LDL cholesterol, short for low-density lipoprotein cholesterol, is the cholesterol carried in the blood by particles that can build up in the walls of arteries. It is often called “bad” cholesterol for that reason. LDL cholesterol is reported as part of a lipid panel. Reports in the United States give it in milligrams per deciliter (mg/dL), while Canada and most other countries use millimoles per liter (mmol/L).
This article explains what the LDL cholesterol test measures and why your result is compared with a personal target rather than only with the reference range. It also explains how the number is usually calculated, what high and low LDL results mean, and what your doctor will likely do next.
The reference range that applies to your result is the one printed on your laboratory report, not the typical ranges shown here. Reference ranges vary between laboratories based on the equipment used, the population tested, and individual factors such as age, sex, and pregnancy status. Always compare your result to the reference range printed on your own report, and discuss any abnormal result with your doctor.
The LDL cholesterol test estimates how much cholesterol your blood carries in low-density lipoprotein particles. Cholesterol is a fatty substance the body needs to build cells and make hormones. Because it doesn’t dissolve in blood, it travels in particles called lipoproteins, and LDL particles carry most of it.
When there are more LDL particles than the body needs, some of them slip into the walls of arteries and become trapped there. Over many years, they help form fatty deposits called plaque, which narrow arteries and can lead to heart attacks and strokes. The higher the LDL level, and the longer it stays high, the more plaque tends to build up.
For most blood tests, the goal is a result within the reference range. LDL cholesterol works differently. Your doctor compares your LDL result with a target chosen for your own risk of heart attack and stroke. Two people with the same LDL can therefore receive different advice.
Your doctor calculates the risk that sets your target from several things they already know about you. Your age, your blood pressure, and whether you smoke are all part of it. Diabetes, kidney disease, and a family history of early heart disease add to it as well. Doctors combine these into a single estimate using a risk calculator. Someone who has already had a heart attack or stroke is at the highest risk of another one, and so has the lowest target.
Targets returned to United States guidance in March 2026, when the American College of Cardiology and the American Heart Association published a new guideline replacing their 2018 version. Typical targets in that guideline are:
The Canadian Cardiovascular Society guidelines, most recently published in 2021, use a similar level of 1.8 mmol/L (70 mg/dL) for people with existing heart disease. They describe it as a threshold for adding more treatment rather than as a target to aim for. Your doctor will tell you which number applies to you and why.
The LDL cholesterol test uses a blood sample drawn from a vein, usually as part of a lipid panel. Fasting is usually not needed because LDL cholesterol changes only slightly after a normal meal, typically by about 8 mg/dL (0.2 mmol/L). Some laboratories still require fasting, so follow the instructions you were given.
Most laboratories do not measure LDL cholesterol directly. They calculate it from the total cholesterol, HDL cholesterol, and triglycerides measured on the same sample. The oldest formula, the Friedewald equation, tends to underestimate LDL when it is low or when triglycerides are high. The 2026 ACC/AHA guideline recommends newer formulas, called the Martin-Hopkins and Sampson equations, which are more accurate in those situations.
When triglycerides are very high, the lab may not report a calculated LDL at all. In that case, the laboratory may measure LDL directly, or your report may show a note explaining why the value is missing.
Your LDL cholesterol result is read against your personal target and against the reference range printed on your own report. Many United States reports still print categories first set by the National Cholesterol Education Program in 2001, which are approximately:
LDL cholesterol depends partly on the genes you inherited and partly on diet, weight, and other medical conditions. Knowing which of these is driving a high result helps your doctor decide what else to check and how to treat it.
Conditions and factors that can raise LDL cholesterol include:
Conditions and factors that can lower LDL cholesterol include:
LDL cholesterol is interpreted alongside the other parts of the lipid panel and a few related tests.
After an LDL cholesterol test, your doctor compares the result with your target and looks at your overall risk. If your LDL is above your target, the usual first step is a conversation about diet, physical activity, and smoking. Your doctor often discusses cholesterol-lowering medication at the same visit, and that decision depends on your overall risk rather than the LDL number alone.
If you start or change treatment, your doctor usually repeats the LDL test in about one to three months to see how well it is working. After that, they check it periodically. A very high LDL may lead your doctor to ask about your family history and to suggest testing close relatives for familial hypercholesterolemia.
High LDL cholesterol does not cause symptoms on its own. Chest pain or pressure, sudden weakness, or difficulty speaking need emergency care, regardless of your LDL result.