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.

Direct LDL-C is ordered whenever 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.

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.

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.