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Cholesterol HDL – High Density Lipoprotein
(“Good Cholesterol” – Cardioprotective Lipoprotein Fraction)
Synonyms
- HDL cholesterol
- HDL-C
- High-density lipoprotein cholesterol
- Alpha-lipoprotein cholesterol
- “Good cholesterol”
Units of Measurement
- mmol/L
- µmol/L
- mg/dL
- mg/100 mL
- mg%
- mg/L
- µg/mL
Description
HDL (High-Density Lipoprotein) cholesterol is the fraction of total cholesterol carried by HDL particles, which perform:
- Reverse cholesterol transport (carry cholesterol from tissues → liver)
- Anti-inflammatory effects
- Antioxidant functions
- Antithrombotic effects
- Endothelial protection
High HDL is generally cardioprotective, while low HDL is a major cardiovascular risk factor.
Physiological Role
HDL particles:
- Remove excess cholesterol from macrophages & vessel walls
- Deliver cholesterol to the liver for excretion
- Reduce atherosclerotic plaque formation
- Carry apolipoproteins (ApoA-I, ApoA-II)
- Improve endothelial NO production
- Reduce oxidation of LDL
HDL function is as important as level; however, HDL-C remains the standard clinical measure.
Clinical Significance
Low HDL Cholesterol (Most Important)
Major Causes:
- Metabolic syndrome & insulin resistance
- Type 2 diabetes
- Obesity
- Smoking
- Sedentary lifestyle
- Hypertriglyceridemia
- Beta-blockers, anabolic steroids, progestins
- Genetic disorders (ApoA-I deficiency, Tangier disease)
Clinical importance:
- Strong risk factor for atherosclerotic cardiovascular disease (ASCVD)
- Often coexists with high triglycerides + small dense LDL pattern (atherogenic dyslipidemia)
High HDL Cholesterol
Causes:
- Exercise
- Estrogen
- Moderate alcohol intake
- Genetic variants (CETP deficiency)
Clinical relevance:
Extremely high HDL (>90–100 mg/dL) may be dysfunctional and not always protective.
Reference Intervals & Risk Categories
Adult Reference Range
- Men: > 40 mg/dL (1.0 mmol/L)
- Women: > 50 mg/dL (1.3 mmol/L)
Risk Classification
| HDL-C Level | Interpretation |
| < 40 mg/dL (1.0 mmol/L) | High ASCVD risk (low HDL) |
| 40–59 mg/dL (1.0–1.5 mmol/L) | Acceptable |
| ≥ 60 mg/dL (≥ 1.55 mmol/L) | Cardioprotective |
Children
- > 45 mg/dL desirable
- < 40 mg/dL low
Unit Meanings
| Unit | Meaning |
| mmol/L | millimole per liter |
| µmol/L | micromole per liter |
| mg/dL | milligram per deciliter |
| mg% | milligram per 100 mL (same as mg/dL) |
| mg/L | milligram per liter |
| µg/mL | microgram per milliliter |
Diagnostic Uses
1. Cardiovascular Risk Stratification
Low HDL is part of:
- Metabolic syndrome
- Framingham risk score
- ASCVD pooled cohort equation
2. Monitoring Lipid Therapy
HDL changes with:
- Statins (small increase)
- Fibrates (increase HDL)
- Lifestyle therapy (exercise, weight loss)
3. Detecting Genetic Disorders
Very low HDL:
- ApoA-I deficiency
- Tangier disease
- LCAT deficiency
4. Evaluating Patients With High Triglycerides
HDL typically low in mixed dyslipidemia.
Analytical Notes
- Serum or plasma sample after 9–12 hour fast (recommended if triglycerides high)
- Direct HDL assays commonly used
- Extremely high triglycerides (>400–500 mg/dL) may interfere
- Avoid hemolysis (minimal impact but can alter turbidity)
Clinical Pearls
- HDL is inversely proportional to insulin resistance.
- Raising HDL with drugs does NOT automatically reduce ASCVD risk-focus on LDL reduction.
- HDL <40 mg/dL in men strongly predicts cardiovascular events.
- HDL can fall dramatically in:
- Acute illness
- Stress
- Infection
- Smoking
- Acute illness
Interesting Fact
HDL is called the “good cholesterol” because it literally vacuum-cleans excess cholesterol from arterial plaques and brings it back to the liver for disposal (reverse cholesterol transport).
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Lipids & Lipoproteins.
- ACC/AHA 2018–2023 Guidelines - Cholesterol Management.
- NCEP ATP III - Lipid Classification.
- IFCC Reference Method for HDL-C.
- Mayo Clinic Laboratories - HDL Cholesterol.
- ARUP Consult - Lipid Disorders.
- MedlinePlus / NIH - HDL Information.