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Coding and Classification
Lection 1
Basic Questions
Introduction to classification
Classification basics
Medical Classification Systems
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 illdefined and are perhaps even ambiguous.
1. Introduction to classification
Computers have the potential to improve
legibility, accessibility, and structure, but
these pose heavy demands on the data
collection.
It is posible with development and
application of an electronic patient
record (also sometimes called electronic
healts record - EHR).
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
2. Classification basics
Classification definftion
Purpose and concepts
Ordering Principles
Nomenclatures and Thesauri
Codes
Taxonomy
Nosology
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.
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
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.
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).
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.
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
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.
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.
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.
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.
2.3. Ordering Principles
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.
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.
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.
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.
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.
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.
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. For
example, hospital departments are often
indicated by a mnemonic code, such as ENT
for the Department of Ear, Nose, Throat,
CAR for Cardiology, or OB-GYN for the
Department of Obstetrics and Gynecology.
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.
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.
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.
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.
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.
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.
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
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-9CM
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.
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, (ICD9-CM). It contains an extra level of detail where needed
and also include a volume III on medical procedures.
3.1. ICD
Example of a Four-Digit Code Level in ICD-9 and the FiveDigit Code Level as Extended by the ICD-9-CM
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).
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.
3.2. ICPC
Example of a The Two-Axial ICPC
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.
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-13510
(Pneumococcal pneumonia) is equivalent to the
combination of:
T-28000 (topology code for Lung, not otherwise
specified),
M-40000 (morphology code for Inflammation, not
otherwise specified), and
L-25116 (for Streptococcus pneumoniae) along
the living organism axis.
3.3. SNOMED
The 11 Axes of SNOMED International
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.
3.4. DRG
DRG Example
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.
3.5. MeSH
MeSH Example
3.5. MeSH
MeSH in the PubMed Service search result example
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.
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.
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
3.6. ATC
Five Levels of the ATC Code Illustrated by the
Code for Furosemide
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