Once the map specialist has reviewed and understands the SNOMED CT source concept to be mapped, they employ the ICD-10 Alphabetic Index to search and select candidate ICD-10 target codes for the map. They research the Fully Specified Name from the SNOMED CT source concept searching the best textual references in the Alphabetic Index that capture the meaning of the SNOMED CT concept. The WHO Alphabetic Index lists multiple term modifiers that can be considered as specifications or qualifiers of the primary term, and the map specialist will search through the specifications looking for the relevant terms of interest.

This review may identify matching ICD-10 terms or may require searching through related cross-references. Two types of cross-reference in the ICD-10 Alphabetic Index must be considered before assignment of a tentative target code(s). These are: 'See' and 'See also'.

When a code is given alongside the 'See also' instruction, as in the above example, it may or may not be necessary to look under the alternative term.

When no code is given, it is essential for the user to look under the alternative lead term.

The map specialist will create preliminary map members employing the candidate target records resulting from these searches. If specializations are noted in targets selected from the alphabetic index and there exist sub-headings for the term selected, these will be considered for exclusion rules as documented in section .

For source concepts that represent examples of poisonings caused by drugs or chemicals, the map specialist will use Section III of the Alphabetic Index, the Table of Drugs and Chemicals, to research the default maps and essential modifiers.

The map specialist will proceed from this source concept analysis to research the tabular guidance for the candidate targets and evaluate for issues of mapping context which may alter the Map members.

Release data structures for the map are compliant with SNOMED CT Release Format 2 (RF2) datasets as defined in the SNOMED CT Release File Specification. SNOMED CT release files relevant to the map structures and definitions important to map deliverables identified below include:

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Since January 2013, the SNOMED CT International Edition release package includes a mapping table from clinical concepts in SNOMED CT to codes listed in ICD-10. SNOMED CT to ICD-10 maps are represented as members of a single reference set called the ICD-10 Extended Reference Set. This reference set contains all Map member data.

Incremental changes to the ICD-10 will be documented employing the versioning mechanism supported by the standard SNOMED CT Release File Specification.

SNOMED International welcomes the opportunity to work with organizations or institutions who are interested in undertaking usage validation of the SNOMED CT to ICD-10 Map. Please contact for more information.

Rule = TruthStatement / Clause
Clause = (ClauseFinding / ClauseObservable) [ ws ANDOP ws (ClauseFinding / ClauseObservable) ] ws
TruthStatement = ws 1*1("true" / "otherwise true") ws
;;; A Rule is either a truth statement or a clause
;;; A truth statement is either "true" or "otherwise true"
;;; A clause is either a clause with a finding or a clause with an observable
;;; and value optionally followed by the AND operator and a clause with a finding or observable and value.
ClauseObservable = "IFA" ws ( AttributeObservable ws NumericOperator ws Value )
;;; Observable clause has a mandatory value
ClauseFinding = "IFA" ws ( AttributeFinding )
;;;
AttributeObservable = ConceptObservable
;;; This could be removed and AttributeObservable changed to
;;; ConceptObservable without affecting the grammar
AttributeFinding = ConceptFinding
;;; This could be removed and AttributeFinding changed to
;;; ConceptFinding without affecting the grammar
NumericOperator = ("<" / ">=")
;;;Age at onset rules use greaterthanorequals for lower bounds and lessthan for upper bound
Value = ConceptAny / Numeric / OtherText
;;; Added in ConceptAny, which allows any Concept to be used as a Value,
;;; although clearly not all concepts are suitable
ConceptObservable = SctId ws pipe ws FullySpecifiedNameObservable ws pipe
ConceptFinding = SctId ws pipe ws FullySpecifiedNameFinding ws pipe
ConceptAny = SctId ws pipe ws FullySpecifiedName ws pipe
SctId = 6*18( digit )
;;; The SctId must be a valid SNOMED CT Concept.id value
FullySpecifiedNameObservable = 1*nonwsnonpipe *( ( 1*SP "(" *SP 1*nonwsnonparennonpipe *SP ")" !( ws pipe ) ) / ( 1*SP 1*nonwsnonparennonpipe !( ws pipe ) ) ) *SP 1*1( "(observable entity)" )
;;; The FSN of an observable must have a semantic tag = "observable entity"
;;; and may contain other embedded parenthesised strings. The ! (NOT)
;;; look-ahead operator serves to prevent the parser consuming the
;;; semantic tag when it's looking for words before the tag.

