Tests guide

LDL Cholesterol

LDL cholesterol is often called "bad" cholesterol because higher levels are linked to buildup in the arteries. This guide explains what LDL is and how its test results are generally described.

Last updated 4 sources

At a Glance

  • LDL stands for low-density lipoprotein, a particle that carries cholesterol through the blood.
  • Higher LDL levels over time are associated with plaque buildup in arteries (atherosclerosis) and a higher risk of heart attack and stroke.
  • LDL is usually measured as part of a lipid panel (cholesterol blood test).
  • In the US, results are reported in milligrams per deciliter (mg/dL); many other countries use millimoles per liter (mmol/L).
  • There is no single "right" LDL number for everyone; clinicians consider it together with a person's overall heart risk.

What It Is

Cholesterol is a waxy, fat-like substance the body needs to build cells and make certain hormones. Because it does not dissolve in blood, it travels in particles called lipoproteins. LDL is one of the main types.

When there is more LDL in the blood than the body uses, cholesterol can collect in artery walls as part of plaque. Over years, plaque can narrow arteries or break open and trigger a clot.

LDL levels are influenced by genetics, diet, physical activity, body weight, other health conditions, and some medications. Some people have inherited conditions, such as familial hypercholesterolemia, that cause very high LDL from a young age.

Common Terminology

LDL-C
Shorthand for LDL cholesterol, the amount of cholesterol carried in LDL particles.
Lipoprotein
A particle made of fat and protein that carries cholesterol and triglycerides in the blood.
Atherosclerosis
Hardening and narrowing of the arteries caused by plaque buildup.
Calculated LDL
An LDL value estimated with a formula from total cholesterol, HDL, and triglycerides, rather than measured directly.
Direct LDL
An LDL value measured directly in the lab, sometimes used when triglycerides are high.
Familial hypercholesterolemia
An inherited condition that causes high LDL levels, often starting in childhood.

Why the Test Is Done

LDL testing is a standard part of heart health screening.

  • To screen adults for high cholesterol, which usually causes no symptoms.
  • To help estimate overall risk of heart disease and stroke along with other factors.
  • To follow LDL levels over time in people with known high cholesterol or heart disease.
  • To check how LDL has changed after lifestyle changes or medication.
  • To screen children or relatives when there is a family history of very high cholesterol or early heart disease.

What the Results Generally Describe

A commonly cited set of adult LDL categories (in mg/dL) is listed below as general reference. Labs and guidelines differ, current guidelines focus on overall risk rather than one target, and a clinician interprets individual results.

  • Below 100 mg/dL: often described as optimal for many adults.
  • 100 to 129 mg/dL: often described as near optimal or above optimal.
  • 130 to 159 mg/dL: often described as borderline high.
  • 160 to 189 mg/dL: often described as high.
  • 190 mg/dL or higher: often described as very high and may prompt evaluation for inherited causes.
  • People with existing heart disease, diabetes, or other risk factors may be given lower goals by their care team.

How the Test Is Done

LDL is measured from a blood sample.

  • Blood is usually drawn from a vein in the arm and sent to a laboratory.
  • LDL is most often calculated from the other lipid panel results using a formula.
  • Some labs measure LDL directly, especially when triglycerides are high and the formula is less reliable.
  • Finger-stick tests are available in some pharmacies and screening events.

Preparation and What to Expect

The test itself is quick and routine.

  • Many labs no longer require fasting for a standard cholesterol test, but some still ask for 9 to 12 hours without food; the ordering office gives instructions.
  • A blood draw takes a few minutes and may cause brief stinging and minor bruising.
  • Recent illness, pregnancy, and some medications can affect cholesterol levels temporarily.
  • Results are often available within a day or a few days.

When Results Are Discussed With a Clinician

Health professionals generally look at LDL alongside other numbers and risk factors.

  • Results are commonly reviewed together with HDL, triglycerides, blood pressure, smoking status, diabetes, age, and family history.
  • Very high LDL is often discussed in terms of possible inherited causes and family screening.
  • Changes in LDL over time are often more informative than a single result.
  • Results may be compared with earlier tests to see trends.

Questions to Ask a Healthcare Professional

General questions people often find useful to bring to an appointment:

  • Was my LDL calculated or measured directly?
  • How is LDL considered together with my other risk factors?
  • Is fasting needed before my cholesterol test?
  • How often is LDL generally rechecked?
  • Does family history make inherited high cholesterol worth looking into?
  • Are there other tests, like non-HDL cholesterol or lipoprotein(a), that are sometimes considered?

Sources

This guide was written in plain language from the following authoritative references.

  1. LDL: The "Bad" Cholesterol — MedlinePlus (U.S. National Library of Medicine)
  2. Cholesterol Levels — MedlinePlus (U.S. National Library of Medicine)
  3. Blood Cholesterol — National Heart, Lung, and Blood Institute (NIH)
  4. Cholesterol — Centers for Disease Control and Prevention (CDC)

Last updated October 8, 2026. FreeDoc guides are general educational information and are not a substitute for care from a qualified professional.