1. Coding and Classification
Lection 2
Associated professor Andriy Semenets
Department of Medical Informatics I.Ya.Horbachevsky Ternopil State Medical University

2. Basic Questions Introduction to classification Classification basics
Medical Classification Systems

3. Important References
HANDBOOK of MEDICAL INFORMATICS. (Editors: J.H. van Bemmel, Erasmus University, Rotterdam) :
Book:Handbook of Biomedical Informatics

4. 1. Introduction to classification
In the traditional patient record, data are available in written format only, mainly as free text, but sometimes also as numeric data, such as laboratory test results.
Reconstructing the patient history from such a handwritten patient record by a clinician other than the original author is hindered by the fact that many medical terms are ill-defined and are perhaps even ambiguous.

5. 1. Introduction to classification
Medical coding is the process of assigning standardized medical codes (numerical, mnemonic, etc.) to patient medical charts. This coded information is used to:
ensure of the insurance companies;
government organizations (Medicare, USA);
patients alike all receive accurate billing statements for medical services performed.

6. 1. Introduction to classification

7. 1. Introduction to classification

8. 1. Introduction to classification
Advantages of coding medical data:
Data reduction
Standardized terminology
Enabling statistical overviews and research
Support of management and planning
Coupling with decision-support systems

9. 2. Classification basics
Classification definftion
Purpose and concepts
Ordering Principles
Nomenclatures and Thesauri
Codes
Taxonomy
Nosology

10. 2.1. Classification definition
The term classifying has two different meanings:
the process of designing a classification;
the coding or description of an object by using codes or terms that are designators of the concepts in a classification.

11. 2.1. Classification definition
We will use only the first meaning of classifying:
A classification is an ordered system of concepts within a domain, with implicit or explicit ordering principles.
A classification is based on prior knowledge and forms a key to the extension of knowledge

12. 2.2. Purpose and concepts The purpose of a classification is:
(example) to support the generation of health care statistics or to facilitate research.
Examples are the classification of abnormalities of electrocardiograms or diagnoses of patients into disease classes.

13. 2.2. Purpose and concepts

14. 2.2. Purpose and concepts
Concepts are ordered according to generic relations.
Generic relations are relations of the type "A is a kind of B," (for example, pneumonia is a kind of lung disease, where pneumonia represents the narrower concept and lung disease represents the broader concept).

15. 2.2. Purpose and concepts
Classifications contain concepts within a certain domain.
The domain can be defined as:
The set of elements to which a variable or function is limited.
Any area of interest that might be modeled, e.g., to create an information system.

16. 2.2. Purpose and concepts
Examples of domains are reason for encounter, diagnosis, and medical procedure.
In this respect the International Classification of Diseases, 9th edition (ICD-9), is a classification of diagnoses.
A classification allows one to compare findings collected in different environments.
Classifying is done according to a single criterion: age; that is, age is used as a differentiating criterion

17. 2.3. Ordering Principles
In classifying diseases we deal with the following aspects, among others:
anatomic location,
etiology,
morphology, and
dysfunction.
Each of these aspects can be used for a different ordering. Such an ordering throughout a classification is called an axis.

18. 2.3. Ordering Principles
Multiaxial classifications use several orderings simultaneously.
In the International Classification of Primary Care (ICPC), for instance, the diagnoses are classified along two axes, one for the organ system (an alphabetic character) and one for the components.
ICPC has primarily been designed for epidemiological purposes.

19. 2.3. Ordering Principles
One of the problems of uniform registration in health care is the lack of a common terminology
A thesaurus is a list of terms used for a certain application area or domain. Examples are a list of diagnostic terms or a list of terms for laboratory tests.
For practical usage, thesauri that also contain a list of synonyms for each preferred term have also been developed.

20. 2.3. Ordering Principles
A restricted set of preferred terms used within an organization for a given purpose is called a controlled vocabulary.
In a nomenclature, codes are assigned to medical concepts, and medical concepts can be combined according to specific rules to form more complex concepts. This leads to a large number of possible code combinations.