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Poisonings

Source concepts representing a poisoning from a drug or noxious substance may be mapped to one, two, or three target classification codes depending upon the specificity of the source concept. The poisoning code for the drug or substance will be designated as the primary target code (mapGroup = 1), ICD-10 codes T36–T50. WHO guidance dictates that the sole exception to this rule occurs when the manifestation is a neoplastic disorder. Neoplasms are always mapped as the first target code.

Should the source concept specify the symptoms or findings resulting from the poisoning, the appropriate target code will be mapped as the second map (mapGroup = 2) except in cases of neoplastic complications when the poisoning code will occur second.

When the SNOMED CT concept specifies the action intent/site of injury involved within the event, a specific ICD classification code from range X40–X49, X60–X84, Y10–Y34, or Y40–Y59 will be employed as the second or third target code (mapGroup = 2 or 3). If the source concept does not specify intent, WHO guidance will be reviewed for a default map which will be assigned a mapCategoryId of "Properly classified" with mapAdvice of "MAPPED FOLLOWING WHO GUIDANCE".

External Causes

External causes can be found within multiple hierarchies including the event, disorder, and situation hierarchies. The corresponding maps vary according to the hierarchy in which the external causes are found and any other conditions represented within the SNOMED concept. Below are a few ways external causes may be mapped.

Source concepts which map to ICD-10 chapters with dagger and asterisk conventions will often be mapped to two target classification codes. The asterisk classification will be the second target record (mapGroup=2). The asterisk code will have applied advice of THIS CODE MAY BE USED IN THE PRIMARY POSITION WHEN THE MANIFESTATION IS THE PRIMARY FOCUS OF CARE.

Dagger codes identified during tabular review which do not have a corresponding asterisk are called "virtual dagger" references. These do not require second target addition.

There may be instances where only an asterisk is provided in a map because the dagger information is unavailable in the SNOMED CT concept. In this instance, mapAdvice THIS MAP REQUIRES A DAGGER CODE AS WELL AS AN ASTERISK CODE is appended to the map to communicate to the end user the need to add an additional corresponding code.

Exclusions

Exclusion guidelines from WHO coding publications will be evaluated as a last step in mapping context evaluation.

Review of modifiers

There are two types of modifiers which appear in the ICD-10 Alphabetical Index: essential and non-essential.

Non-essential modifiers appear in parentheses following the terms they modify and do not affect the target code selection for a given condition, sign or symptom but are considered as alternatives to the expression of the term.

The map specialist will review the ICD-10 Alphabetical Index to identify any essential modifiers which represent SNOMED CT concepts that are descendants of:

• the source concept to be mapped, or

• the source concept etiology SNOMED CT code when dagger and asterisk guidance requires a separate target for cause of the disorder. The Map Terminologist will add new Map members with the associated target specific to the alpha reference as context dependent maps with a mapRule.

Mapping for concepts of poisoning and overdose will require analysis of the Alphabetic Index's Table of Drugs and Chemicals. This table organizes drugs or chemicals along with the corresponding codes for adverse situations including accidental events, intentional self-harm, poisoning of undetermined intent, and adverse effects in therapeutic use. This table also may include essential modifiers which require attention for possible exclusion rules. For example, when mapping the SNOMED CT source concept a review of the drugs table will expose these entries for antidepressant poisoning:

In this case, the default target code for mapping of antidepressant poisoning is T43.2 for mapGroup one and X41 for mapGroup two based upon WHO advice to assume accidental poisoning when intent is unspecified. Note that essential modifiers are listed for MAO inhibitors, triazolpyridine, and tricyclic or tetracyclic antidepressants, which have potential to change the codes assigned.

The following subjections state the assumptions that are central to the construction of the ICD-10 map.

Exclusion of Implied Context

The SNOMED CT concept or statement taken from the health care record will be evaluated for meaning within the guidelines of the SNOMED CT Editorial Guide. No assumed context or modifying semantics will be inferred beyond the definition asserted by the fully specified name and the SNOMED CT defining relationships, excluding qualifiers. Identification of inconsistency between the fully specified name and the synonyms, or between the fully specified name and the defining relationships will constitute a case for ambiguity. This will cause a Map member to be flagged for editorial review by the SNOMED International terminology staff. An understanding of the meaning (semantics) of the SNOMED CT concept is a necessary first step to an understandable, reproducible, and useful map.

Reference Terminologies and Classifications

The organization, structure, and conventions of the ICD-10 classification are different than SNOMED CT. Meaning (semantics) within the classification is specified by the order and relationship of the chapters, blocks and categories. The position of a classification code within the axis, the title of the code and the associated conventions and guidance provided by the authoritative source further contribute to the specification of meaning of a classification code. Finally, since ICD-10 is an exhaustive classification, the semantic space of a particular classification code depends upon the definition of sibling codes and others within the same category. Since ICD-10 is designed for statistical and epidemiological purposes, one ICD-10 classification code may include many SNOMED CT concepts within its semantic space.

