OSTA: A Two-Number Guide to Whether You Need a Bone Density Scan

• What OSTA is and where it came from
• How to calculate your own OSTA score from age and weight
• How the result relates to the decision to have a bone density (DXA) scan
• The difference between OSTA and FRAX -- the "two numbers" and what each one is for

OSTA (Osteoporosis Self-Assessment Tool for Asians) is a screening index developed for Asian populations. It was published in 2001 from data on postmenopausal women in eight Asian countries -- Singapore, Taiwan, Korea, Hong Kong, Malaysia, the Philippines, Thailand and China -- and was validated in Japanese women.

It was designed for a practical problem: in places where bone density scanners are scarce, who should be scanned first? The researchers collected many risk factors, and found that age and body weight alone identified most women likely to have osteoporosis.

OSTA does not tell you "you have osteoporosis." It tells you whether a bone density scan is probably worth having.

In Japan, a draft national osteoporosis screening manual prepared by a Ministry of Health, Labour and Welfare research group now places OSTA, alongside FRAX risk factors, at the centre of community screening. This approach may be adopted by municipal screening programmes in the coming years.

The formula is short:

OSTA = (weight in kg − age in years) × 0.2, rounded toward zero to a whole number.

An even simpler check that means almost the same thing: is "age minus weight" 5 or more?

Enter your age and weight in the calculator below to see your score.

Worked examples

• Age 70, 45 kg → (45 − 70) × 0.2 = −5 → high risk
• Age 62, 52 kg → (52 − 62) × 0.2 = −2.0 → −2 → intermediate risk
• Age 55, 60 kg → (60 − 55) × 0.2 = +1 → low risk

Use your current weight, not the weight you remember from years ago. The figure on your last health check is fine.

If your score is in the low-risk range (greater than −1)

Osteoporosis is relatively unlikely. But OSTA looks at only two things. If any of the following apply to you, talk to your doctor regardless of the score:

• You have broken a bone from a minor fall or bump as an adult
• You have taken oral steroid medication for a long period
• Your periods stopped before age 45
• You have a condition that affects bone, such as rheumatoid arthritis or diabetes

If your score is in the intermediate range (−1 to −4)

This is a "consider a scan" result. It does not mean anything is about to happen. At your next appointment, you could simply say: "My OSTA score was in the intermediate range. Should I have a bone density scan?"

If your score is in the high-risk range (less than −4)

A bone density scan is recommended. The number may feel alarming, but it is best read as a prompt: now is a good time to find out how your bones are doing. Osteoporosis, once found, is a condition that can be managed.

The older you are, the more likely OSTA is to say "get a scan." Most people in their 70s and 80s fall into the intermediate or high-risk range. That is not a quirk of the arithmetic -- it reflects the fact that a bone density scan is recommended at that age anyway. If you have never had one, let this be the nudge.

If you have had a fragility fracture, the score doesn't matter

If you have broken a bone from a minor impact as an adult, a bone density scan is recommended whatever your OSTA score. A prior fracture carries more weight than age or body weight.

Many things influence osteoporosis risk: family history, age at menopause, smoking, alcohol, exercise, calcium intake, and more. In the study that created OSTA, eleven factors were initially linked to osteoporosis.

When the weaker factors were removed one by one, age and weight on their own performed almost as well as the full list.

• Age: after menopause, bone density declines steadily with each decade
• Weight: lighter people load their bones less and tend to have lower bone mass

Because "older and lighter" is such a strong signal, two numbers are enough for a useful first screen.

This does not mean that being heavier is protective. What matters for bone is maintaining a healthy weight and keeping your muscle -- gaining weight is not a bone-health strategy.

This site also covers FRAX. The two tools look similar but answer different questions.

Put simply: OSTA is the front-door question -- should I get scanned? -- and FRAX is the follow-up -- given everything, including my scan, what next?

How the two are combined in the proposed Japanese screening flow

The draft screening manual proposes combining them like this:

1. Ask about prior fragility fracture first -- if yes, refer for a DXA scan
2. Calculate OSTA -- a score of −1 or below (age − weight ≥ 5) counts as "OSTA positive"
3. Check the FRAX risk-factor questions (parental hip fracture, current smoking, steroids, rheumatoid arthritis, secondary osteoporosis, alcohol) -- any one counts as "FRAX positive"
4. Decide by age:
   • Age 40–64: positive on both → refer for DXA; positive on one → health guidance (DXA on request)
   • Age 65 and over: positive on either → refer for DXA

This is still a draft, and municipal programmes will not change overnight. But the underlying idea -- that everyday information alone can identify who most needs a scan -- is useful when you are weighing the decision for yourself.

What it can tell you

• Whether a bone density scan is probably worth having
• The most basic osteoporosis risk pattern: being older and lighter

What it cannot tell you

• Your actual bone density: OSTA is not a substitute for a DXA scan
• Your fracture probability: that is what FRAX is for
• Bone quality or fall risk: bone microstructure, muscle strength and balance are not part of OSTA
• Risks other than age and weight: prior fracture, steroid use and early menopause are not captured, so tell your doctor about them separately

OSTA was developed from data on postmenopausal women. It is sometimes applied to premenopausal women and to men, but it has been tested less thoroughly in those groups. Men should treat the result as a reason to raise the topic with their doctor, not as a verdict.

