This page documents the key architectural and design decisions made in this IG, the rationale behind each decision, and the alternatives considered. Understanding these decisions helps member countries make informed choices when extending this IG nationally.

Decision 1: Frame A is Fully Mandatory

Decision: All Frame A elements — including at minimum line a (immediate cause) and the underlying cause of death — are mandatory. Lines b, c, and d are conditionally mandatory: required if the preceding line is present and the certifying practitioner identifies a further antecedent cause.

Rationale: Frame A is the clinical and statistical core of the MCCoD. A death certificate without a documented cause of death chain is not a valid MCCoD. The underlying cause of death is the primary basis for mortality statistics and must always be present. Lines b, c, and d are made conditionally mandatory rather than unconditionally mandatory because WHO guidance explicitly states they are required only "if applicable" — a single-condition death would have only line a.

Alternative considered: Making all four lines unconditionally mandatory. Rejected because it contradicts WHO MCCoD guidance and would make the IG non-conformant with real-world death certification practice across AeHIN countries.

Decision 2: Underlying Cause of Death as a Separate Mandatory Resource

Decision: The underlying cause of death is modelled as a separate mandatory MCCoDUnderlyingCauseOfDeath profile, distinct from the MCCoDCauseOfDeathCondition profiles used for lines a–d.

Rationale: WHO DORIS methodology for ICD-11 can select an underlying cause that does not appear on any line of the causal chain — for example, when a modification rule identifies a more appropriate underlying cause from the full clinical picture. If the underlying cause were always required to be one of lines a–d, DORIS-compliant implementations would be impossible to represent correctly.

openEHR alignment: The openEHR death_summary archetype has a dedicated underlying_cause_of_death data element separate from the cause_of_death cluster, confirming this as the clinically correct model.

A dorisDerived boolean extension is mandatory on MCCoDUnderlyingCauseOfDeath. When true, the code should use the ICD-11 MMS system URI, supporting audit and transparency of the coding process.

Decision 3: ICD-Version-Agnostic Cause-of-Death Coding

Decision: Cause-of-death coding uses an extensible ValueSet binding (mccod-cause-of-death-codes) that includes ICD-10, ICD-10-CM, ICD-11 MMS, and SNOMED CT system URIs. Text is always required regardless of whether a coded value is present.

Rationale: AeHIN member countries are at different stages of ICD adoption. A required binding to ICD-10 would exclude ICD-11 adopters, and vice versa. The extensible binding allows coded values from any declared system or national variant while encouraging terminology use. The mandatory text element preserves the certifying practitioner's original clinical language and supports countries without electronic coding capability.

Decision 4: Base FHIR Resources for Patient, Practitioner, and Organization

Decision: Patient, Practitioner, PractitionerRole, and Organization are referenced using base FHIR resources without any profile constraints.

Rationale: AeHIN member countries have widely varying national identifier systems, administrative structures, and existing FHIR profiles. The regional IG's role is to define the cause-of-death structure — not to prescribe how patients, practitioners, and organizations are identified nationally. Member countries that have national FHIR IGs should derive country-specific profiles from this IG that reference their national base profiles.

Decision 5: Composition as Top-Level Document Resource

Decision: The MCCoD document is represented as a FHIR Composition resource (profile: MCCoDComposition), aligned with WHO SMART Guidelines L3 conventions. The Composition is wrapped in a FHIR Bundle of type document for transport.

Rationale: Composition is the correct FHIR resource for a structured clinical document with sections, providing a natural mapping to the Frame A / Frame B structure of the WHO MCCoD form. It supports the emptyReason element for optional sections and aligns with WHO SMART Guidelines L3 document patterns.

Decision 6: Three Distinct Condition Profiles

Decision: Three separate Condition profiles are defined, each with a distinct category code from the local mccod-condition-category CodeSystem:

• MCCoDCauseOfDeathCondition — causal chain entries (lines a–d), with a mandatory linePosition extension (a/b/c/d)
• MCCoDUnderlyingCauseOfDeath — the underlying cause, with a mandatory dorisDerived extension
• MCCoDContributingCondition — Frame A Part 2 contributing conditions

Rationale: Separate profiles make the distinctions explicit, self-documenting, and unambiguous for validators and implementers. The category codes enable simple FHIR queries: Condition?category=underlying-cause-of-death retrieves the mortality coding output without ambiguity.

Decision 7: Onset-to-Death Interval as Free Text String

Decision: The "Time interval from onset to death" column (LOINC 69440-6) is captured as a free-text string extension rather than a structured FHIR Duration.

Rationale: Certifying practitioners write estimates such as "2 hours", "several weeks", or "unknown". These do not conform to the structured semantics of FHIR Duration, which requires a numeric value and a unit. A free-text string faithfully preserves the clinical record while remaining simple to implement.

Decision 8: Frame B Optional with Conditional Guidance Invariants

Decision: Frame B is entirely optional at the section level. Warning-level invariants in MCCoDComposition express conditional guidance without breaking conformance.

Rationale: Making Frame B elements mandatory would contradict the WHO MCCoD form design and would exclude lower-resource implementations. Warning-level invariants encode best-practice guidance computably — a system can be conformant without populating Frame B while still being warned when contextually appropriate data is missing. Error-level constraints are reserved for Frame A.

Decision 9: VRDR Pattern without VRDR Dependency

Decision: This IG follows modeling patterns established by the US VRDR IG but does not declare a dependency on VRDR.

Rationale: VRDR carries US-specific constraints (US Core Patient, US-specific value sets, US jurisdictional codes) that are inappropriate for AeHIN member countries. Following the VRDR pattern without inheriting the dependency gives this IG the benefit of established modeling practice while remaining genuinely regional and country-neutral.