To determine your risk of developing heart disease; to monitor effectiveness of lipid-lowering therapy
Screening: as part of a health exam with a lipid panel; every four to six years in adults with no risk factors for heart disease; youth should be tested at least once between the ages of 9 and 11 and once again between the ages of 17 and 21
A blood sample drawn from a vein in your arm or from a fingerstick
Laboratory tests for LDL-C typically require a 9 to 12-hour fast, but your healthcare practitioner may decide that you may be tested without fasting. In particular, youths (ages 2 to 24) without risk factors may have testing done without fasting. Follow any instructions you are given and tell the person drawing your blood whether or not you have fasted.
Low-density lipoprotein is a type of lipoprotein that consists of cholesterol (LDL cholesterol, LDL-C) and similar substances with a small amount of protein. Testing for LDL-C often involves using a formula to calculate the amount of LDL-C in blood based on results of a lipid panel. Sometimes, LDL-C is measured directly.
Monitoring and maintaining appropriate levels of cholesterol and other lipids is important for staying healthy. A diet high in saturated fats and trans unsaturated fats (trans fats), or an inherited predisposition can result in a high level of cholesterol in the blood. The extra cholesterol may be deposited in plaques on the walls of blood vessels. Plaques can narrow or eventually block the opening of blood vessels, leading to hardening of the arteries (atherosclerosis) and increased risk of numerous health problems, including heart disease and stroke.
High LDL-C is considered to be undesirable and LDL-C is often called "bad" cholesterol because it is associated with cholesterol plaques, atheroslcerosis, and heart disease. This is in contrast to high-density lipoproteins (HDL) that tend to transport cholesterol from the arteries to the liver. High HDL-C is thought to protect against heart disease and so it is often called "good" cholesterol.
- How is the test used?
The test for low-density lipoprotein cholesterol (LDL-C) is used as part of a lipid panel to estimate your likelihood of developing heart disease. If you have borderline, intermediate or high risk, results of the LDL-C test and other components of the lipid panel 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. LDL-C test may be also used to monitor whether treatment has been effective in lowering cholesterol levels.
LDL-C is often not measured directly but is instead calculated from other components of the lipid panel, including total cholesterol, HDL cholesterol (HDL-C), and triglycerides (see below for the most commonly-used formula). In most cases, this calculation provides a good estimate of LDL-C, but it becomes less accurate in patients with triglyceride levels above 400 mg/dL, severe cirrhosis, and other conditions. For these individuals, accurate determination of LDL-C can be done with direct LDL-C tests or special testing techniques (e.g., beta quantification).
- When is it ordered?
Many health organizations recommend that all adults with no other risk factors for heart disease be tested with an LDL-C test as part of a fasting lipid panel every four to six years.
If you have risk factors for heart disease (see below) or if previous testing showed that you had undesirable results, more frequent testing with a fasting lipid panel is recommended.
Examples of risk factors for heart disease 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 a previous heart attack
- Diabetes or prediabetes
Children, teens and young adults (ages 2 to 24 years old) with no risk factors should have a lipid panel done once between the ages of 9 and 11 and again between the ages of 17 and 21, according to the American Academy of Pediatrics (AAP).
Youths with an increased risk of heart disease as adults should have earlier and more frequent screening with lipid panels. 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 be tested between 2 and 8 years old with a fasting lipid panel, according to the AAP. Children younger than 2 years old are too young to be tested.
LDL-C levels, either alone or as part of lipid panels, 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.
- What does the test result mean?
In general, healthy lipid levels help to maintain a healthy heart and lower the risk of heart attack or stroke. Your healthcare practitioner will take into consideration the results of the LDL-C and the other components of a lipid panel as well as other risk factors to help determine your overall risk of heart disease, whether treatment is necessary and, if so, which treatment will best help to lower your risk.
Health organizations have different recommendations for treatment based on your predicted cardiovascular disease (CVD) risk.
Current guidelines from the American College of Cardiology (ACC) and the American Heart Association (AHA) recommend that a risk calculator be used to determine your 10-year risk of CVD if you are age 40 to 75 and do not have heart disease. Many factors are considered in the calculation, including total cholesterol, LDL-C, HDL-C, age, gender, race, blood pressure, diabetes, and smoking.
ACC and AHA recommend treatment with statins if you:
- Have heart disease (diagnosed by medical history, imaging, etc.)
- Have LDL-C greater than 190 mg/dL (4.90 mmol/L)
- Are age 40 to 75 years with diabetes and LDL-C 70-189 mg/dL (1.81-4.90 mmol/L)
- Are age 40 to 75 years old with LDL-C level between 70-189 mg/dL (1.81-4.90 mmol/L) and 10-year risk of developing heart disease of greater than 7%
The U.S. Preventive Services Task Force (USPSTF) makes recommendations on the use of statins for treatment in adults ages 40 to 75 with no history of heart disease, based on risk factors (i.e., LDL-C greater than 130 mg/dL [3.37 mmol/L], HDL-C less than 40 mg/dL [1.0 mmol/L], diabetes, blood pressure, smoking) and the use of the risk calculator.
- If you have one or more risk factors and a calculated 10-year CVD event risk of 10% or greater, USPSTF recommends the use of a low-to-moderate dose statin.
