# NIH API: Explain ICD-10-CM diagnosis code

> Explains an ICD-10-CM diagnosis code with its official name, category, chapter, and whether it is billable, using the NLM Clinical Tables diagnosis table.

Unofficial. Not affiliated with or endorsed by NIH.

- Page: https://fous.com/methods/clinicaltables.nlm.nih.gov/explain-diagnosis-code
- Method: `clinicaltables.nlm.nih.gov/explain_diagnosis_code`, version 1
- Website: clinicaltables.nlm.nih.gov
- Returns: code, official name, category code and name, chapter, billable flag, NLM page link
- Effect: read (it gets data and changes nothing)
- Sign-in: none needed
- Cost: 1 credit per completed run (1¢ with pay as you go); failed runs are free
- Verified: Nov 2, 2026

## Inputs

| Field | Type | Required | In the run below | Description |
|---|---|---|---|---|
| `code` | string | yes | `"B20"` | ICD-10-CM diagnosis code as printed, with or without the dot (for example, E11.9 or E119). |

## Output

From a run on Oct 23, 2026. Its input:

```json
{
  "code": "B20"
}
```

Its output:

```json
{
  "code": "B20",
  "chapter": "Certain infectious and parasitic diseases",
  "billable": true,
  "page_url": "https://clinicaltables.nlm.nih.gov/api/icd10cm/v3/search?terms=B20&sf=code",
  "category_code": "B20",
  "category_name": "Human immunodeficiency virus [HIV] disease",
  "official_name": "Human immunodeficiency virus [HIV] disease"
}
```

## Run it

From code, with a Fous API key in `FOUS_API_KEY`; the answer's `data` holds the output:

```bash
curl https://api.fous.com/v1/runs \
  -H "Authorization: Bearer $FOUS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"method":"clinicaltables.nlm.nih.gov/explain_diagnosis_code","input":{"code":"B20"}}'
```

From an AI agent connected to the Fous MCP server: its `run` with the same method and input. To connect one, give it `set up https://fous.com/SKILL.md`.

## Ask your agent

- What does ICD-10-CM code E11.9 mean, and is it billable?
- Look up the official name and chapter for diagnosis code J45909.
- Can you explain the ICD-10-CM code I10 and which category it belongs to?
- I need the billing status and full description for code M54.5 on nih.gov.
- Which chapter does ICD-10-CM code S72001A fall under, and what is its official name?

## Input schema

```json
{
  "type": "object",
  "required": [
    "code"
  ],
  "properties": {
    "code": {
      "type": "string",
      "description": "ICD-10-CM diagnosis code as printed, with or without the dot (for example, E11.9 or E119)."
    }
  }
}
```

## Output schema

```json
{
  "type": "object",
  "required": [
    "code",
    "official_name",
    "category_code",
    "category_name",
    "chapter",
    "billable",
    "page_url"
  ],
  "properties": {
    "code": {
      "type": "string",
      "description": "Diagnosis code with a dot after the first three characters."
    },
    "chapter": {
      "type": "string",
      "description": "ICD-10-CM chapter name in words."
    },
    "billable": {
      "type": "boolean",
      "description": "Whether the code is sufficiently specific to bill."
    },
    "page_url": {
      "type": "string",
      "description": "Link to the code in the NLM Clinical Tables search."
    },
    "category_code": {
      "type": "string",
      "description": "Three-character ICD-10-CM category code."
    },
    "category_name": {
      "type": "string",
      "description": "Official three-character category name."
    },
    "official_name": {
      "type": "string",
      "description": "Official diagnosis name."
    }
  }
}
```

## See more

- [NIH API: Search diagnosis codes](https://fous.com/methods/clinicaltables.nlm.nih.gov/search-diagnosis-codes.md): Finds ICD-10-CM diagnosis codes and official names from a plain-language condition description, retrying with simplified wording when the first search finds nothing.
- [NIH API: Search grants](https://fous.com/methods/reporter.nih.gov/search-grants.md): Finds NIH research grants by topic, organisation, or researcher name. Searches the last five fiscal years by default.
- [NIH API: Search PubMed articles](https://fous.com/methods/pubmed.ncbi.nlm.nih.gov/search-articles.md): Finds PubMed medical and life-science articles by topic, with publication details and free full-text links when PubMed confirms them.
- [NIH API: Get chemical facts by name or CAS number](https://fous.com/methods/pubchem.ncbi.nlm.nih.gov/get-chemical.md): Looks up a chemical on PubChem by common name or CAS number and returns its formula, molecular weight, names, description, SMILES, InChIKey and 2D structure image link.
- [NIH API: Get PubMed article](https://fous.com/methods/pubmed.ncbi.nlm.nih.gov/get-article.md): Gets the full PubMed abstract and publication details for one article by title, PubMed link, or PubMed number (PMID). A title is searched in PubMed titles first and must closely match a found article. Some articles have no abstract or free full text.
- [NIH API: Get chemical safety](https://fous.com/methods/pubchem.ncbi.nlm.nih.gov/get-chemical-safety.md): Looks up a chemical on PubChem by name or CAS number and returns its GHS hazard labels, route-specific first aid, flash point and workplace exposure limits.
- [MedlinePlus API: Explain a lab test](https://fous.com/methods/medlineplus.gov/explain-lab-test.md): Explains a MedlinePlus medical test: what it measures, why it is ordered, how it is done, preparation, risks, and what the results mean.
- [MedlinePlus API: Get health topic](https://fous.com/methods/medlineplus.gov/get-health-topic.md): Looks up a MedlinePlus health topic for a condition or symptom and returns its overview, related topics, and encyclopedia sections when a matching article is linked.
- [All NIH methods](https://fous.com/methods/nih.gov.md)