/90 or higher or taking high blood pressure medications)
• Family history of premature heart disease (heart disease in a first degree male relative under age 55 or a first degree female relative under age 65)
• Pre-existing coronary heart disease or already having had a heart attack
• Diabetes or prediabetes

[Note: High HDL-C (60 mg/dL or above) is considered a "negative risk factor" and its presence allows the removal of one risk factor from the total.]

Youth

For children and adolescents, routine lipid testing is recommended by the American Academy of Pediatrics once between the ages of 9 and 11 and again between the ages of 17 and 21. Earlier and more frequent screening with a lipid profile is recommended for children and youth who are at increased risk of developing heart disease as adults. Some of the risk factors are similar to those in adults and include a family history of heart disease or health problems such as diabetes, high blood pressure, or being overweight. High-risk children should have their first lipid profile between 2 and 8 years of age. Children younger than 2 years old are too young to be tested.

Monitoring

LDL-C levels may also be ordered at regular intervals to evaluate the success of lipid-lowering lifestyle changes such as diet and exercise or to determine the effectiveness of drug therapy such as statins. Guidelines from the American College of Cardiology and the American Heart Association recommend that adults taking statins have a fasting lipid profile done 4 to 12 weeks after starting therapy and then every 3 to 12 months thereafter to assure that the drug is working.

In general, healthy lipid levels help to maintain a healthy heart and lower the risk of heart attack or stroke. A healthcare practitioner will take into consideration the results of the LDL-C and the other components of a lipid profile as well as other risk factors to help determine a person's overall risk of heart disease, whether treatment is necessary and, if so, which treatment will best help to lower the person's risk.

Adults

In 2002, the National Cholesterol Education Program (NCEP) Adult Treatment Panel III (ATPIII) provided guidelines for evaluating lipid levels and determining treatment. However, in 2013, the American College of Cardiology (ACC) and the American Heart Association (AHA) issued guidelines for adults that made recommendations on who should receive cholesterol-lowing therapy, depending on age, presence of heart disease and/or diabetes, and LDL-C level.

In healthy adults with no heart disease, the decision to treat is based on a risk calculator that takes into account several factors (e.g., age, gender, race, blood pressure, cholesterol level) and determines the risk of having a heart attack or stroke in the next 10 years. A person with a 7.5% or higher risk should be prescribed statins, according to the ACC/AHA guidelines.

Recent guidelines also recommend focusing on a percentage reduction in LDL-C rather than target values to reduce the risk of atherosclerotic cardiovascular disease (ASCVD).

However, use of the updated risk calculator and guidelines remains controversial. Many still use the older guidelines from the NCEP ATP III to evaluate lipid levels and heart disease risk. According to the NCEP, if a person has no other risk factors, an LDL-C level can be evaluated as follows:

• Less than 100 mg/dL (2.59 mmol/L) — Optimal 
• 100-129 mg/dL (2.59-3.34 mmol/L) — Near optimal, above optimal 
• 130-159 mg/dL (3.37-4.12 mmol/L) — Borderline high 
• 160-189 mg/dL (4.15-4.90 mmol/L) — High 
• Greater than 189 mg/dL (4.90 mmol/L) — Very high

Desired goals for LDL-C levels change based on individual risk factors. Lifestyle changes, such as altering diet and exercise, are recommended as treatment to lower elevated levels of LDL-C to target LDL-C values. Certain combinations of LDL-C levels and individual risk factors for heart disease may warrant treatment with cholesterol-lowering drugs, such as statins, in addition to lifestyle changes.

Target values based on risk factors are:

• LDL-C less than 100 mg/dL (2.59 mmol/L) with heart disease or diabetes* 
• LDL-C less than 130 mg/dL (3.37 mmol/L) with 2 or more risk factors (intermediate risk for heart disease) 
• LDL-C less than 160 mg/dL (4.14 mmol/L) with 0 or 1 risk factor (low risk for heart disease)

*Some organizations recommend that LDL-C be less than 70 mg/dL (1.82 mmol/L) if a person has heart disease or has had a heart attack.

Youth

According to the American Academy of Pediatrics, the LDL-C level can be evaluated for youth with no other risk factors as follows:

For children and teens:

• Less than 110 mg/dL (2.85 mmol/L) — Acceptable
• 110-129 mg/dL (2.85-3.34 mmol/L) — Borderline high
• Greater than 130 mg/dL (3.36 mmol/L) — High

For young adults:

• Less than 120 mg/dL (3.10 mmol/L) — Acceptable
• 120-159 mg/dL (3.10-4.11 mmol/L) — Borderline high
• Greater than 160 mg/dL (4.12 mmol/L) — High

Low levels of LDL cholesterol are not generally a concern and are not monitored. They may be seen in people with an inherited lipoprotein deficiency and in people with hyperthyroidism, infection, inflammation, or cirrhosis.

LDL-C should be measured when a person is not ill. LDL-C is temporarily low during acute illness, immediately following a heart attack, or during stress (like from surgery or an accident). Wait at least six weeks after any illness to have LDL-C measured.

Certain types of prescription drugs may raise or lower LDL-C levels. Inform your healthcare provider of any drugs or supplements that you are taking before testing.

In women, LDL-C usually rises during pregnancy. Women should wait at least six weeks after having a baby to have LDL-C measured.