Direct LDL Cholesterol

Direct LDL cholesterol testing measures the amount of cholesterol found inside low-density lipoproteins (LDL) in a sample of blood. LDL cholesterol is known as a type of “bad” cholesterol because it can build up in the blood vessels such as arteries and increase the risk of stroke, heart disease, and heart attack.

In most lipid panels, LDL cholesterol is estimated using an equation involving other cholesterol measurements. A direct LDL cholesterol test is distinct in that it directly measures LDL cholesterol in the blood.

Direct LDL cholesterol tests can be a tool for early detection of cardiovascular disease risk and may also be used for cholesterol monitoring and diagnosis of various health conditions.

Purpose of the test

The purpose of a direct LDL cholesterol test is to determine the amount of “bad” LDL cholesterol in the blood. Assessing LDL cholesterol levels can be involved in health screening, monitoring, and diagnosis.

• Screening is looking for evidence of health problems before any symptoms are present. Evaluating LDL cholesterol levels can play an important role in screening for cardiovascular disease risk. Early detection of high levels of LDL cholesterol can help identify people who are more likely to develop heart disease or experience a heart attack or stroke.
• Monitoring is checking how a condition progresses over time. LDL cholesterol may be tested periodically to assess cardiovascular health. LDL cholesterol testing can also be used to see if treatment to lower LDL cholesterol has been effective.
• Diagnosis is the process of identifying the cause of health problems after symptoms have started. A direct LDL cholesterol test may be part of the diagnostic process for cardiovascular problems. Cholesterol levels may also be tested for certain conditions that affect the pancreas, liver, and thyroid.

What does the test measure?

A direct LDL cholesterol test measures the amount of cholesterol that is found inside of low-density lipoproteins (LDL) in a sample of blood.

Cholesterol is a waxy substance that contributes to important cell functions. Lipoproteins are particles made of fat and protein that transport cholesterol in the blood, allowing it to move through the body. Although cholesterol is necessary for normal cell activity, having too much cholesterol can have negative health effects.

Cholesterol is categorized into different types by the kind of lipoprotein particle that carries it. LDL cholesterol, which is cholesterol transported inside LDL particles, is referred to as a “bad” cholesterol because it can accumulate in the arteries and heighten the risk of heart attack, heart disease, and stroke.

When should I get a direct LDL cholesterol test?

Direct measurement of LDL cholesterol is not a routine cholesterol test. Instead, it is most often used if you need a cholesterol test but may have high levels of fat molecules called triglycerides.

High triglycerides can invalidate the formula used to calculate LDL cholesterol. As a result, the doctor may recommend a direct LDL cholesterol test if you had high levels of triglycerides on a prior test or if you have risk factors for high triglycerides. Conditions associated with high triglycerides levels include:

• Type 2 diabetes
• Obesity
• Use of certain medications
• Significant alcohol consumption

If you previously had cholesterol testing with a direct LDL cholesterol test, your doctor may recommend that any future screening or monitoring also be done with a direct LDL cholesterol measurement. Keeping the test method consistent makes it easier to compare results of different tests.

How to get tested

A direct LDL cholesterol test is ordered by a doctor and performed with a blood draw in a medical setting like a doctor’s office, laboratory, or hospital.

Can I take the test at home?

Direct LDL cholesterol tests are generally not offered as an at-home test. Although at-home testing kits are available that calculate LDL cholesterol, few or no options exist to directly measure LDL cholesterol with at-home testing.

How much does the test cost?

Various costs can be associated with a direct LDL cholesterol test. These include charges for an office visit, the blood draw procedure, and the laboratory’s analysis.

The exact cost of these charges typically depends on whether you have health insurance and where the testing is performed. Some or all costs may be paid by insurance if the test is ordered by your doctor. Your insurance provider can clarify any expected out-of-pocket costs such as deductibles and copayments.

If you do not have health insurance, you can talk with your doctor or a hospital administrator about the costs of testing for the uninsured. You can also ask about any programs for reduced-cost services or payment plans.

