# OSTA osteoporosis self-assessment

OSTA

Status: LIVE
Price: $0.005 USDC
`GET /api/calc/osta`
HTML: https://magentlab.com/docs/osta
Markdown: https://magentlab.com/docs/osta.md

Not a medical device. Not a diagnosis, dose, or listing recommendation.

## What it computes

Compute the Koh 2001 Osteoporosis Self-Assessment Tool for Asians (OSTA) as trunc(0.2 × (weight_kg − age)) toward zero, then the published low, intermediate, or high band.

## When to use

When an agent has age and weight and needs the published Koh 2001 OSTA index and band, not FRAX, not a DXA order, and not a diagnosis of osteoporosis.

## When not to use

- Not a medical device. Not a diagnosis of osteoporosis. magent does not weigh the patient.
- Not FRAX and not a DXA order. magent returns the Koh 2001 OSTA index and published band only.
- Koh 2001 derivation was postmenopausal Asian women. magent does not restrict sex or ethnicity at input.

## Formula

```
OSTA = trunc(0.2 * (weight_kg - age)); low if index > -1; intermediate if -1 to -4 inclusive; high if index < -4
```

## Citation

[A simple tool to identify Asian women at increased risk of osteoporosis](https://doi.org/10.1007/s001980170070)
Koh LKH, Sedrine WB, Torralba TP, Kung A, Fujiwara S, Chan SP, Huang QR, Rajatanavin R, Tsai KS, Park HM, Reginster JY, OSTA Research Group
Osteoporos Int. 2001;12(8):699-705
DOI: [10.1007/s001980170070](https://doi.org/10.1007/s001980170070)

## Worked example

### 66 years, 50 kg (trunc toward zero)

Given: `age=66, weight_kg=50`

1. (50 − 66) × 0.2 = −3.2
2. trunc toward zero drops decimal digits → −3 (floor would be −4)
3. index −3 is in −1 through −4 inclusive → intermediate


### 80 years, 45 kg (high)

Given: `age=80, weight_kg=45`

1. (45 − 80) × 0.2 = −7.0 → trunc −7
2. index −7 < −4 → high


### 50 years, 70 kg (low)

Given: `age=50, weight_kg=70`

1. (70 − 50) × 0.2 = 4.0 → trunc 4
2. index 4 > −1 → low


## Also searched as

- OSTA
- OST
- Osteoporosis Self-Assessment Tool
- Osteoporosis Self-Assessment Tool for Asians
- Koh OSTA
- OSTA index
- Asian osteoporosis screening
- weight minus age osteoporosis

## Parameters

- `age` (integer, required): Age in years (18-120). Koh 2001 OSTA uses age as a whole number of years.
- `weight_kg` (number, optional): Weight in kilograms. Provide weight_kg or weight_lb.
- `weight_lb` (number, optional): Weight in pounds. Converted as kg = lb * 0.45359237.

## Bulk (POST)

POST the same path with a JSON items array. The first item is the GET unit; each additional item is $0.002. Invalid items return HTTP 400 before settlement.

Method: `POST /api/calc/osta`
Max items: 25
Price: unit_amount + extra_item_amount * (n - 1) (unit 5000 atomic, extra 2000 atomic)
Status: PREVIEW

- 1 to 25 items. Each item uses the same keys as the GET query parameters.
- POST of 1 item costs the same as GET. Lists longer than 25: chunk into multiple POSTs. Extra items still execute; do not pad dummy rows.
- The first invalid item fails the whole request (index in the 400 JSON). You are not charged.
- HTTP 200 is {count, path, items}. Each items[i] is the GET 200 body for that row.
- Catalog misses (empty matches, found=false) stay paid 200s inside that slot.
- x402 resource URL is this path plus n and body_sha256. Browsers that prefer text/html get the same paywall as GET; Pay retries POST with the same items.

Example request:

```json
{
  "items": [
    {
      "age": "66",
      "weight_kg": "50"
    },
    {
      "age": "66",
      "weight_kg": "50"
    }
  ]
}
```

Human paywall (two-item fixture): https://api.magentlab.com/paywall/bulk/osta

Example 200:

```json
{
  "count": 2,
  "path": "/api/calc/osta",
  "items": [
    {
      "age": 66,
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Koh LKH, Sedrine WB, Torralba TP, Kung A, Fujiwara S, Chan SP, Huang QR, Rajatanavin R, Tsai KS, Park HM, Reginster JY, OSTA Research Group",
        "doi": "10.1007/s001980170070",
        "id": "koh-2001",
        "pmid": "11580084",
        "source": "Osteoporos Int. 2001;12(8):699-705",
        "title": "A simple tool to identify Asian women at increased risk of osteoporosis"
      },
      "formula": "osta",
      "formula_expression": "OSTA = trunc(0.2 * (weight_kg - age)); low if index > -1; intermediate if -1 to -4 inclusive; high if index < -4",
      "weight_kg": 50.0,
      "risk": "intermediate",
      "osta_index": -3
    },
    {
      "age": 66,
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Koh LKH, Sedrine WB, Torralba TP, Kung A, Fujiwara S, Chan SP, Huang QR, Rajatanavin R, Tsai KS, Park HM, Reginster JY, OSTA Research Group",
        "doi": "10.1007/s001980170070",
        "id": "koh-2001",
        "pmid": "11580084",
        "source": "Osteoporos Int. 2001;12(8):699-705",
        "title": "A simple tool to identify Asian women at increased risk of osteoporosis"
      },
      "formula": "osta",
      "formula_expression": "OSTA = trunc(0.2 * (weight_kg - age)); low if index > -1; intermediate if -1 to -4 inclusive; high if index < -4",
      "weight_kg": 50.0,
      "risk": "intermediate",
      "osta_index": -3
    }
  ]
}
```

