Direct LDL Cholesterol
A blood sample taken from a vein in your arm
No test preparation is needed. Your doctor might recommend that you fast (water only) for 14 hours prior to the test so that other related substances can be measured in the same sample.
The direct low-density lipoprotein cholesterol test (direct LDL-C) measures the amount of LDL cholesterol, sometimes called “bad” cholesterol, in the blood. Elevated concentrations are associated with increased risk of atherosclerosis and heart disease. 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 concentrations (greater than 4 mmol/L) 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.
How is it used?
Measurement of low density lipoprotein cholesterol (LDL-C) is helpful in assessing a patient’s risk of heart disease and in monitoring the response to lipid lowering therapy. 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 alongside the other values. When triglycerides are high, the formula can no longer be used and 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 concentrations in their blood after eating. In either situation, the direct LDL-C test can determine the amount of LDL in a patient’s blood.
LDL-C may not be included in all standard lipid profiles, as non-HDL cholesterol is increasingly being used to estimate future cardiovascular risk in many situations rather than LDL-C. Non-HDL cholesterol accounts for other forms of “bad” cholesterol in addition to LDL-C. In some cases both LDL-C and non-HDL cholesterol are reported.
When is it requested?
What does the test result mean?
Elevated concentrations of LDL, as measured with the direct LDL-C test, indicate a greater risk of developing heart disease. Concentrations of LDL-C decrease in response to lipid-lowering lifestyle changes and/or drug therapies indicating a decreased risk of heart disease.
Low concentrations 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?
Why hasn't the Direct LDL-C replaced the calculated LDL-C test?
Are all LDL molecules the same?
No, LDL and other lipoprotein molecules vary in size and density. Patients with a larger percentage of small dense LDL molecules are believed to be at greater risk for developing atherosclerosis than those with a higher percentage of large LDL. Different sizes of lipoprotein molecules can be separated by density (through ultra-centrifugation), by size and electrical charge (through electrophoresis) and by other techniques. The clinical usefulness of these tests is however, still to be proven.