Unit Converter
Cholesterol LDL – Low Density Lipoprotein
(“Bad Cholesterol” – Primary Atherogenic Lipoprotein in ASCVD)
Synonyms
- LDL cholesterol
- LDL-C
- Low-density lipoprotein cholesterol
- Beta-lipoprotein cholesterol
- “Bad cholesterol”
Units of Measurement
- mmol/L
- µmol/L
- mg/dL
- mg/100 mL
- mg%
- mg/L
- µg/mL
Description
LDL cholesterol represents the amount of cholesterol carried within LDL particles, the primary lipoproteins responsible for atherosclerotic plaque formation.
LDL-C is the most important lipid parameter for:
- Predicting ASCVD (heart attack, stroke)
- Initiating lipid-lowering therapy
- Monitoring treatment response
- Target-based lipid control
LDL particles deliver cholesterol to tissues but can infiltrate arterial walls, causing inflammation → plaque → thrombosis.
Physiological Role
LDL normally provides essential cholesterol for:
- Cell membrane synthesis
- Hormone production
- Bile acid formation
Excess LDL → oxidation → macrophage uptake → foam cell formation → atherosclerosis.
Clinical Significance
High LDL Cholesterol (Most Important)
Major Causes
- Diet high in saturated/trans fats
- Familial hypercholesterolemia (FH)
- Metabolic syndrome
- Diabetes mellitus
- Hypothyroidism
- Nephrotic syndrome
- Cholestasis
- Genetic dyslipidemias (LDL receptor, ApoB, PCSK9 defects)
Clinical importance
High LDL is strongly linked to:
- Coronary artery disease
- Stroke
- Peripheral arterial disease
LDL reduction directly reduces ASCVD events.
Low LDL Cholesterol
Usually benign.
Seen in:
- Hyperthyroidism
- Malabsorption
- Severe malnutrition
- Chronic illness
- Statin therapy
- PCSK9 inhibitor therapy
Very low LDL (<20–25 mg/dL) remains safe in studies.
Reference Intervals & Risk Categories
Normal Reference Range
- <100 mg/dL (2.6 mmol/L)
Risk-Based Classification
| LDL-C Level | Interpretation |
| < 70 mg/dL (1.8 mmol/L) | Optimal for high-risk patients |
| < 100 mg/dL (2.6 mmol/L) | Desirable |
| 130–159 mg/dL (3.4–4.1 mmol/L) | Borderline high |
| 160–189 mg/dL (4.1–4.9 mmol/L) | High |
| ≥ 190 mg/dL (≥4.9 mmol/L) | Very high (likely FH) |
Treatment Targets (Risk-Based)
- ASCVD / Diabetes / High risk: LDL < 70 mg/dL
- Very high risk: LDL < 55 mg/dL (ESC/EAS)
- Familial hypercholesterolemia: aggressive lowering required
Unit Meanings
| Unit | Meaning |
| mmol/L | millimole per liter |
| µmol/L | micromole per liter |
| mg/dL | milligram per deciliter |
| mg% | mg per 100 mL (same as mg/dL) |
| mg/L | milligram per liter |
| µg/mL | microgram per milliliter |
Diagnostic Uses
1. Cardiovascular Risk Assessment
LDL-C is the primary marker in ASCVD risk calculators.
2. Initiation of Lipid-Lowering Therapy
Guidelines use LDL-C thresholds to start:
- Statins
- Ezetimibe
- PCSK9 inhibitors
3. Monitoring Lipid Therapies
Check LDL:
- 4–12 weeks after starting therapy
- Every 3–12 months thereafter
4. Familial Hypercholesterolemia Workup
- LDL >190 mg/dL is suggestive
- Physical signs: xanthomas, corneal arcus
- Genetic testing: LDLR, ApoB, PCSK9
5. Metabolic Syndrome Evaluation
LDL often elevated with TG, low HDL.
Analytical Notes
- Fasting sample ideal if triglycerides >400 mg/dL
- Friedewald equation for LDL used when TG < 400 mg/dL:
LDL=TC−HDL−TG5\text{LDL} = \text{TC} - \text{HDL} - \frac{\text{TG}}{5}LDL=TC−HDL−5TG
- Direct LDL assays required when TG very high
- Avoid hemolysis (minimal effect)
Clinical Pearls
- LDL reduction is the most effective way to reduce heart attack & stroke risk.
- LDL >190 mg/dL always requires evaluation for familial hypercholesterolemia.
- Even normal LDL can be harmful if particle number (LDL-P) is high—seen in diabetes.
- Lifestyle + statins remain first-line therapy.
Interesting Fact
LDL particles vary in size: small, dense LDL is far more atherogenic than large, buoyant LDL-even when LDL-C levels are the same.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Lipoproteins.
- ACC/AHA 2018–2023 Cholesterol Guidelines.
- ESC/EAS Dyslipidemia Guidelines 2023.
- NCEP ATP III Lipid Classifications.
- IFCC Reference Methods for Lipid Measurement.
- Mayo Clinic Laboratories - LDL Cholesterol.
- ARUP Consult - Dyslipidemia.