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

# FHIR CodeSystem/$subsumes for concept hierarchy

> Test subsumption relationships between two OMOP concepts with FHIR $subsumes - determine parent, child, equivalent, or not-subsumed status.

## Overview

Tests whether concept A subsumes (is an ancestor of) concept B, or vice versa. Used for hierarchy-aware code validation and clinical decision support.

Supports both type-level and instance-level invocation.

## Request

```bash theme={null}
# Does "Diabetes mellitus" subsume "Type 2 diabetes mellitus"?
curl "https://fhir.omophub.com/fhir/r4/CodeSystem/\$subsumes?\
codeA=73211009&codeB=44054006&system=http://snomed.info/sct" \
  -H "Authorization: Bearer YOUR_API_KEY"
```

### By OMOP concept ID

```bash theme={null}
curl "https://fhir.omophub.com/fhir/r4/CodeSystem/\$subsumes?\
codeA=201820&codeB=201826&system=https://fhir-terminology.ohdsi.org" \
  -H "Authorization: Bearer YOUR_API_KEY"
```

### Instance-level

```bash theme={null}
curl "https://fhir.omophub.com/fhir/r4/CodeSystem/omop-v20260227/\$subsumes?\
codeA=201820&codeB=201826" \
  -H "Authorization: Bearer YOUR_API_KEY"
```

## Parameters

| Parameter | Type | Required         | Description         |
| --------- | ---- | ---------------- | ------------------- |
| `codeA`   | code | Yes              | First concept code  |
| `codeB`   | code | Yes              | Second concept code |
| `system`  | uri  | Yes (type-level) | Code system URI     |

## Response

```json theme={null}
{
  "resourceType": "Parameters",
  "parameter": [
    { "name": "outcome", "valueCode": "subsumes" }
  ]
}
```

## Possible Outcomes

| Outcome        | Meaning                                      |
| -------------- | -------------------------------------------- |
| `equivalent`   | A and B are the same concept                 |
| `subsumes`     | A is an ancestor of B (A subsumes B)         |
| `subsumed-by`  | A is a descendant of B (B subsumes A)        |
| `not-subsumed` | No hierarchical relationship between A and B |

## Examples

```bash theme={null}
# A subsumes B (Diabetes mellitus → Type 2 DM)
# → outcome: subsumes

# Reverse (Type 2 DM → Diabetes mellitus)
# → outcome: subsumed-by

# Same concept
# → outcome: equivalent

# Unrelated concepts (Type 2 DM vs Myocardial infarction)
# → outcome: not-subsumed
```

## Errors

| HTTP | Issue Code  | Cause                                           |
| ---- | ----------- | ----------------------------------------------- |
| 400  | `invalid`   | Missing `codeA`, `codeB`, or `system` parameter |
| 404  | `not-found` | Code not found in the specified code system     |