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MasterMath

Cholesterol Ratio Calculator

The atherogenic ratios from your blood test, with LDL calculated by Friedewald when it is not measured. The ratios say more than the individual figures.

Atherogenic index (total/HDL)

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Atherogenic index (total/HDL)—
LDL/HDL—
Triglycerides/HDL—
LDL—
Non-HDL cholesterol—
Check—

How this was worked out

    Indicative result. These indices are not a cardiovascular risk estimate. That calculation uses country-specific tables including age, blood pressure, smoking and diabetes, and a doctor interprets it.

    The formula

    Castelli index I = total cholesterol ÷ HDL

    Where it comes from

    A total cholesterol of 220 does not mean the same thing with an HDL of 40 as with one of 80, which is why the ratios get used so much: they relate the cholesterol that deposits plaque to the cholesterol that removes it. Castelli index I is total over HDL, index II is LDL over HDL, and the triglyceride-to-HDL ratio tracks with insulin resistance. Non-HDL cholesterol, simply total minus HDL, groups every atherogenic particle at once.

    How to work it out by hand

    1. Take total cholesterol and HDL from the blood test
    2. If LDL is missing, work it out by Friedewald: total − HDL − triglycerides ÷ 5
    3. Divide total by HDL for the Castelli I index
    4. Divide LDL by HDL and triglycerides by HDL for the other two

    What is worth knowing

    The Friedewald formula stops working above 400 mg/dl of triglycerides, and it also underestimates LDL when LDL is low: in those cases it has to be measured directly, and you get a warning here. No ratio on its own decides anything: cardiovascular risk is worked out with tables that include age, sex, blood pressure, smoking and diabetes, and those tables depend on the country and get revised. These are the ratios from your blood test, not a risk.

    Frequently asked questions

    What Castelli index is good?

    Thresholds vary by source and by sex, which is why the number appears here without a label. Read it with your doctor and the rest of the picture.

    Why does my calculated LDL differ from the lab's?

    Because the lab may have measured it directly. Friedewald is an estimate and it fails with high triglycerides or low LDL.

    What is non-HDL cholesterol?

    Total minus HDL: every plaque-depositing particle together. It is used more and more because it does not depend on triglycerides.

    Do I need to fast?

    Not for total cholesterol and HDL. For triglycerides, and therefore for Friedewald LDL, fasting is preferable.

    Does this tell me my heart attack risk?

    No. Risk is worked out with tables that include a good many more variables and that depend on the country.