SNOMED CT is a reference terminology that expresses the semantics of concepts within its domain by means of a controlled vocabulary and use of an extensive set of defining relationships. The relationships are employed in concept definition within a constrained and defined model of meaning applicable to each SNOMED CT semantic root. Understanding the meaning of a SNOMED CT concept requires evaluation of the vocabulary term as well as the defining relationships.

The goal of the mapping process is to identify the meaning of a SNOMED CT concept, determine the best location of that concept in the ICD-10 semantic space as identified by one or more ICD-10 classification codes, and to create a link between the SNOMED CT concept identifier and the correct ICD-10 code(s). Since SNOMED CT is a reference terminology, this process cannot proceed reproducibly using only naming (terms or descriptions) conventions. A full understanding of both SNOMED CT and ICD-10 semantics is required for success.

Examples of data distributed in the ICD-10 Extended Map Reference Set are provided in an online spreadsheet accessible from the link below. These examples illustrate key points explained in various chapters of this document.

Gender

If the source concept asserts a gender restriction, a target will be selected including the restriction. If no targets with restriction apply, a more general target will be chosen. The mapCategoryId will indicate that the source is properly classified ( 447637006 | Map source concept is properly classified (foundation metadata concept)| ) in ICD-10, the mapRule will default to TRUE and mapAdvice will be NULL. The first IF A rule applied should be female; the latter should be male. This will prevent any sequencing discrepancies from resulting.

• 6738008 | Female infertility (disorder)| maps to N97.9 Female infertility, unspecified

• 2904007 | Male infertility (disorder)| maps to N46 Male infertility

If the source concept does not assert gender, yet only gender restricted target codes are found within ICD-10, the map will be considered CONTEXT DEPENDENT. The Map Terminologist will create three map members for this source concept, including rules for mapping to female and male record context as appropriate to the ICD-10 structures, and a default record indicating that the concept is not classifiable in the absence of gender information.

If the source concept asserts an age or phase of life for onset of the disorder, a target will be selected first including the restriction or, if none is available, then a more general classification target that is inclusive of the source concept. No map rule restrictions for age will be applied in cases where there is a properly classified ICD-10 target. If the authoritative sources include specifications for employment of age, those will be used. Otherwise, these definitions for common phases of life will be employed:

If the source concept does not assert age or time of life and only restricted targets are within scope, the map will be considered CONTEXT DEPENDENT and the Map Terminologist will assemble two or more Map members including Map Rules to properly classify to each ICD-10 target classification.

A source concept which identifies origination as a congenital or acquired condition will be mapped to a target of congenital or acquired classification should one exist (mapCategoryId= , mapRule=NULL).

If a source concept is general (i.e. does not specify congenital or acquired) and only specific targets exist, the ICD-10 authoritative index will be searched for a default Map member, either "congenital" or "acquired". When a default is provided, this context will be employed to create one appropriate Map member and mapCategoryId will be ( ), mapRule=NULL, mapAdvice = "MAPPED FOLLOWING WHO GUIDANCE".

Purpose

The SNOMED CT to ICD-10 map is intended to:

• leverage electronic health records, encoded using SNOMED CT, to output relevant ICD-10 codes via semi-automated clinical coding

• aid in the allocation of ICD-10 codes from SNOMED CT encoded records for use in registries and diagnosis groupers

• serve as a basis for the derivation of maps to any of the ICD-10 modifications developed and maintained by member countries

It must be understood that the map does not provide:

• a complete automation of ICD-10 clinical coding from a SNOMED CT source

• support for social, cultural, ethical or financial constraints on ICD-10 coding required by members or other organizations

• management of context beyond that found in the source terms and ICD-10 rules and conventions

Users of the map will include SNOMED International Members and Affiliates that:

• have deployed, or are deploying, SNOMED CT in clinical information systems

• use the 2016 version of ICD-10 (also known as the Fifth Edition) in systems for purposes of statistical reporting, epidemiology, cancer, injury and other registries, quality reporting, safety reporting, and research.

The map can also support use by WHO Collaborating Centers in jurisdictions where SNOMED CT is deployed or is being deployed.

The map is based on the latest monthly release of the SNOMED CT International Edition, as distributed by SNOMED International, and uses the 2016 version of ICD-10, as published and maintained by the World Health Organization, as the target classification. The map is updated for each new release of SNOMED CT.