21. 2.3. Ordering Principles
The difference between a classification system and a nomenclature is that in the former possible codes are predefined, whereas in the latter a user is free to combine codes for all aspects involved.
The retrieval of records for patients whose data fulfill certain classification codes from a large database is relatively easy; retrieving records for patients stored by using a nomenclature is more difficult because of the high degree of freedom, leading to very complex codes.

22. 2.3. Ordering Principles
Example of a multilevel classification of medical procedures. The differentiating criteria are indicated between rectangles. The criteria for membership in each subclass are not adopted here.

23. 2.3. Ordering Principles: Summary
Terminology
Thesaurus
Classification
Vocabulary
Nomenclature
Coding System
 list of terms
 ordered terms/synonyms
 member_of arrangement
 definitions
 composition rules
 codes as designators

24. 2.3. Examples
In 1933, the New York Academy of Medicine started work on a database of medical terms, the Standard Classified Nomenclature of Diseases.
The American Medical Association continued this work in 1961, and in 1965 the Systematic Nomenclature of Pathology (SNOP) coding system was published by the American College of Pathologists.
SNOP formed the basis for the development of the Systematized Nomenclature of Human and Veterinary Medicine ( SNOMED), which is an example of such a nomenclature.

25. 2.3. Examples
SNOMED-CT: Terminology, Thesaurus, Classification, Vocabulary, Nomenclature, Coding System
ICD-10: Terminology, (Thesaurus), Classification, Vocabulary, Nomenclature, Coding System

26. 2.4. The Codes
Terminology for coding means that three basic elements are used in the so-called semantic triangle: (1) object, (2) concept, and (3) term.
Objects, also called referents, are particular things in reality, and they are concrete (e.g., the stomach), as well as abstract (e.g., the mind).
A concept is a unit of thought formed by using the common properties of a set of objects (e.g., an organ).
A term is a designation by a linguistic expression of a concept or an object in a specific language.

27. 2.4. The Codes

28. 2.4. The Codes
Coding is the process of assigning an individual object or case to a class, or to a set of classes in the case of a multiaxial classification.
In most classifications, classes are designated by codes.
Coding is, in fact, interpretation of the aspects of an object.
Example: coding gender Male = m Female = f

29. 2.4. The Codes Different types of codes included:
Number codes may be issued sequentially. This means that each new class will be given the next unused number. The advantage is that new classes can easily be added.
Numbers could be issued at random to avoid any patient-specific information is hidden in the code.
Series of numbers can be reserved for sets of classes. Issuing this type of number is only of use with a fixed set of classes, that is, when no expansion of the set of classes is expected.

30. 2.4. The Codes
A mnemonic code is formed from one or more characters of its related class rubric.
Advantages: this helps users to memorize codes.
Disadvantages: for classifications with many classes this may lead either to long codes or codes with no resemblance to the class rubrics.
Used for limited lists of classes.
Example - hospital departments are often indicated by a mnemonic code: ENT - Department of Ear, Nose, Throat, CAR - Cardiology, OB-GYN - Department of Obstetrics and Gynecology.

31. 2.4. The Codes
Hierarchical codes are formed by extending an existing code with one or more additional characters for each additional level of detail.
A hierarchical code thus bears information on the level of detail of the related class and on the hierarchical relation with its parent class.
This way of coding bears resemblance to the structure of hierarchical databases.
This implies that patient data can be retrieved by using hierarchical codes at a certain level, even when significant extensions or modifications are made at lower levels.
An example are the codes used in ICD-9.

32. 2.4. The Codes
Example of a Four-Digit Code Level in ICD-9 and the Five-Digit Code Level as Extended by the ICD-9-CM

33. 2.4. The Codes
Juxtaposition codes are composite codes consisting of segments. Each segment provides a characteristic of the associated class. for each additional level of detail.
Application: in ICPC a diagnostic code is formed by using a code consisting of one letter of the alphabet (a mnemonic code), followed by a two-digit number.
Example: all codes with the character "D" are related to the tractus digestivus and all codes starting with an "N" describe disorders of the nervous system.
In the example of ICPC, two independent characteristics are coded simultaneously, and each characteristic has its own position in the code.

