At a Glance
Why Get Tested?
To determine risk of developing heart disease
When to Get Tested?
As part of a regular examination with a cholesterol test or lipid profile or if your total cholesterol is high
Sample Required?
A blood sample taken from a vein in the arm or from a fingerstick
The Test Sample
What is being tested?
LDL is a type of lipoprotein that carries cholesterol in the blood. LDL is considered to be undesirable because it deposits excess cholesterol in the walls of blood vessels and contributes to 'hardening of the arteries' and heart disease. Hence LDL cholesterol is often termed 'bad' cholesterol. The test for LDL measures the amount of LDL cholesterol in blood.
How is the sample collected for testing?
The test for LDL cholesterol uses a blood sample. Most often, the blood sample is collected by venipuncture (using a needle to collect blood from 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.
The Test
How is it used?
The test for LDL is used to predict your risk of developing heart disease. Of all the forms of cholesterol in the blood, the LDL cholesterol is considered the most important form in determining risk of heart disease. Treatment decisions are often based on LDL values.
When is it requested?
LDL levels are ordered as part a lipid profile, along with total cholesterol, HDL, and triglycerides. This profile may be used as a screening test in a healthy person as part of a routine physical examination. A lipid profile may be requested on someone who has had a high screening cholesterol to see if the total cholesterol is high because of too much LDL.
What does the test result mean?
Elevated levels of LDL indicate risk for heart disease. Treatment (with diet or drugs) for high LDL aims to lower LDL to a target value of less than 3 mmol/L.
This is especially important if you have other risk factors for heart disease. Risk factors include cigarette smoking, hypertension, low HDL (< 1 mmol/L), family history, age (male 55 or older; female 65 or older), being overweight, and failure to exercise regularly.
Is there anything else I should know?
Measurement of LDL generally requires a 12-hour fast—meaning that you must not eat or drink anything that has calories for 12 hours before your blood is collected. This is because LDL is usually calculated from the results of other tests, including triglycerides, that require fasting. This result may be reported as 'calculated LDL'. Some laboratories can measure LDL directly using a special technology and fasting is not necessary. This test is usually called 'direct LDL'.
LDL cholesterol should be measured when a person is healthy. LDL cholesterol is temporarily low during acute illness, immediately following a heart attack, or during stress (like from surgery or an accident). You should wait at least six weeks after any illness to have LDL cholesterol measured.
In women, cholesterol is high during pregnancy. Women should wait at least six weeks after the baby is born to have LDL cholesterol measured.
Common Questions
Ask a Laboratory Scientist
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.