A blood sample is required for a direct LDL cholesterol test. Normally, this blood sample will be taken using a needle during a routine blood draw at a clinic, hospital, laboratory, or doctor’s office.

Before the test

Depending on the laboratory’s requirements, you may need to fast before a direct LDL cholesterol test. If fasting is necessary, you have to avoid consuming any food or drinks besides water for 8 to 12 hours before your blood draw.

Since pretest instructions can vary, you should ask your doctor about fasting and any other preparations and then closely follow their directions.

During the test

A direct LDL cholesterol test requires withdrawing a sample of blood from your arm. This is a routine procedure that occurs while you are seated. A technician or nurse typically ties a band around your upper arm near the bicep, which increases the blood in your veins.

An antiseptic wipe is used to clean the skin close to a vein, and then the nurse or technician inserts a needle into the vein to collect a vial of blood. Blood is usually taken from a vein on the inside of your elbow.

The entire procedure normally lasts less than a few minutes. You may feel a stinging sensation when the needle is inserted and removed.

After the test

After your blood has been drawn, a bandage may be placed over the puncture site to apply pressure and make sure that any bleeding stops quickly.

If you were told to fast before the test, you can eat once the test is complete. For this reason, you may want to bring a snack to the appointment.

You can generally return to normal activities after blood is withdrawn. Bruising or pain may occur in your arm, but these effects typically go away quickly.

Receiving test results

Results from a direct LDL cholesterol test are often available within several business days after your blood draw. The results may be provided to you by your doctor during a phone call or follow-up visit. Results can also be delivered with a test report delivered by mail or through an online health portal.

Interpreting test results

Your direct LDL cholesterol level is normally listed in milligrams per deciliter (mg/dL) of blood, although some labs provide a measurement in millimoles per liter (mmol/L).

In addition to your LDL cholesterol level, the test report will show the reference range used to interpret your test result. The reference range shows LDL cholesterol levels that the lab considers to be normal. You should look carefully at this reference range because it is specific to the laboratory that performed your test.

In general, it is desirable to have LDL cholesterol levels below 100 mg/dL. High levels of LDL cholesterol can lead to a condition called arteriosclerosis. Arteriosclerosis is an accumulation of plaque in the arteries and can contribute to cardiovascular diseases like coronary heart disease, heart attack, and stroke.

It is important to remember, though, that cholesterol numbers are evaluated within the context of your overall health. Your doctor will also consider your age, sex, family health history, levels of other types of cholesterol, and additional risk factors for cardiovascular disease. Your current LDL cholesterol level may also be compared to your LDL cholesterol level on prior tests.

Careful interpretation of a direct LDL cholesterol test by your doctor is especially important because standard guidelines about managing high cholesterol levels are based on studies that used calculated LDL cholesterol. A doctor is in the best position to account for these factors, explain the significance of your direct LDL cholesterol test, and discuss whether any treatment is appropriate to modify your cardiovascular disease risk.

Very low levels of LDL cholesterol are uncommon but can occur with certain health conditions. When low LDL cholesterol is detected, further tests are typically needed to determine its cause.

Are test results accurate?

Direct LDL cholesterol tests provide increased accuracy in specific situations. For patients with high levels of triglycerides, direct measurement of LDL cholesterol is considerably more accurate than calculating LDL cholesterol.

Some factors that may impact direct LDL cholesterol test results include:

• Active illness: Cholesterol levels can change in response to an acute illness or infection, so testing done during this time may not accurately represent normal levels. Accordingly, cholesterol tests are often postponed if you are currently sick.
• Some blood disorders: Proteins in the blood that are associated with certain blood disorders can alter levels of LDL cholesterol.

Do I need follow-up tests?

The need for follow-up tests is based on your direct LDL cholesterol measurement and other factors specific to your situation. Additional tests of cholesterol or cardiovascular disease risk may be appropriate in some circumstances, or your doctor may suggest taking another direct LDL cholesterol test in the future.

