HDL Cholesterol

← Back to Lab Reference Library

Category: Inflammation and Cardiovascular  |  Also known as: HDL-C, High-Density Lipoprotein Cholesterol, "Good Cholesterol"  |  Sample: Serum (12-hour fast required)

1. What This Test Measures

HDL cholesterol (HDL-C) measures the cholesterol content carried within high-density lipoprotein particles. HDL particles are the smallest and densest of the lipoproteins, composed of a phospholipid shell surrounding a core of cholesterol esters and triglycerides, studded with apolipoprotein A-I (apoA-I) as the primary structural and functional protein. The "good cholesterol" label, while directionally correct, dramatically oversimplifies what HDL actually does.

HDL performs at least three critical cardiovascular protective functions. Reverse cholesterol transport (RCT): HDL particles remove cholesterol from peripheral tissues, including cholesterol-laden macrophages (foam cells) in arterial walls, and transport it back to the liver for excretion into bile. This is the mechanism by which HDL directly reduces atherosclerotic plaque burden. Anti-inflammatory function: HDL carries the enzyme paraoxonase-1 (PON-1), which hydrolyzes oxidized lipids in LDL particles and arterial walls, reducing the inflammatory stimulus that drives plaque progression. HDL also carries sphingosine-1-phosphate (S1P), which promotes endothelial barrier function and suppresses vascular inflammation. Antioxidant protection: HDL prevents LDL oxidation by accepting oxidized phospholipids from LDL particles, converting atherogenic oxidized LDL back to a less harmful form.

The standard lipid panel measures HDL-C, the cholesterol content of HDL particles, not the number of HDL particles (HDL-P) or their functional capacity. This distinction matters clinically: two patients with identical HDL-C of 55 mg/dL may have very different numbers of HDL particles and very different reverse cholesterol transport capacity. In the setting of chronic inflammation, HDL particles can become dysfunctional, losing their anti-inflammatory and RCT capacity and becoming pro-inflammatory despite a "normal" HDL-C number on the lab report.

2. Why This Test Matters

• Cardiovascular risk assessment: low HDL is an independent cardiovascular risk factor. HDL below 40 mg/dL (men) or below 50 mg/dL (women) significantly increases cardiovascular event risk regardless of LDL levels. HDL above 60 mg/dL is considered a negative (protective) risk factor by NCEP ATP III guidelines
• Insulin resistance marker: the combination of low HDL and elevated triglycerides is the lipid signature of insulin resistance. This pattern (sometimes called atherogenic dyslipidemia) is often the earliest lipid abnormality in the metabolic syndrome progression
• TG/HDL ratio: the triglyceride-to-HDL ratio is the most accessible proxy for LDL particle size and insulin resistance. Low HDL drives the ratio higher, compounding the risk signal from elevated triglycerides
• Metabolic syndrome criterion: HDL below 40 mg/dL (men) or below 50 mg/dL (women) is one of the five diagnostic criteria for metabolic syndrome
• Statin therapy context: statins reduce LDL but do not significantly raise HDL. A patient on a statin with a low HDL still has significant residual cardiovascular risk that the statin is not addressing. This residual risk is often the difference between adequate and comprehensive cardiovascular risk management
• Dietary pattern indicator: HDL responds to dietary composition. Low-fat, high-carbohydrate diets reduce HDL and raise triglycerides. Moderate-fat diets rich in monounsaturated fats (Mediterranean pattern) raise HDL and improve the TG/HDL ratio

3. Standard Lab Reference Range

HDL Level	Conventional Classification	Clinical Notes
Below 40 (M) / 50 (F)	Low (cardiovascular risk)	Independent risk factor; one of five metabolic syndrome criteria
40 to 59 mg/dL	Normal	Acceptable range; functional medicine targets above 60
60 mg/dL or above	High (protective)	Negative risk factor by ATP III; offsets one positive risk factor
Above 90 to 100 mg/dL	Very high	Not always additionally protective; evaluate for dysfunctional HDL in context of elevated hs-CRP

