Calculates LDL from total cholesterol, HDL, and triglycerides.
Source: Friedewald, Levy & Fredrickson, Clin Chem 1972. Unreliable when TG > 4.5 mmol/L (≈400 mg/dL).
What does LDL cholesterol mean?
Low-density lipoprotein (LDL) cholesterol, often called "bad cholesterol", is the primary carrier of cholesterol in the bloodstream. Elevated LDL causes atherosclerosis by depositing cholesterol into arterial walls, forming plaques that narrow and harden vessels over time. This process is a primary driver of heart attack and stroke.
The Friedewald equation (1972) estimates LDL from a standard lipid panel: LDL = Total Cholesterol − HDL − (Triglycerides ÷ 5) in mg/dL. The triglyceride term approximates VLDL cholesterol, which is not directly measured in a routine fasting panel. This approximation breaks down when triglycerides exceed 400 mg/dL (4.5 mmol/L); above that level, a direct LDL measurement is needed.
LDL particles vary in size and density. Small, dense LDL particles are considered more atherogenic than large, buoyant ones. However, routine lipid panels do not distinguish particle size; total LDL-C remains the primary treatment target in most major guidelines.
Multiple factors affect LDL: saturated and trans fats raise it; unsaturated fats, soluble fibre, plant sterols, and statins lower it. Genetic conditions such as familial hypercholesterolaemia cause severely elevated LDL irrespective of diet.
Reference ranges (ACC/AHA 2018)
| Category | LDL (mmol/L) | LDL (mg/dL) |
|---|---|---|
| Optimal | < 2.6 | < 100 |
| Near optimal | 2.6 – 3.3 | 100 – 129 |
| Borderline high | 3.4 – 4.1 | 130 – 159 |
| High | 4.1 – 4.9 | 160 – 189 |
| Very high | ≥ 4.9 | ≥ 190 |
When should you see a doctor?
An LDL above 4.1 mmol/L (160 mg/dL) warrants medical review. An LDL ≥ 4.9 mmol/L (190 mg/dL) may indicate familial hypercholesterolaemia, which typically requires statin therapy regardless of other risk factors. Even lower LDL values may need treatment if you have diabetes, established cardiovascular disease, or high Framingham risk, your overall risk profile matters more than any single number.
Frequently asked questions
What is a healthy LDL cholesterol level?
Current ACC/AHA guidelines consider LDL below 2.6 mmol/L (100 mg/dL) optimal for most adults. For high-risk individuals, those with established heart disease, diabetes, or very high calculated cardiovascular risk, a target below 1.8 mmol/L (70 mg/dL) is recommended. Very high-risk patients may have targets below 1.4 mmol/L (55 mg/dL).
What is the Friedewald equation for LDL?
The Friedewald equation (1972) calculates LDL as: LDL = Total Cholesterol − HDL − (Triglycerides / 5) in mg/dL, or LDL = Total Cholesterol − HDL − (Triglycerides / 2.2) in mmol/L. It assumes that VLDL cholesterol equals roughly one-fifth of the triglyceride level in mg/dL, which is only valid when triglycerides are below 400 mg/dL (4.5 mmol/L). Above this level, direct LDL measurement is needed.
How do I lower my LDL cholesterol?
Dietary changes, reducing saturated fat and replacing it with unsaturated fats, increasing soluble fibre from oats, legumes, and vegetables, and adding plant sterols, can lower LDL by 10–20%. Regular aerobic exercise primarily raises HDL but can lower LDL modestly. For high-risk individuals or those with very elevated LDL, statins are the most evidence-based pharmacological intervention.