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ApoB / ApoA1 Ratio

Compares ApoB (the protein on particles that can build up in arteries) with ApoA1 (the main HDL protein). A higher ratio is linked to more heart attacks.

AI-verified against cited sources. Awaiting expert reviewAlso called ApoB/ApoA1, ApoB/ApoA-I, ApoB:ApoA1LOINC 1874-7

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The usual range for ApoB/ApoA1 depends on sex. Choose female or male above to see where you stand.

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What it is

The ApoB/ApoA1 ratio divides your ApoB result by your ApoA1 result, both in the same unit. ApoB is the protein on the cholesterol-carrying particles that can build up in artery walls, such as LDL and VLDL. ApoA1 is the main protein on HDL, the particles that help carry cholesterol away. The ratio puts the two sides into one number. Because the units cancel, it is the same number whether the labs report mg/dL or g/L.

Why it matters

In large studies, people with a higher ApoB/ApoA1 ratio had more heart attacks. In INTERHEART, a study of heart attacks in 52 countries, the odds were about 3.3 times higher in the top fifth of the ratio than in the bottom fifth. In AMORIS, a study of more than 175,000 people, the ratio was strongly linked to deaths from heart attack in both men and women. The 2018 US cholesterol guideline summary mentions ApoB but not this ratio, so clinicians use it as extra context rather than a target.

If it’s low

A low ratio means ApoB is low compared with ApoA1, which is the favorable direction. It is common in people who are active, do not smoke and keep a healthy weight, and in people taking cholesterol-lowering treatment. It can also run in families.

Common causes

  • A healthy weight, regular activity and not smoking
  • Cholesterol-lowering treatment
  • A naturally low ApoB or high ApoA1, which can run in families
  • Pregnancy or estrogen-containing medicines, which raise ApoA1

What can help

  • A low ratio on its own does not need action
  • If ApoB is very low or you have symptoms such as greasy stools or unplanned weight loss, tell your clinician

If it’s high

A higher ratio means ApoB is high compared with ApoA1: more of the particles that can build up in artery walls, and less HDL protein. This is common, and it often goes along with higher triglycerides, extra weight or insulin resistance. Your lab marks the ratio as higher risk above about 0.9 for men and 0.8 for women (Mayo), or above 0.90 for everyone (ARUP). Your clinician can put it in the context of your overall heart risk.

Common causes

  • A diet high in saturated fat and refined carbohydrates, or weight gain
  • Insulin resistance, prediabetes or type 2 diabetes
  • High triglycerides together with low HDL cholesterol
  • Smoking
  • Low physical activity
  • Inherited conditions such as familial hypercholesterolemia or familial combined hyperlipidemia
  • An underactive thyroid or chronic kidney disease
  • Some medicines that lower ApoA1, such as androgens and progestins

What can help

  • Eat more fiber-rich foods such as vegetables, beans, oats and fruit, and fewer foods high in saturated fat
  • Aim for regular physical activity, and if you smoke, ask your clinician for help quitting
  • Ask your clinician how the ratio fits with your LDL cholesterol, non-HDL cholesterol and ApoB
  • Ask whether thyroid, kidney or blood sugar problems should be checked
  • Ask whether any of your medicines could play a role

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

The usual range depends on sex. Choose women or men to see the one that applies.

Mayo Clinic Laboratories risk categories (men, 18 and older)

  • Lower risk (under 0.7)below 0.7 ratio
  • Average risk (0.7 to 0.9)0.7 to under 0.91 ratio
  • Higher risk (above 0.9)0.91 and above ratio

Mayo Clinic Laboratories risk categories (women, 18 and older)

  • Lower risk (under 0.6)below 0.6 ratio
  • Average risk (0.6 to 0.8)0.6 to under 0.81 ratio
  • Higher risk (above 0.8)0.81 and above ratio

ARUP risk categories (adults, both sexes)

  • Low risk (0.2 to 0.6)below 0.61 ratio
  • Medium risk (0.61 to 0.90)0.61 to under 0.91 ratio
  • High risk (0.91 to 5.0)0.91 and above ratio

What can affect your result

  • Which way the lab calculates the ratio
  • Sex: Mayo uses lower cutoffs for women, ARUP uses one scale for everyone
  • Diet, weight, smoking and physical activity
  • Cholesterol-lowering treatment
  • Triglycerides, blood sugar, thyroid and kidney conditions
  • Pregnancy and estrogen-containing medicines
  • Lab method: results from different labs can differ somewhat
  • The ratio is calculated from two separate measurements, so any error in ApoB or ApoA1 carries into it.
  • Check which way the ratio runs. This catalog uses ApoB divided by ApoA1, but some labs print the inverse (ApoA1 divided by ApoB), which gives very different numbers.
  • Labs may flag very cloudy (lipemic) samples, which can disturb turbidity-based methods.
  • Different labs use different risk cutoffs, so compare a result with the range from the same lab.

When to talk to a clinician

The ratio is not an urgent test. Talk with a clinician if your result is in your lab's higher-risk category, especially with a family history of early heart disease, diabetes or other risk factors. Mention a result in the middle category at your next routine visit if you have other risk factors. If you have chest pain, trouble breathing or fainting, call 911 or your local emergency number, whatever your results are.

Questions you could ask

  • Is the ApoB/ApoA1 ratio useful for me, given my family history, triglycerides or blood sugar?
  • Which lab and unit should I stick with so my results can be compared over time?
  • How does this ratio compare with my ApoB and my LDL cholesterol?
  • Which lipid number is most useful to track for my overall heart risk?
  • Should we recheck it after a few months of lifestyle changes?
  • Is this result what you would expect given my treatment and habits?

Questions people ask

Which way is the ratio calculated?

This page uses ApoB divided by ApoA1, so a higher number is the less favorable direction. A few labs print it the other way round (ApoA1 divided by ApoB), where a higher number is more favorable. Check the label on your report before comparing results.

What ratio is considered good?

It depends on the lab. Mayo Clinic Laboratories calls under 0.7 lower risk for men and under 0.6 lower risk for women. ARUP calls 0.2 to 0.6 low risk for everyone. Both start the highest category above about 0.9 for men. Use the categories printed on your own report, and ask your clinician how they fit with your other results.

Do I need to fast for this test?

Usually not. Mayo Clinic Laboratories lists no fasting step for ApoB and ApoA1, and ApoA1 does not need fasting. Follow any fasting instructions for other tests drawn at the same time.

Show the science and sources

For clinicians and researchers

A mass ratio of apolipoprotein B to apolipoprotein A-I (LOINC 1874-7). The inverse ratio (ApoA-I/ApoB, LOINC 13462-7) exists, and some labs report it, so orientation must be checked before values are compared or trended. Mayo calculates the ratio from two turbidimetric immunoassays and ARUP from quantitative immunoturbidimetry. Mayo publishes sex-specific risk categories for adults (men: lower under 0.7, average 0.7-0.9, higher above 0.9; women: lower under 0.6, average 0.6-0.8, higher above 0.8; children 2-17: under 0.8), while ARUP publishes one scale for adults (low 0.2-0.6, medium 0.61-0.90, high 0.91-5.0). In INTERHEART (15,152 cases, 14,820 controls), the ApoB/ApoA1 ratio had the highest odds ratio (3.25 for the top versus lowest quintile) and the highest population attributable risk (49.2%) of the risk factors listed in the abstract. AMORIS (175,553 people) found that apoB and the apoB/apoA-I ratio were strongly and positively related to fatal myocardial infarction in men and women. Limits: ApoA1 is a protein mass rather than a particle count, and the ratio compounds the error of two assays.

LOINC 1874-7 (primary). Specimen: calculated.

Sources

  1. Apolipoprotein A1 and B, Serum (test APOAB), including the Apolipoprotein B/A1 ratio, Mayo Clinic Laboratories (Extended Catalog)
  2. Apolipoprotein B/A Ratio (test 0050028), ARUP Laboratories
  3. Effect of potentially modifiable risk factors associated with myocardial infarction in 52 countries (the INTERHEART study): case-control study, The Lancet (2004)
  4. High apolipoprotein B, low apolipoprotein A-I, and improvement in the prediction of fatal myocardial infarction (AMORIS study): a prospective study, The Lancet (2001)
  5. 2018 AHA/ACC/AACVPR/AAPA/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA Guideline on the Management of Blood Cholesterol: Executive Summary, Circulation (2019)
  6. Apolipoprotein A-1, Pathology Tests Explained (Royal College of Pathologists of Australasia) (2025)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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