LDL Cholesterol
LDL-C· also: LDL-C, Bad Cholesterol
Clinical Overview
LDL (low-density lipoprotein) cholesterol is the primary carrier of cholesterol in the blood and the main driver of atherosclerotic plaque formation. LDL particles infiltrate arterial walls, become oxidized, and trigger inflammation that leads to narrowing and hardening of arteries (atherosclerosis), increasing the risk of heart attack and stroke.
Why This Test Matters
LDL-C is the primary target of cardiovascular risk reduction therapy. Statins, ezetimibe, and PCSK9 inhibitors all lower LDL-C. Cardiovascular risk reduction is directly proportional to the absolute LDL-C reduction — each 39 mg/dL (1 mmol/L) reduction in LDL-C reduces major cardiovascular events by approximately 22% (CTT meta-analysis). Target LDL-C depends on risk category: <70 mg/dL for very high-risk patients, <100 mg/dL for high-risk patients.
Reference RangesWHO/IFCC standards
| Age Group | Reference Range | Unit | Notes |
|---|---|---|---|
| Adults (18–64) | 0 – 100 | mg/dL | Optimal |
| Adults (18–64) | 100 – 129 | mg/dL | Near optimal |
| Adults (18–64) | 130 – 159 | mg/dL | Borderline high |
| Adults (18–64) | 160 – 9999 | mg/dL | High |
Also reported in: mmol/L.
Critical (Panic) Values
Critical High: > 190 mg/dL. Values outside these limits require immediate clinical attention.
What Causes Abnormal Results?
High LDL-C Causes
- Familial hypercholesterolemia (FH) — genetic, LDL often >190 mg/dL
- High saturated fat and trans fat diet
- Hypothyroidism
- Diabetes and metabolic syndrome
- Nephrotic syndrome
- Anorexia nervosa
- Medications: corticosteroids, progestins, thiazides
Low LDL-C Causes
- Statin therapy (treatment target)
- Malnutrition
- Hyperthyroidism
- Liver disease
- Abetalipoproteinemia (rare genetic)
Signs & Symptoms to Watch For
How to Prepare for This Test
Fast for 9–12 hours. LDL is usually calculated using the Friedewald equation (Total-C − HDL − TG/5). Directly measured LDL is available and more accurate when triglycerides are elevated.
Factors That Can Affect Results
- Non-fasting (triglycerides rise after eating, making Friedewald calculation less accurate)
- Very high triglycerides (>400 mg/dL) — Friedewald equation invalid, direct LDL required
- Acute illness or MI (LDL drops acutely — measure within 24 hours of MI or 4–6 weeks after)
- Pregnancy (LDL rises physiologically)
Related Topics
Frequently Asked Questions
What is the target LDL for high-risk patients?
For patients at very high cardiovascular risk (known coronary artery disease, history of MI or stroke, or LDL >190 mg/dL with familial hypercholesterolemia), the ACC/AHA guidelines target LDL below 70 mg/dL. For patients at high risk (10-year ASCVD risk ≥7.5%), the target is LDL below 70–100 mg/dL. For primary prevention in lower-risk individuals, the threshold for drug treatment and optimal LDL target are individualized through a shared decision-making conversation.
Is a very low LDL safe?
Current evidence does not identify a lower limit of safety for LDL. In major trials including FOURIER (PCSK9 inhibitors) and IMPROVE-IT (ezetimibe), LDL levels below 20–30 mg/dL were achieved without adverse effects. The "lower is better" principle applies: lower LDL consistently reduces cardiovascular events with no identified threshold below which risk reduction stops.