## Response fields

- `formula` (string): osta
- `formula_expression` (string): Exact Koh 2001 expression
- `age` (integer): Age in years used in the index
- `weight_kg` (number): Normalized weight in kg
- `osta_index` (integer): Koh 2001 OSTA index: trunc(0.2 * (weight_kg - age)) toward zero. Integer; not FRAX.
- `risk` (string): low (index > -1), intermediate (index -1 through -4 inclusive), or high (index < -4). Koh 2001 published band, not a diagnosis or DXA order.
- `citation` (object): Koh 2001 Osteoporos Int citation
- `disclaimer` (string): Not-a-device notice

## Example JSON

Frozen fixture. Not a live lookup.

```json
{
  "age": 66,
  "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
  "citation": {
    "authors": "Koh LKH, Sedrine WB, Torralba TP, Kung A, Fujiwara S, Chan SP, Huang QR, Rajatanavin R, Tsai KS, Park HM, Reginster JY, OSTA Research Group",
    "doi": "10.1007/s001980170070",
    "id": "koh-2001",
    "pmid": "11580084",
    "source": "Osteoporos Int. 2001;12(8):699-705",
    "title": "A simple tool to identify Asian women at increased risk of osteoporosis"
  },
  "formula": "osta",
  "formula_expression": "OSTA = trunc(0.2 * (weight_kg - age)); low if index > -1; intermediate if -1 to -4 inclusive; high if index < -4",
  "weight_kg": 50.0,
  "risk": "intermediate",
  "osta_index": -3
}
```

## Errors

- HTTP 400 `invalid_age`: age must be an integer from 18 to 120 Returned before settlement; you are not charged.
- HTTP 400 `invalid_weight`: weight_kg (1-500) or weight_lb (2-1100) is required Returned before settlement; you are not charged.
- HTTP 400 `invalid_items`: POST body must be a JSON object with only an items array Returned before settlement; you are not charged.
- HTTP 400 `invalid_item_count`: items must be an array of 1 to 25 objects Returned before settlement; you are not charged.
- HTTP 400 `invalid_item`: each items entry must be a JSON object Returned before settlement; you are not charged.

Shared HTTP 402 and 503: https://magentlab.com/docs/payments

## Related tools

- [MUST](https://magentlab.com/docs/must) — Sum Stratton 2004 MUST (BMI, unplanned weight-loss percent, and acute disease with no nutritional intake >5 days) and return score 0–6 with risk low, medium, or high.
- [BMI](https://magentlab.com/docs/bmi) — Compute Keys/Quetelet body-mass index from height and weight, plus a WHO adult band.

## Payment

Unpaid requests return HTTP 402 even if query parameters or POST items are missing or invalid, so CDP and agents can index the path. After a PAYMENT-SIGNATURE, invalid params return HTTP 400 JSON before settlement. magent does not charge. Fix the params, then request a new 402 quote for that complete URL. Catalog misses (empty matches, found=false) are valid paid 200s.

- GET the tool with Accept: application/json (do not send Accept: text/html unless you want the human paywall).
- HTTP 402 means you have not paid. Decode the base64 PAYMENT-REQUIRED header. HTTP 503 is not a new quote.
- Sign accepts[0] (exact, EIP-3009) with validBefore = now + maxTimeoutSeconds (600 seconds), or accepts[1] (batch-settlement deposit/voucher) on product GET. Ping and POST {items} stay exact. Magent retries transient facilitator 429/5xx before answering.
- Retry the same URL with PAYMENT-SIGNATURE (base64 JSON of accepted and payload). Magent attaches canonical extensions.bazaar on CDP verify/settle; echoing 402 bazaar is optional.
- Success is HTTP 200 JSON plus PAYMENT-RESPONSE. exact settles before the tool. batch-settlement verifies (and deposit-settles) before the tool and commits the charge after HTTP 2xx. HTTP 503: retry the same PAYMENT-SIGNATURE. Mint a new exact nonce only after a new HTTP 402.

- offered `exact` on eip155:8453: Fixed-price USDC on Base. The buyer authorizes the advertised amount (EIP-3009). magent settles before the tool runs (paymentFlow upfront). extra.assetTransferMethod=eip3009 extra.paymentFlow=upfront.
- offered `batch-settlement` on eip155:8453: Payment-channel vouchers claimed later in batches. Exact stays accepts[0]. Same-path POST {items} is still exact. extra.assetTransferMethod=eip3009 extra.paymentFlow=authorization.

- not offered `upto`: Not offered. Usage-based: buyer authorizes a ceiling, seller settles the actual amount after work. Reserved for a future metered tool. Not for current calculators or code search.

Same-path POST {items} is still scheme exact: one EIP-3009 authorization for GET unit plus $0.002 per extra item. That is not x402 batch-settlement (payment channels / vouchers).

Shared HTTP 402 and 503 table: https://magentlab.com/docs/payments

Stdio MCP (one process per host): https://magentlab.com/docs/mcp

## Guarantees

- HTTP 402 is unpaid, including a missing query. After PAYMENT-SIGNATURE, invalid parameters return HTTP 400 before settlement. You are not charged. HTTP 402 never includes the tool JSON.
- exact: settlement finishes before the tool (paymentFlow upfront). batch-settlement: verify/deposit before the tool; chargedCumulativeAmount commits after HTTP 2xx. Uncertain or failed settlement fails closed (HTTP 503). Retry the same PAYMENT-SIGNATURE.
- HTTP 402 is unpaid only. Do not sign a second authorization because of a 503.
- Execution is timeout-bounded and concurrency-capped.
- Calculator inputs are stored encrypted for allowlisted operators (Magent Console). They are not in public logs, SSH lookups, catalog, or rollups. Request logs store path without query.