LDL Cholesterol – Understanding Your Blood Test Result

Section Editor: Christopher McCudden Ph.D., DABCC, FADLM, FCACB
October 28, 2026

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.

What does the LDL cholesterol test measure?

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.

Why your LDL cholesterol is compared with a target, not just a reference range

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:

Lower or moderate risk, without heart disease—an LDL below 100 mg/dL (2.6 mmol/L).
High risk, without heart disease.—an LDL below 70 mg/dL (1.8 mmol/L).
Existing heart disease or stroke. An LDL below 70 mg/dL (1.8 mmol/L), or below 55 mg/dL (1.4 mmol/L) for people at very high risk.

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.

How is the LDL cholesterol test performed?

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.

What do LDL cholesterol results mean?

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:

Optimal. Below 100 mg/dL (2.6 mmol/L). For many people, this is the general goal, although high-risk individuals have lower targets.
Near optimal. 100 to 129 mg/dL (2.6 to 3.3 mmol/L).
Borderline high. 130 to 159 mg/dL (3.4 to 4.1 mmol/L). Whether this needs treatment depends on your overall risk.
High. 160 to 189 mg/dL (4.1 to 4.9 mmol/L).
Very high. 190 mg/dL (4.9 mmol/L) or above. A level this high raises the possibility of an inherited cause and usually requires treatment, regardless of other risk factors.
A low LDL. A low result is usually good news. A low LDL reached with cholesterol-lowering medication is not considered a problem.

What conditions and factors can affect LDL cholesterol?

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:

Familial hypercholesterolemia. This inherited condition affects roughly 1 in 250 to 1 in 300 people. It causes very high LDL from birth and raises the risk of heart disease at a young age, which is why relatives are usually tested too.
Diet. Foods high in saturated fat raise LDL in many people, although genes matter more than diet for most.
An underactive thyroid gland. Low thyroid hormone slows LDL removal from the blood, and LDL often falls once the thyroid is treated.
Kidney and liver conditions. Kidney disease that leaks protein into the urine can sharply raise LDL. Liver conditions that slow bile flow can do the same.
Menopause and pregnancy. LDL tends to rise after menopause, and it rises during pregnancy as a normal change.
Some medications. Certain steroid medications and some drugs used after organ transplant can raise LDL.

Conditions and factors that can lower LDL cholesterol include:

Cholesterol-lowering medication. Statins are the most common, and doctors may add other medicines if the target isn’t reached.
An overactive thyroid gland. Excess thyroid hormone speeds LDL removal.
Serious illness. LDL often falls for a few weeks during an infection or after surgery or a heart attack. A result taken at one of those times may not reflect your usual level.
Rare inherited conditions. A few families have very low LDL throughout life.

What other tests are ordered with LDL cholesterol?

LDL cholesterol is interpreted alongside the other parts of the lipid panel and a few related tests.

Total cholesterol, HDL cholesterol, and triglycerides. These are measured on the same sample and are used to calculate LDL.
Non-HDL cholesterol. This is total cholesterol minus HDL cholesterol. It captures all particles that can form plaque and is often used when triglycerides are high.
Apolipoprotein B (apoB). This directly counts plaque-forming particles and may be ordered when the LDL result and the overall picture do not match.
Lipoprotein(a). This inherited risk factor does not respond to diet. Both the 2026 ACC/AHA guideline and the 2021 Canadian guidelines recommend measuring it once in adulthood.
Thyroid, kidney, liver, and blood sugar tests—these check for conditions that raise LDL and for diabetes, which raises cardiovascular risk. See our articles on thyroid function tests and hemoglobin A1c.

What happens after an LDL cholesterol test?

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.

Questions to ask your doctor

What was my LDL cholesterol, and what is my target?
What is my estimated risk of a heart attack or stroke, and how was it worked out?
Was my LDL calculated or measured directly?
Could my triglycerides have affected the LDL result?
Could a thyroid, kidney, or liver condition be raising my LDL?
Could my LDL level mean I have familial hypercholesterolemia, and should my relatives be tested?
Has my lipoprotein(a) ever been measured?
Would diet or exercise changes be enough, or do you recommend medication?
When should I have my LDL checked again?
How does this result compare with my previous LDL results?