- If you have one or more risk factors and your calculated 10-year CVD event risk is 7.5% to 10%, USPSTF says your healthcare practitioner may choose to offer a low-to-moderate dose statin. This is because the probability that you will have a CVD event is lower, so the benefit of statin is likely to be smaller.
According to the USPSTF, there is not currently enough evidence to evaluate the utility of screening adults ages 21 to 39 for unhealthy lipid levels, or to assess the benefits and risks of statin use in adults 76 years or older with no history of CVD.
Use of the risk calculator and ACC/AHA guidelines remains controversial and is evolving as more data become available. Some say that the current risk calculator can overestimate risk. Many still use the older guidelines (2002) from the NCEP Adult Treatment Panel (ATP) III to evaluate LDL-C levels and heart disease risk, as summarized below.
Optimal Near/Above Optimal Borderline High High Very High Less than 100 mg/dL (2.59 mmol/L); with CVD or diabetes: less than 70 mg/dL (1.81 mmol/L) 100-129 mg/dL (2.59-3.34 mmol/L) 130-159 mg/dL (3.37-4.12 mmol/L) 160-189 mg/dL (4.15-4.90 mmol/L) Greater than 190 mg/dL (4.90 mmol/L)
According to NCEP ATP III guidelines, if you have LDL-C above the following target values and risk factors (e.g., family history, cigarette smoking, diabetes, high blood pressure), you require treatment.
The target LDL-C values are:
- Less than 100 mg/dL (2.59 mmol/L) if you have heart disease or diabetes [and ideally less than 70 mg/dL [1.81 mmol/L)]
- Less than 130 mg/dL (3.37 mmol/L) if you have 2 or more risk factors
- Less than 160 mg/dL (4.14 mmol/L) if you have 0 or 1 risk factor
According to the American Academy of Pediatrics, the LDL-C level can be evaluated for youth with no other risk factors as follows:
Acceptable Borderline High Children and Teens (ages 2 to 18) Less than 110 mg/dL (2.85 mmol/L) 110-129 mg/dL (2.85-3.34 mmol/L) Greater than or equal to 130 mg/dL (3.36 mmol/L) Young Adults (ages 19 to 24) Less than 120 mg/dL (3.10 mmol/L) 120-159 mg/dL 3.10-4.11 mmol/L) Greater than or equal to 160 mg/dL (4.12 mmol/L)
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.
- What treatments are recommended for high LDL-C levels?
Maintaining a healthy lifestyle is an important part of heart health and in treating high LDL-C. This may mean you will need to change your lifestyle, specifically by adopting a diet low in saturated fat and trans unsaturated fats (trans fats), avoiding smoking, controlling high blood pressure and diabetes, achieving and maintaining desirable body weight, and getting regular exercise. You may be referred to a dietician for advice in making dietary changes.
Your healthcare practitioner will talk to you about risks and benefits of lipid-lowering therapy, based on your history, health risks, the results of your lipid panel, and possibly your calculated risk for CVD. Statins are generally recommended as a first choice for lowering LDL-C. You may be prescribed one of these. Your LDL-C will be checked at regular intervals to make sure that the drug is working. If your LDL-C is above target levels, your healthcare practitioner may increase the amount of drug, change drugs, or possibly add a second drug.
- Can I test my LDL cholesterol at home?
There are tests available to use at home to measure total cholesterol. You prick your finger and put blood on a piece of paper that will change color based on your cholesterol level (or use your blood and a small device to do the same thing).
There are also kits available that have you collect a blood sample at home and then mail it to a reference laboratory, which will perform a lipid panel and send the results back to you.
- What is the formula used to calculate LDL-C?
The formula most often used by laboratories is called the Freidewald formula, though some research suggests it's not the most accurate formula and some recommend using other formulas instead. The Freidewald formula uses the results from the components of the lipid panel that are measured directly. In the U.S., units are in mg/dL and the formula can only be applied if total triglycerides are less than 400 mg/dL:
LDL cholesterol = Total cholesterol HDL cholesterol (Total triglycerides/5)
- What is a direct LDL cholesterol test?
The direct low-density lipoprotein cholesterol test (direct LDL-C) is an actual measurement of the amount of LDL cholesterol in your blood. Usually, your LDL-C level is calculated using the measured values of the components of a standard lipid panel. In most cases, calculated LDL-C is a good estimate of the LDL-C, but it becomes less accurate with increasing triglyceride levels. A direct LDL-C may be ordered by your healthcare practitioner when prior test results have indicated high triglycerides. In some laboratories, the direct LDL-C test will automatically be performed when the triglyceride levels are too high to calculate LDL-C.
- What is LDL particle testing?
LDL particle testing (LDL-P) is additional testing that may be used to help estimate your risk of cardiovascular disease (CVD). This is a test that measures the number of LDL particles, rather than measuring the amount of LDL cholesterol. For many people, the LDL-C test is a good indicator of risk of CVD, but research has found that some people with healthy levels of LDL-C still have increased risk of CVD. Similarly, individuals with some chronic conditions such as diabetes may have increased risk even though their LDL-C is at a healthy level. For these populations, it has been suggested that the number of LDL particles and/or their size might be an additional factor to consider when determining their CVD risk. For more on this, see the article on LDL Particle Testing.
- Is there anything else I should know?
LDL-C should be measured when you are 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.