Dr Leigh Martens

General Practitioner

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Release Version: Beta

Blood-tests Explained


Disclaimer:

This website is intended to assist with patient education and should not be used as a diagnostic, treatment or prescription service, forum or platform. Always consult your own healthcare practitioner for a more personalised and detailed opinion

Direct LDL-C


At a Glance

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.

The Test Sample

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.

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

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

The Test

How is it used?

Low density lipoprotein cholesterol (LDL-C) values are typically used either to assess a person's risk forheart 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.