The Map Terminologist will initiate the mapping process by evaluating the source SNOMED CT concept employing a context-free assumption: SNOMED CT concepts mapped are presumed to "speak for themselves". The concept definition as asserted in the Fully Specified Name (FSN) and the concept's defining relationships are presumed to encompass all information available for definition of the concept and interpreted as explained in the SNOMED CT Editorial Guide. This information alone will be employed by the Map Terminologist in assessing the source meaning and researching target code(s) for the Map.

If the meaning of the SNOMED CT concept is judged to be ambiguous by the Map Terminologist, the concept will be managed as follows.

Definition of ambiguity

Two cases for concern or question of ambiguity in the SNOMED CT source concept definition will include:

• Discrepancy between the FSN and associated defining relationships.

• Discordance between the SNOMED CT definition and the term descriptions/synonyms.

Discrepancies will be assessed relative to standard medical references and compared to guidance and definitions provided in the ICD-10 authoritative source. These two cases are described in more detail below:

Case #1 constitutes fundamental ambiguity in the meaning of the SNOMED CT concept and cannot be mapped pending clarification. These concepts will be assigned a Map member with mapCategoryId of . The editorial notes field will be populated with any information on the map accrued by the Map Terminologists during their research. The concept will be referred to the SNOMED CT Editors. Once the ambiguity is resolved, the map will be completed and mapCategoryId will be updated with the appropriate assignment.

Case #2 represents a confusing issue for the Map Terminologist using only lexical tools to review SNOMED CT and ICD-10. However, the SNOMED CT definition is not truly ambiguous, and the map for this concept will be completed as described herein. The SNOMED CT term which is the source of the confusion will be flagged by the Mapping Team in the notes for editorial review with the expectation that the confusing term will be marked for inactivation as a non-synonymous lexical tag.

Example of Case #2, discrepancy in synonyms:

• SNOMED CT has a synonym |Multiple duodenal erosions| and definition as a hemorrhagic inflammation of duodenal structure. The synonym implies ulceration and not hemorrhage and should likely be defined and classified as a type of duodenal ulcer.

|Hemorrhagic duodenitis (disorder)| maps to ICD-10 classification K29.8 Duodenitis. Discrepancy with concept definition will cause the map specialist to report the concept |Hemorrhagic duodenitis (disorder)| as confusing and in need of editorial review.

The context-free assumption will require agreement regarding procedures for the map when certain elements of mapping context are asserted in either the SNOMED CT source or the ICD-10 target reference. These context issues, along with mappings to multiple target codes, are detailed in the following section. In all discussions, source refers to the SNOMED CT concept and target refers to the ICD-10 classification.

Document Purpose

The ICD-10 Technical Mapping Guide outlines the intended purpose, practical use cases, and technical mapping procedures used in the development, publication, and maintenance of the SNOMED CT to ICD-10 map.

The data sets, algorithms, and intellectual products of the SNOMED CT to ICD-10 map are referred to in this document as simply ‘the map’.

Business Application

The map from SNOMED CT to the International Classification of Diseases, Tenth Revision (ICD-10) has been created to support the epidemiological, statistical, and administrative reporting needs of SNOMED International member countries and their respective WHO Collaborating Centers.

Deployment of the map supports the following business applications:

• re-use of clinical data for additional statistical purposes

• rapid submission and response to national reporting requirements

• saving time and improving efficiency for the coding professional

• improved accuracy and reproducibility of code mapping

• promulgation of widespread comparable epidemiological and statistical data

• cost savings for SNOMED International member countries which maintain ICD-10 derivative product maps

The ICD-10 map and related documentation are maintained and distributed in US English.

The map is a tabular, knowledge-based cross-link from SNOMED CT to ICD-10. It contains a set of directed relationships from a source SNOMED CT concept to one or more target ICD-10 codes that most accurately describe the meaning of the SNOMED CT concept.

ICD-10 and SNOMED CT are intended to serve different, yet complementary, purposes.

All source concepts representing neoplastic disorders will be mapped. Map Groups will specify the ICD-10 code(s) from ICD-10 Chapter II Neoplasms for the concept. Morphology mapping with ICD-O is out of scope for this map. The map advice, POSSIBLE REQUIREMENT FOR MORPHOLOGY CODE, signifies the need to add a morphology code if required by the end user.

Example

32398004 |Primary malignant neoplasm of bronchus (disorder)|

Map to C34.9 Malignant neoplasm: Bronchus or lung, unspecified , with map advice POSSIBLE REQUIREMENT FOR MORPHOLOGY CODE.

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This document describes the mapping use cases and technical procedures applied to the co-development of a SNOMED CT to ICD-10 map by SNOMED International and the World Health Organization (WHO). This document provides guidance on the intended purposes and practical use of the mapping files produced from this development.

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