Direct LDL cholesterol
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
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. Usually, the amount of LDL cholesterol (LDL-C) is calculated using the results of a standard lipid profile. In most cases, this is a good estimate of the LDL-C, but it becomes less accurate with increased triglyceride levels. Direct measurement of LDL-C is less affected by triglycerides and can be used when you are not fasting or when you have significantly elevated triglycerides (above 4.5 mmol/L).
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.
The Test
How is it used?
Measurements of low density lipoprotein cholesterol (LDL-C) are helpful in assessing a patient's risk for heart disease and in following therapy to lower cholesterol. A standard lipid profile consists of total cholesterol, high-density lipoprotein cholesterol (HDL-C), and triglycerides. By applying a formula, the amount of cholesterol present in low-density lipoprotein can be determined, and this calculated value is typically reported as well. When triglycerides are high, the formula no longer applies. 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 patient's blood.
When is it requested?
Direct LDL-C may be specifically ordered when calculation of LDL cholesterol will not be accurate because the patient's triglycerides are significantly elevated. In some laboratories, this test will automatically be run on the same sample if the triglycerides are too high. This saves the doctor an extra step and speeds up the test turn-around time. Some laboratories may choose to use this method for all LDL-C testing.
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 patients with an inherited lipoprotein deficiency and in patients with hyperthyroidism, infection, and inflammation.
Is there anything else I should know?
The direct LDL-C, like calculated LDL-C, should be measured when you are healthy and 'metabolically stable'. Illness, surgery, trauma, a heart attack, sudden weight loss or gain, and pregnancy can all temporarily affect LDL levels.
Common Questions
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Article Sources
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