4. Optimal Functional Medicine Range

HDL Level	Functional Interpretation
Below 40 mg/dL	Critically low: significant cardiovascular and metabolic risk requiring active intervention
40 to 49 mg/dL	Suboptimal: insulin resistance likely contributing; dietary and exercise optimization indicated
50 to 59 mg/dL	Acceptable: approaching optimal; continue lifestyle optimization
60 to 80 mg/dL	Optimal: cardioprotective range; strong RCT and anti-inflammatory function expected
Above 80 mg/dL	Excellent: typically seen with consistent exercise, healthy dietary fat intake, and good insulin sensitivity

5. HDL in the Complete Lipid and Metabolic Panel

Marker	What It Adds	FM Optimal
HDL-C (this page)	Reverse cholesterol transport capacity; anti-inflammatory function	Above 60 mg/dL
TG/HDL Ratio	LDL particle size proxy; insulin resistance index	Below 2.0
Triglycerides	Hepatic lipogenesis; inversely correlates with HDL	Below 80 mg/dL
Oxidized LDL	Atherogenic LDL; HDL prevents LDL oxidation	Below 60 U/L
hs-CRP	Inflammation status; chronic inflammation makes HDL dysfunctional	Below 1.0 mg/L
Fasting Insulin	Insulin resistance; primary driver of low HDL and elevated TG	2 to 6 uIU/mL

6. Symptoms Associated With Low HDL

7. What Causes Low HDL

• Insulin resistance: the most common modifiable cause of low HDL. Hyperinsulinemia increases hepatic lipase activity, which degrades HDL particles faster than they can be produced. Simultaneously, elevated triglycerides (driven by insulin resistance) exchange triglycerides into HDL particles through CETP, making HDL triglyceride-enriched and susceptible to hepatic lipase degradation
• Sedentary lifestyle: physical inactivity is the second most impactful modifiable driver of low HDL. Exercise increases HDL by stimulating apoA-I production, reducing hepatic lipase activity, and improving the maturation of nascent HDL particles into cholesterol-rich, functional HDL
• Smoking: reduces HDL by 5 to 10 mg/dL through direct endothelial damage, increased oxidative stress, and reduced apoA-I production. Smoking cessation raises HDL measurably within 3 to 6 months
• High-carbohydrate, low-fat diets: excess refined carbohydrates drive triglyceride production and reduce HDL through the CETP-mediated exchange mechanism. This is why low-fat diets often worsen the very lipid pattern (high TG, low HDL) they are intended to improve
• Obesity: visceral adipose tissue drives insulin resistance and the entire metabolic dyslipidemia cascade. Visceral fat reduction is one of the most effective interventions for raising HDL
• Medications: beta-blockers (reduce HDL by 5 to 10%), anabolic steroids, progestins, and thiazide diuretics can lower HDL
• Hypothyroidism: thyroid hormones regulate hepatic apoA-I production and lipid metabolism. Subclinical and overt hypothyroidism reduce HDL and should be evaluated in any patient with unexplained dyslipidemia
• Genetics: familial hypoalphalipoproteinemia and Tangier disease are rare genetic causes of very low HDL. More commonly, genetic variation in CETP, hepatic lipase, and ABCA1 produces moderate HDL variation between individuals

8. How to Raise HDL

9. Related Lab Tests

10. When Testing Is Recommended

• Standard lipid panel component for all adults over 20 (functional medicine recommends annual testing)
• Any patient with metabolic syndrome risk factors: abdominal obesity, elevated triglycerides, elevated blood pressure, elevated fasting glucose
• Patients on statin therapy: HDL identifies residual cardiovascular risk that statins do not address
• Family history of premature cardiovascular disease (men under 55, women under 65)
• Monitoring response to dietary and lifestyle intervention: HDL responds to exercise and dietary changes within 4 to 8 weeks
• Patients with insulin resistance or type 2 diabetes: low HDL/high TG is the characteristic dyslipidemia
• Comprehensive cardiovascular assessment alongside TG/HDL ratio, oxidized LDL, Lp-PLA2, and hs-CRP
• Evaluate alongside inflammatory markers to assess HDL functionality, not just quantity

11. Clinical Perspective

12. Frequently Asked Questions