> ## Documentation Index
> Fetch the complete documentation index at: https://docs.valiancehealth.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Procedure coding

> Code procedures to ICD-10-PCS or OPCS-4 — and understand why the procedure code decides the DRG.

Procedure coding runs through the same [`POST /api/v1/search/`](/api-reference) endpoint, with `domain: "Procedure"`.

| Vocabulary | Parameter value | Status    |
| ---------- | --------------- | --------- |
| ICD-10-PCS | `ICD10PCS`      | Available |
| OPCS-4     | `OPCS4`         | Available |

## Code a procedure

```bash theme={null}
curl https://api.v2.healthproximate.com/api/v1/search/ \
  -H "X-API-Key: hpx_..." \
  -H "Content-Type: application/json" \
  -d '{
    "query": "total knee replacement",
    "domain": "Procedure",
    "vocabulary": "ICD10PCS",
    "limit": 5
  }'
```

## Why the procedure code matters most

The DRG grouper splits surgical from medical DRGs on the **procedure** code. A case with a valid diagnosis but a missing or wrong PCS code groups MEDICAL — usually the cheaper DRG — and the revenue difference is real. If your source system records procedures in local or free-text form, code them here before you call [`POST /api/v1/drg/classify/`](/api-reference).

<Note>
  Similarity is not equivalence. A high match score on the wrong body system is still the wrong code — review procedure candidates clinically before they enter a billing path.
</Note>