# ApoA-I (Apolipoprotein A-I)

Apolipoprotein A-I (ApoA-I) is the main protein of 'good' HDL cholesterol. Your liver and gut make it, and it makes up about 70% of HDL's protein. It switches on an enzyme (LCAT) that drives 'reverse cholesterol transport', carrying cholesterol from your tissues back to the liver. Labs measure it by immunoassay, calibrated to a WHO/IFCC standard. Typical ranges are 110 to 180 mg/dL in men and 120 to 200 in women. It shines in one big study. In INTERHEART (12,461 cases and 14,637 controls across 52 countries), the ApoB/ApoA-I ratio was the single strongest lipid predictor of a first heart attack (odds ratio about 3.25, top vs bottom fifth). That beat the usual LDL-C/HDL-C ratio. Watch the confounders, though. Infection and inflammation drop it 20 to 30%. Pregnancy and oral estrogen raise it. Severe liver disease and rare ApoA-I mutations (Tangier disease, ApoA-I Milano) also shift it.

## Sources

- McQueen MJ, Hawken S, Wang X, et al.. (2008). Lipids, lipoproteins, and apolipoproteins as risk markers of myocardial infarction in 52 countries (the INTERHEART study): a case-control study. Lancet. https://doi.org/10.1016/S0140-6736(08)61076-4
- Walldius G, Jungner I. (2004). Apolipoprotein B and apolipoprotein A-I: risk indicators of coronary heart disease and targets for lipid-modifying therapy. Journal of Internal Medicine. https://doi.org/10.1111/j.1365-2796.2004.01345.x

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