Questions for your doctor about test results

When you receive the results from a direct LDL cholesterol test, some of these questions may be helpful to bring up with your doctor:

• What was my measured LDL cholesterol level?
• Was my LDL cholesterol normal?
• Do I have other risk factors for cardiovascular disease?
• Do you recommend any additional tests?
• Should I take another direct LDL cholesterol test in the future?
• Do you recommend any treatments to improve my cardiovascular health?

A wide range of tests are available to analyze cholesterol in the blood and assess cardiovascular disease risk. Because there are multiple types of cholesterol and test methods, it is common to have questions about these different tests.

The following sections provide more specific information about how direct LDL cholesterol tests compare to several related tests.

Comparing and contrasting a direct LDL cholesterol test and a calculated LDL cholesterol test

A key difference in LDL cholesterol testing is that a direct LDL cholesterol test measures LDL cholesterol specifically while most other tests calculate LDL cholesterol with a mathematical formula.

For standard cholesterol tests like a lipid panel, LDL cholesterol is estimated with a formula based on levels of total cholesterol, high-density lipoprotein (HDL) cholesterol, and triglycerides.

In most cases, a calculated LDL cholesterol level is accurate enough to assess cardiovascular disease risk. However, the formula can’t be used if you have high levels of triglycerides. For those patients direct LDL cholesterol measurements are considered the test of choice.

Both direct and calculated LDL cholesterol tests analyze a blood sample and can be used for screening, monitoring, and diagnosis. However, the choice of test must be tailored for the patient in order to obtain the most accurate result.

Most treatment guidelines for high levels of LDL cholesterol are based upon studies that focused on calculated LDL cholesterol. As a result, the interpretation of direct and calculated LDL cholesterol levels may have some variation that depends on a patient’s individual circumstances.

When multiple LDL cholesterol tests are performed over time, it is generally recommended to use the same type of test so that results can be more appropriately compared.

Comparing and contrasting a direct LDL cholesterol test and a lipid panel

A lipid panel includes LDL cholesterol and additional tests. The standard lipid panel measures total cholesterol, HDL cholesterol, and triglycerides. A special formula is then used to calculate LDL cholesterol.

A lipid panel test is routinely prescribed and used much more frequently than direct LDL cholesterol testing. However, it only provides calculated LDL cholesterol results up to a certain level of triglycerides. Once triglycerides levels exceed this cut-off, direct LDL measurements are recommended to obtain accurate LDL cholesterol results.

Comparing and contrasting a direct LDL cholesterol test and a total cholesterol test

A total cholesterol test measures the sum of all kinds of cholesterol in a blood sample. In this way, total cholesterol includes the amount of “good” HDL cholesterol as well as “bad” types of cholesterol, including LDL cholesterol.

A test of total cholesterol alone does not measure how much LDL cholesterol is present. If a total cholesterol test includes a measurement of HDL cholesterol, it may enable a calculated estimate of LDL cholesterol.

Comparing and contrasting a direct LDL cholesterol test and a non-HDL cholesterol test

A non-HDL cholesterol test uses a formula to estimate the levels of all types of “bad” cholesterol, including cholesterol inside low-density lipoproteins, intermediate-density lipoproteins, very low-density lipoproteins, and lipoprotein (a) particles.

Calculating non-HDL cholesterol requires measuring total cholesterol and HDL cholesterol. The amount of HDL cholesterol is then subtracted from total cholesterol.

Unlike a direct LDL cholesterol test, a non-HDL cholesterol test does not provide a specific result for LDL cholesterol. In addition, non-HDL cholesterol levels are calculated, which is in contrast to a direct LDL cholesterol test that involves an actual measurement of LDL cholesterol by the laboratory.

While non-HDL cholesterol can be a useful tool for assessing cardiovascular disease risk, most patient care guidelines focus on LDL cholesterol levels.

Comparing and contrasting a direct LDL cholesterol test and a lipoprotein (a) test

Lipoprotein (a) is not a type of cholesterol. Instead, it is a specific kind of particle that can carry cholesterol. Research has found that the amount of lipoprotein (a) particles is an independent risk factor that can contribute to cardiovascular disease.

Lipoprotein (a) levels may be a consideration when determining the optimal medical approach for people with elevated levels of LDL cholesterol.