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

# SKS procedure codes

> Filter SKS predictions to procedure codes and understand bilateral modifier expansion

SKS procedure codes span multiple groups: **K** (surgical), **UX** (examinations), **B** (treatment), **N** (anesthesia), **W** (clinical physiology), and **Z** (supplementary).

> [!TIP]
>
> See the [SKS overview](https://docs.corti.ai/coding/sks.md) for the full system description, code structure, and supported groups.

***

## Filter by procedure codes

Use the `is-a` operator with multiple ancestor prefixes to restrict predictions to procedure codes. Because SKS uses a prefix-based hierarchy, `is-a` matches each prefix and all its descendants.

**Request**: restrict predictions to SKS procedure codes (K, UX, B, Z, W, N groups) using `is-a` with multiple ancestors:

```json theme={null}
{
  "system": ["sks"],
  "context": [
    { "type": "text", "text": "Patient indlagt med akut hjerteinsufficiens og type 2-diabetes. Røntgen af højre knæ udført." }
  ],
  "filters": [
    {
      "systemId": "sks",
      "include": {
        "conditions": [
          { "property": "code", "op": "is-a", "value": ["K", "UX", "B", "Z", "W", "N"] }
        ]
      }
    }
  ]
}
```

**Response**: only procedure codes are returned:

```json theme={null}
{
  "codes": [
    {
      "system": "sks",
      "code": "UXRG25+TUL1",
      "display": "Røntgenundersøgelse af knæ, højre",
      "evidences": [
        {
          "contextIndex": 0,
          "text": "Røntgen af højre knæ",
          "start": 64,
          "end": 84
        }
      ]
    }
  ],
  "candidates": [],
  "usageInfo": {
    "creditsConsumed": 1.5
  }
}
```

> [!NOTE]
>
> The `+TUL1` suffix is a lateral modifier indicating the right side. Both diagnosis and procedure codes can carry modifiers; see [Lateral modifiers](https://docs.corti.ai/coding/sks.md#lateral-modifiers) for the full list.

[API reference →](https://docs.corti.ai/api-reference/codes/predict-codes.md)

See [code filtering](https://docs.corti.ai/coding/code-filtering.md) for full details on filter properties, operators, and additional examples.

***

## Modifiers on procedure codes

Both diagnosis and procedure codes can carry lateral modifiers (see [Lateral modifiers](https://docs.corti.ai/coding/sks.md#lateral-modifiers) for the full list). The official `proc.lateral` LPR3 code list defines which procedure codes must receive a lateral modifier; for example, `UXRG25` (Røntgenundersøgelse af knæ) is in the list. Procedure codes can also carry contrast modifiers (`UXZ11`, `UXZ12`); the `proc.kontrast` list defines which codes must receive contrast. `TUL7` (side cannot be specified) has no procedure equivalent; if the side is not documented, no laterality modifier is attached.

| Code | Display | Modifier |
| - | - | - |
| `UXRG25+TUL1` | X-ray of the knee, right | `TUL1`: right-sided |
| `UXRG25+TUL2` | X-ray of the knee, left | `TUL2`: left-sided |
| `UXRG25+TUL1+UXZ11` | X-ray of the knee, right, without contrast | `TUL1` + `UXZ11` |

> [!NOTE]
>
> `TUL3` (bilateral) is not used on procedure codes. A bilateral procedure returns two separate codes: one with `TUL1` (right) and one with `TUL2` (left). For example, a bilateral knee X-ray appears as `UXRG25+TUL1` and `UXRG25+TUL2`. Other modifiers (such as contrast) are preserved on both entries. On diagnosis codes, `TUL3` remains a single code.

## Related

* [SKS overview](https://docs.corti.ai/coding/sks.md): system description, code structure, lateral modifiers
* [SKS diagnosis codes](https://docs.corti.ai/coding/sks-diagnosis.md): filter to diagnosis codes only


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