{
  "resourceType": "CodeSystem",
  "status": "draft",
  "content": "not-present",
  "name": "OnOhipDiagnosticCodesCS",
  "id": "on-ohip-diagnostic-codes",
  "title": "OHIP Diagnostic Codes (Ontario)",
  "description": "Ontario's own three-digit diagnostic code set -- the **second** code on an OHIP physician claim,\nalongside the fee code from\n[OHIP Schedule of Benefits](CodeSystem-on-ohip-schedule-of-benefits.md).\n\n**This artifact enumerates no codes.** It declares the system so that a diagnostic code pinned to it\nis recognisable as an Ontario diagnostic code and the system URI resolves to a definition. Obtain\nthe concept list from the Ontario Ministry of Health.\n\n### This set is ICD-9-LIKE, and that is the trap\n\n**Ontario's diagnostic codes share many codes with ICD-9 but the set is NOT a subset of ICD-9. Do\nnot derive one by truncating an ICD-9 code.** The range 895-971 is a parallel Ontario space laid\nover ICD-9 numbers already occupied by something unrelated:\n\n| code | means, in Ontario | means, in ICD-9 |\n|---|---|---|\n| `970` | Other Acceptable Diagnosis: Prenatal Care | poisoning by CNS stimulants |\n| `967` | Immunization: Influenza | poisoning by sedative |\n\nMeasured against the Provincial Health Care Vocabulary Standard, a SNOMED CT -> ICD-9 -> truncate\nroute reaches only **69.4%** of cases, and **124** of them land inside 895-971 and come out **valid\nand wrong** -- \"Poisoning caused by opioid receptor agonist\" becomes `970` Prenatal Care, \"Pica\"\nbecomes `307` Sleep-Wake disorders. Nothing downstream rejects those. They go on a claim, they\nadjudicate, and the diagnosis on the record is not the diagnosis the clinician made.\n\nMatching on description text instead is the same inference wearing different clothes, and it runs\nout anyway: the set has no concept for stage-3 chronic kidney disease, and the nearest neighbours\nfor Alzheimer disease and stable coronary artery disease (`290` Senile dementia, `413` angina\npectoris) each say something the chart does not.\n\nA code alone does not even determine a concept within the set: **eighteen codes carry two unrelated\nmeanings** (`072` is both \"Mumps\" and \"Gait Training\"), so the mapping is to a concept, not to a\nnumber.\n\n**Map to this set explicitly, from its own concept list. Never compute it from ICD-9.** Where no\ncorrect code exists, a wrong diagnostic code is worse than an absent one -- it adjudicates.\n\nCodes are three characters, zero-padded (for example `250`). Case-sensitive.\n\n**No canonical is published upstream.** Ontario does not publish a FHIR canonical for this set, so\nthis specification names one. The URI is stable and will not be changed.",
  "url": "https://fhir.apps.health/CodeSystem/on-ohip-diagnostic-codes",
  "experimental": false,
  "caseSensitive": true,
  "date": "2026-09-09",
  "publisher": "WELLSTAR Technologies Corp.",
  "jurisdiction": [
    {
      "coding": [
        {
          "code": "CA-ON",
          "system": "urn:iso:std:iso:3166:-2"
        }
      ]
    }
  ],
  "copyright": "The system URI is defined by this specification. The diagnostic code set itself is published by the Ontario Ministry of Health and is Crown copyright of the King's Printer for Ontario. Any codes shown on this specification's rendered page are illustrative, are NOT AN OFFICIAL VERSION, and are not maintained against the Ministry's amendment cycle; the edition in force at ontario.ca governs. This artifact itself enumerates no codes."
}