• "I calculated something called OSTA from my age and weight and came out in the intermediate (or high) range. Should I have a bone density scan?"
• "Can I have a DXA scan here? Is it covered by insurance?"
• "Am I eligible for the municipal osteoporosis screening programme?"
• "I broke a bone some years ago -- does that affect what my bone density means?"

• Do the sum. Use the calculator above, or work it out: if your age minus your weight is 5 or more, it is time to think about a scan.
• If you are in the intermediate or high range, say one sentence at your next appointment. "I'd like a bone density scan" is enough.
• Look at FRAX too. If OSTA points you toward a scan, reading through the seven FRAX questions will make the conversation with your doctor smoother.
• Read up on the DXA scan so you know what to expect and how to read the result.

Q. Does OSTA work for men?

OSTA was built from data on postmenopausal women, but studies in Asian men have found that the same age-and-weight index is a usable screen. The evidence is thinner than for women, so men should treat the result as a prompt to discuss a scan rather than a conclusion. See also our article on osteoporosis in men.

Q. Can I use it if I am under 40?

You can do the arithmetic, but OSTA was designed for postmenopausal women. If you are younger and concerned about your bones (early menopause, long-term steroid use, very low body weight), talk to your doctor rather than relying on the score.

Q. If I gain weight, will my risk go down?

Being underweight is a risk factor, but gaining weight is not a way to protect your bones. What matters is keeping a healthy weight and preserving muscle. See nutrition for strong bones and exercise and fall prevention.

Q. I've already had a bone density scan. Do I need OSTA?

No. OSTA only helps decide whether to have a scan. If you already have a result, that result is what counts. Our DXA guide explains how to read it.

Q. If I'm low risk, can I skip the scan?

Low risk means "a scan is probably not urgent," not "you don't need one." Anyone with a prior fracture or steroid use should still be assessed, and most guidelines suggest that postmenopausal women have their bone density measured at least once. If in doubt, ask your doctor.

Q. How is OSTA different from your risk checklist?

Our risk checklist is a broad review of the factors linked to osteoporosis. OSTA takes just two of them -- age and weight -- and turns them into a number that guides the scan decision. If many items on the checklist applied to you, talk to your doctor whatever your OSTA score.

• FRAX: Calculating Your 10-Year Fracture Risk -- OSTA's partner tool
• The Bone Density Scan (DXA) -- for those OSTA points toward a scan
• Who Is at Risk of Osteoporosis -- the risk factors beyond age and weight
• Osteoporosis in Men

• Koh LK, Sedrine WB, Torralba TP, Kung A, Fujiwara S, et al. A simple tool to identify Asian women at increased risk of osteoporosis. Osteoporos Int. 2001;12(8):699-705. PMID 11580084 (original OSTA paper; 860 women from eight Asian countries; at a cutoff of −1, sensitivity 91%, specificity 45%, AUC 0.79; in a Japanese validation sample, sensitivity 98%, specificity 29%)
• Fujiwara S, Masunari N, Suzuki G, et al. Performance of osteoporosis risk indices in a Japanese population. Curr Ther Res. 2001;62(8):586-593. (1,123 postmenopausal Japanese women; sensitivity 88%, specificity 43% against lumbar-spine BMD below 70% of the young adult mean)
• Horii C, Tanaka S, Iidaka T, Fujiwara S, Iki M, et al. Towards efficient osteoporosis screening: a simple and practical approach using OSTA and FRAX risk factors. J Bone Miner Metab. 2026;44(4):521-529. PMID 42071064 (1,060 Japanese women aged 40–74 from the ROAD cohort; for detecting low bone mass, OSTA ≤ −1 gave sensitivity 83.7%, specificity 62.6%, AUC 0.81; "OSTA ≤ −1 or any FRAX risk factor" gave sensitivity 90.4%, specificity 47.2%)
• Chandran M, Wong CMJ, Helgason B, et al. Revisiting the Osteoporosis Self-Assessment Tool (OST): evidence from a multi-cohort study in Asia supporting age-dependent thresholds. Osteoporos Int. 2026. PMID 42360325 (2,787 women and 1,465 men; fixed cutoffs perform very differently across age groups)
• Kung AW, Ho AY, Ross PD, Reginster JY. Development of a clinical assessment tool in identifying Asian men with low bone mineral density and comparison of its usefulness to quantitative bone ultrasound. Osteoporos Int. 2005;16(7):849-855. (420 Chinese men aged 50 and over; at a cutoff of −1, sensitivity 82%, specificity 67%)
• Ministry of Health, Labour and Welfare (Japan) Health Sciences Research Grant. Draft manual for osteoporosis screening and health guidance (新骨粗鬆症検診・保健指導マニュアル案), chapters on OSTA (Fujiwara S) and screening criteria (Yoshimura N, Tanaka S). 2024. https://mhlw-grants.niph.go.jp/system/files/report_pdf/202408033A-sonota.pdf
• Japan Osteoporosis Society, Japanese Society for Bone and Mineral Research, Japan Osteoporosis Foundation (eds). Guidelines for the Prevention and Treatment of Osteoporosis, 2025 edition. Life Science Publishing.

This article provides general medical information and does not recommend any specific diagnosis or treatment. An OSTA score is a guide to whether a bone density scan is worth having; it is not a diagnosis. Bone status is determined by a DXA scan, and treatment decisions are made by your doctor. If anything here concerns you, please discuss it with your doctor.