34. Example of a The Two-Axial ICPC
2.4. The Codes
Example of a The Two-Axial ICPC

35. 2.4. The Codes
Medical procedures can be classified with ordering principles: action, equipment, aim, and anatomical site.
The combination of 100 anatomical sites with 20 different actions, 10 different instruments, and 5 different purposes results in a classification system with a potential of a 100,000 classes and codes.
A way to cope with it is the use of a combination code.
By using a six-digit combination code consisting of four segments, with segments dedicated to action (2 digits), equipment (2 digits), aim (1 digit), and anatomical site (1 digit), respectively, a coding clerk has to distinguish only 135 codes, with which 100,000 combinations can be generated.

36. 2.4. The Codes
In value addition codes in general only powers of 2 are used as a representation of a data item or class.
A several characteristics can be coded. But only one number instead of a segment for each characteristic is used as a code.
Example: we code the presence or absence of risk factors, such as:
- 20 = 1 for smoker / 0 for nonsmoker,
- 21 = 2 for overweight / 0 for no overweight,
- 22 = 4 for increased cholesterol / 0 for not increased cholesterol.
By using the codes 1 to 7 we can sum all the three risk factors mentioned above.

37. 2.5. The Taxonomy
Taxonomy is the theoretical study of classification, including its basic principles, procedures, and rules.
Taxonomy is concerned with classifications in general.
The term classification is used for the end product of the design process.

38. Proposed cognitive taxonomy of medical errors.
2.5. The Taxonomy
Proposed cognitive taxonomy of medical errors.

39. 2.6. The Nosology
Nosology is usually defined as the science of the classification of diseases.
Nosology is usually distinguished from nosography, which is the science of the description of diseases.
Difference between the definition and the description of disease : A disease definition gives only essential characteristics of the disease, whereas a description includes accidental characteristics.

40. 3. Medical Classification Systems
ICD - International Classification of Diseases
ICPC - International Classification of Primary Care
SNOMED - Systematized Nomenclature of Human and Veterinary
DRG - Diagnosis Related Groups
MeSH - Medical Subject Headings
ATC - Anatomic Therapeutic Chemical Code

41. Medical Coding and Classification an organization structure flowchart
The USA
Medical Coding and Classification an organization structure flowchart

42. 3.1. ICD
ICD (International Classification of Diseases ) is the archetypal coding system for patient record abstraction.
The first edition was published in 1900, and it is being revised at approximately 10-year intervals.
The most recent version is ICD-10, which was published in 1992.
Most present registration systems, however, are still based on ICD-9 or its modification, ICD-9-CM

43. 3.1. ICD
ICD consists of a core classification of three-digit codes, which are the minimum requirement for reporting mortality statistics to WHO.
An optional fourth digit provides an additional level of detail.
At all levels, the numbers 0 to 7 are used for further detail, whereas the number 8 is reserved for all other cases and the number 9 is reserved for unspecified coding.

44. 3.1. ICD
The basic ICD is meant to be used for coding diagnostic terms.
ICD-9 as well as ICD-10 also contain a set of expansions for other families of medical terms.
The disease codes of both ICD-9 and ICD-10 are grouped into chapters.
Example: for tuberculosis the three-digit codes 010 to 018 are used in ICD-9, and the codes A16 to A19 are used in ICD-10.
The U.S. National Center for Health Statistics published a set of clinical modifications to ICD-9, (ICD-9-CM). It contains an extra level of detail where needed and also include a volume III on medical procedures.

45. 3.1. ICD
Example of a Four-Digit Code Level in ICD-9 and the Five-Digit Code Level as Extended by the ICD-9-CM

46. Example of a ICD-9-CM coding helper software

47. 3.2. ICPC
The World Organization of National Colleges, Academies and Academic Associations of General Practitioners/Family Physicians (WONCA) did not accept ICD-9, but came up with its own classification - ICPC - International Classification of Primary Care.
ICPC is a two-axis system. The first axis, primarily oriented toward body systems (the tracts), is coded by a letter, and the second axis, the component, is coded by two digits. The component axis contains seven code groups.
Example: the diagnosis pneumonia is coded R81 (R for respiratory tract and 81 for the diagnostic component).

48. 3.2. ICPC
ICPC is used to encode encounters structured according to the SOAP principle:
S for subjective information, e.g., complaints; O is for objective information, e.g., test and lab results; A is for assessment, e.g., diagnosis; and P is for plan, e.g., diagnostic tests, treatment, etc.
An a way to organize patient-oriented information is by disease episodes. ICPC can be used to organize the registration of a disease episode over time, from its onset to its resolution. A disease episode may include several encounters. Each problem in an encounter should be coded separately.

49. Example of a The Two-Axial ICPC

50. 3.3. SNOMED
SNOMED (Systematized Nomenclature of Human and Veterinary) was first published in 1975 and was revised in 1979.
SNOMED is also a multiaxial system. SNOMED II was a code with 7 axes, and SNOMED International has 11 axes or modules. Each of these axes forms a complete hierarchical classification system.

51. 3.3. SNOMED
A diagnosis in SNOMED may consist of a topographic code, a morphology code, a living organism code, and a function code. When a well-defined diagnosis for a combination of these four codes exists, a dedicated diagnostic code is defined.
For example, the disease code D (Pneumococcal pneumonia) is equivalent to the combination of:
T (topology code for Lung, not otherwise specified),
M (morphology code for Inflammation, not otherwise specified), and
L (for Streptococcus pneumoniae) along the living organism axis.

52. The 11 Axes of SNOMED International

53. 3.3. SNOMED infective pneumonia  Harder to comprehend
polyhierarchy
explicit relations
explicit qualifiers
Harder to comprehend
Harder to implement
Harder to maintain

54. 3.4. DRG
DRG (Diagnosis Related Groups ) classification is based on ICD-9-CM codes and other factors not included in ICD-9.
The grouping of ICD codes is based on factors that affect the cost of treatment and the length of stay in the hospital, such as severity, complications, and type of treatment.
The resulting classes are homogeneous with respect to costs and they are medically recognized.
DRGs may thus be used for budgeting.

55. 3.4. DRG
DRG Example

56. 3.5. MeSH
The Medical Subject Headings (MeSH) classification is developed and maintained by the National Library of Medicine (NLM) in the USA.
It is generally used to index the world medical literature.
Within the hierarchy of MeSH, a concept may appear as narrower concepts of more than one broader concept.
Example: Pneumonia is listed as a respiratory tract infection as well as a lung disease.

57. 3.5. MeSH
MeSH Example

58. MeSH in the PubMed Service search result example

59. 3.6. ATC
Anatomic Therapeutic Chemical Code (ATC) has been developed for the systematic and hierarchical classification of drugs.
ATC is an acronym for anatomical (A), the organ system in the body for which the drug is given; therapeutic (T), the therapeutic purpose for which the drug is used; and chemical (C), the chemical class to which the drug belongs.

60. 3.6. ATC
In the early 1970s, the Norwegian Medicinal Depot expanded the existing three-level anatomic and therapeutic classification system of the European Pharmaceutical Market Research Association and added two chemical levels.
Later, the WHO Drug Utilization Research Group accepted the ATC classification as a standard.
Presently, the WHO Collaborating Center for Drug Statistics Methodology in Oslo is responsible for maintaining the ATC codes.

61. 3.6. ATC The advantages of the ATC are as follows:
It identifies a drug product, including the active substance, the route of administration, and if relevant, the dose;
It is therapeutically as well as chemically oriented, a feature that most other systems lack;
Its hierarchical structure allows for a logical grouping;
It is accepted as the international WHO standard for drug utilization research.
A disadvantage is that it does not cover combination products, dermatological preparations, and locally compounded preparations

62. Five Levels of the ATC Code Illustrated by the Code for Furosemide

63. Conclusion
There are many overlapping classifications not only for the coding of diagnoses but also for the classification of medical events.
Although most diagnostic coding systems try to be compatible with the ICD family, ICD itself represents only a limited view and is unable to fulfill the needs of all users.
Systems such as SNOMED have much more expressive power than the more rigid systems such as ICD-9-CM.
Wide acceptance of a coding system is essential for the development of decision-support systems.
International institutions such as WHO with its recognized collaborating centers play an important role in the standardization process