1 TDT4210 Lecture Sept. 14th 2005: Part 1: Coding and Classification

2 Structuring of medical data Why? –The language used in traditional patient records is redundant and not precise –Free text leads to an infinite list of possible expressions –The use of EPRs and other computer based systems has lead to a need for standardized terminlogies to represent all medically relevant expressions without any data reduction Appropriate level of detail and the structure of the classification system depend on the purpose for which the classification system has been designed

3 History of classification ICD and the classifications derived from it is the most used classification system in health care The first attempt at registration was the London Bills of Mortality in The first edition of the International List of Causes of Death, as it was then called, was presented by Jacques Bertillon at a meeting of the International Statistical Institute (ISI) in 1893 in Chicago, and it was officially accepted in This list was regularly revised under the supervision of ISI until its fifth edition in Until then, the code list was primarily used for mortality statistics. Health insurance companies, hospitals, medical services, the military, and other agencies felt a growing need to extend the list with codes for morbidity. The International Health Conference, held in New York City in 1946, entrusted the Interim Commission of the World Health Organization (WHO) with the responsibility of undertaking the necessary preparatory work to extend the International List of Causes of Death with an International List for the Causes of Morbidity.

4 Some definitions (see also Glossary) Term: Word or expression with a precise meaning, related to a particular topic Terminology: A set of terms that represents a system of concepts in a particular field Nomenclature: Codes assigned to medical concepts –Can form complex concepts by combining medical concepts –Leads to a large number of possible code combinations

5 Classifications Classifying: The process of designing a classification Classification: An ordered system of concepts within a certain domain –Examples of domains: reason for encounter (Norw.: kontaktårsak), diagnosis, medical procedure Ordering principles may be implicit or explicit Concepts ordered according to generic relations –Example: ”Pneumonia is a kind of lung disease”

6 Codes Coding is the process where a set of words describing a medical concept is translated into a code Codes may be formed by numbers, alphabetic characters, or both Different types of codes: –Number codes –Mnemonic codes –Hierarchical codes –Juxtaposition codes –Combinations

7 Requirements for a classification Domain completeness Nonoverlapping classes (mutual exclusiveness) Suitable for its purpose Homogeneous ordering (one principle per level) Clear criteria for class boundaries Unambiguous and complete guidelines for application Appropriate level of detail

8 Ordering principles Example of more than one ordering principle; classifying diseases: Anatomic location Etiology (Norw.: årsakslære) Morphology (Norw.: formlære) Dysfunction (Norw.: Funksjonsforstyrrelse) Each of these aspects can be used for different orderings called axes Multiaxial classifications use several orderings simultaneously

9 Additional requirements for computer- assisted coding systems Allow for the use of synonyms Allow for the use of lexical variations Insensitive to spelling errors Reliability –consistent operation (insensitive to ordering of terms) –correct

10 Examples of classification systems ICD – International Classification of Diseases NCSP – NOMESCO Classification of Surgical Procedures ICPC – International Classification of Primary Care SNOMED – Systematized Nomenclature of Human and Vetenary Medicine ATC – Anatomic Therapeutic Chemical Code (medications) RCC – Read Clinical Classification (Read code) MeSH – Medical Subject Headings DRG – Diagnosis Related Groups

11 ICD-9/10 (International Classification of Diseases, ) Archetypal coding system for patient record abstraction First edition published in 1900 Meant to be used for coding diagnostic terms Maintenance by WHO Most recent version: ICD-10 (1992) ICD-9 and ICD-9-CM (Clinical modifications) still much used Expanded to include other families of medical terms, e.g. reasons for encounter (”V” codes), external causes of death (”E” codes) Disease codes grouped into chapters

12 ICPC (International Classification of Primary Care) Less granularity than ICD-9 Codes for diagnoses, RfE, therapies, and laboratory tests Two-axis system: –First axis: organ systems, 17 codes (A-Z) –Second axis: components, 7 chapters, codes 1-99 Used by all GPs in Norway

13 ICPC (International Classification of Primary Care)

14 ICPC A General B Blood, blood forming D Digestive F Eye H Ear K Circulatory L Musculoskeletal N Neurological P Psychological R Respiratory S Skin T Metabolic, endocrine, nutrition U Urinary W Pregnancy, fam plan X Female genital Y Male genital Z Social

15 Extract from ICPC (Norwegian)

16 SNOMED (Systematized Nomenclature of Human and Veterinary Medicine, SNOP (Systemized Nomenclature of Pathology) Snomed (I/II) –six axes ”The Norwegian SNOMED” - Den norske SNOMED –Used in Norway today in the area of pathology SNOMED III (SNOMED International) – eleven axes SNOMED RT SNOMED CT –SNOMED RT + Clinical Terms v3 (Read Codes)

17 SNOMED (Systematized Nomenclature of Human and Veterinary Medicine, Each axis forms a complete hierarchical classification system Can combine different medical concepts to form more complex concepts using combination or juxtaposition codes Any SNOMED term may be combined with any other SNOMED term which might lead to multiple ways to express a code for the same valid concept; not always meaningful

18 SNOMED International – axes: TTopography MMorphology LLiving organisms CChemical FFunction JOccupation DDiagnosis PProcedure APhysical agents, forces, activities S Social context G General

19 SNOMED RT code structure Kilde: Coding matters, Vol. 8, No. 2, September 2001.

20 Problems/challenges Mapping between classification systems Level of details Relevant information

21 Classification problems –Not all combinations that can be generated are sensible Need both semantic and syntactic categories –Where should the disease be classified? Overlap of disease classes violates the rule of mutual exclusiveness Problems in statistical analysis –Dynamic nature of classification leads to continous need for maintenance

22 Coding problems –The language used in the classification may be very different from the clinical language used in patient records –Difficult to browse large medical classifications of diagnoses and procedures –Two different techniques used: Morpho-semantic analysis of the input languages to extract all underlying concepts, leading to a somewhat conceptual indexing of the classification Incorporation of a thesaurus with synonym expressions that all point to an existing entry in the classification

23 Literature van Bemmel & Musen: Handbook of Medical Informatics, ch. 6 KITH: ICD: ICPC: ndex.html ndex.html SNOMED: