Apolipoprotein A1 (ApoA1) is the major protein component of HDL (High-Density Lipoprotein).

It plays a key role in:

• Reverse cholesterol transport

• Activation of LCAT (Lecithin–Cholesterol Acyltransferase)

• Removal of cholesterol from peripheral tissues

Normal Reference Range

• Men: 120–160 mg/dL

• Women: 140–180 mg/dL

(Values may vary by laboratory.)

Clinical Significance

1️⃣ Cardiovascular Protection

ApoA1 is considered anti-atherogenic.

Functions:

• Promotes cholesterol efflux from tissues

• Prevents LDL oxidation

• Reduces plaque formation

Low ApoA1 levels → Increased risk of:

• Coronary artery disease (CAD)

• Myocardial infarction

• Stroke

2️⃣ Better Risk Marker Than HDL-C

HDL-C measures cholesterol content in HDL.

ApoA1 reflects:

• Number of HDL particles

• Functional capacity of HDL

Therefore, ApoA1 may provide better cardiovascular risk assessment.

3️⃣ ApoB/ApoA1 Ratio

This ratio is a strong predictor of cardiovascular risk:

• High ApoB/ApoA1 ratio → High risk

• Reflects balance between atherogenic and protective lipoproteins

4️⃣ Genetic Disorders

Low ApoA1 seen in:

• Tangier disease

• Familial hypoalphalipoproteinemia

Features:

• Very low HDL

• Premature atherosclerosis

5️⃣ Liver Disease

Since ApoA1 is synthesized in the liver:

Decreased in:

• Chronic liver disease

• Cirrhosis

6️⃣ Inflammatory States

ApoA1 decreases during:

• Acute inflammation

• Sepsis

• Chronic infections

It acts as a negative acute-phase reactant.