Patient Test Information

Direct LDL Cholesterol

Also known as:

Direct LDL-C; Direct LDL; DLDL; LDL D

Formal name:

Direct Low-Density Lipoprotein Cholesterol

Related tests:

LDL Cholesterol; Lipid Profile; Cholesterol; HDL Cholesterol; Triglycerides; Apo B; LDL Particle Testing

Why Get Tested?

To help determine your risk of developing heart disease and to monitor lipid-lowering lifestyle changes and drug therapies; to accurately determine your low-density lipoprotein cholesterol (LDL-C) level when you are not fasting

When to Get Tested?

As a follow-up to a lipid profile if your triglycerides are significantly elevated; at regular intervals to monitor efforts to lower LDL levels

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None; however, your health practitioner may request that you fast.

How is it used?

Low density lipoprotein cholesterol (LDL-C) values are typically used either to assess a person's risk for heart disease or to follow response to therapy to lower cholesterol. A standard lipid profile consists of measured values for total cholesterol, high-density lipoprotein cholesterol (HDL-C), and triglycerides. Using a mathematical equation, the amount of cholesterol present in low-density lipoprotein can be determined from the three measured values. The calculated value for LDL-C is typically reported as part of the lipid profile. When triglycerides are high, the equation is no longer valid. In this situation, the only way to accurately determine LDL-C is to measure it directly.

High triglycerides may be due to a metabolic disorder affecting lipids. However, anyone may have high triglycerides after eating. In either situation, the direct LDL-C test can determine the amount of LDL in a person's blood.

When is it ordered?

Direct LDL-C is ordered whenever calculation of LDL cholesterol will not be accurate because the person's triglycerides are significantly elevated. It may be ordered by a doctor when prior test results have indicated high triglycerides. In some laboratories, this direct LDL test will automatically be performed when the triglyceride levels are too high to calculate LDL-C. This saves the doctor time by not needing to order another test, saves the patient time by not needing to have a second blood sample drawn, and speeds up the time to provide the test result.

What does the test result mean?

Elevated levels of LDL, as measured with the direct LDL-C test, indicate a greater risk of developing heart disease. Decreasing levels show a response to lipid-lowering lifestyle changes and/or drug therapies and indicate a decreased risk of heart disease.

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

Is there anything else I should know?

The direct LDL-C, like calculated LDL-C, should be measured when a person is healthy and "metabolically stable." Illness, surgery, trauma, a heart attack, sudden weight loss or gain, and pregnancy can all temporarily affect LDL levels.

What is being tested?

The direct low-density lipoprotein cholesterol test (direct LDL-C) measures the amount of LDL cholesterol, sometimes called "bad" cholesterol, in the blood. Elevated levels of LDL-C are associated with an increased risk of hardening of the arteries (atherosclerosis) and heart disease. Usually, the amount of LDL-C is calculated using the measured values (cholesterol, HDL-C, and triglycerides) from a standard lipid profile. In most cases, this is a good estimate of the LDL-C, but it becomes less accurate with increasing triglyceride levels. Direct measurement of LDL-C is less affected by triglycerides and can be used when triglycerides are high (above 400 mg/dl).

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed; however, a health practitioner may request fasting.

  1. Why hasn't the Direct LDL-C replaced the calculated LDL-C test?

    Calculated LDL-C is about as accurate as direct LDL-C when triglyceride levels are normal. It can be done at no additional cost when a lipid profile is performed.

  2. Are all LDL molecules the same?

    No, LDL and other lipoprotein molecules vary in size and density. Patients with mostly small, dense LDL molecules are believed to be at greater risk for atherosclerosis than those with mostly large LDL. While it is technically possible to separate the different lipoprotein molecules by density or size and electrical charge, the clinical usefulness of information about the size distribution is unclear.