The inclusion criteria in ICPC contain the minimum requirements for that diagnosis. Criteria are NOT meant as a diagnostic tool, but rather as a tool to assign the correct code.

Introduction

It has always been clear to the WONCA Classification Committee that an internationally agreed list of rubrics to classify problems met in primary care would not in itself ensure the highest level of statistical comparability. In the International Classification of Health Problems in Primary Care (ICHPPC-2-defined) published in 1983 inclusion criteria for the use of each rubric were introduced to improve consistency of coding5.

Inclusion criteria are not the same as definitions. They should be considered in relation to their purpose, to improve consistency of coding, rather than as definitions for delineating health problems. We have, however, tried to ensure that they are compatible with accepted definitions, such as those in the International Nomenclature of Diseases (IND).

In this publication many of the inclusion criteria originating in ICHPPC-2-Defined have been updated and are directly related to ICPC rubrics. In some instances, new or extensively modified inclusion criteria have been created based on the theoretical framework described in the next section. Although this publication marks an advance in the taxonomy of general/family practice, it is not yet ideal. ICPC is a classification very much in evolution, and experience with the inclusion criteria presented in this volume will undoubtedly lead to further refinement in the years to come. We welcome comments from users.

Theoretical framework for assignment of inclusion criteria

The theoretical framework used to assign inclusion criteria in this classification is based on the presence of four general categories of diagnosis in primary care: aetiological and pathological disease entities, pathophysiological conditions, nosological diagnoses (syndromes), and symptom diagnoses. It was decided to apply different principles to each category based on its characteristics.

  • aetiological and pathological: the diagnosis has proven pathology or aetiology; inclusion criteria are based on standard disease definition, with modification where necessary to allow application to general/family practice.

Examples: appendicitis, acute myocardial infarction

  • pathophysiological: the diagnosis has a proven pathophysiological substrate; inclusion criteria include symptoms, complaints, and characteristic objective findings.

Examples: presbyacusis, hypertension

  • nosological: the diagnosis depends on a symptom complex based on consensus between physicians, without a proven pathological or pathophysiological base or aetiology, and is often called a syndrome; inclusion criteria include only symptoms and complaints.

Examples: depression, irritable bowel syndrome

  • symptom: a symptom or complaint is the best medical label for the episode.

Examples: fatigue, eye pain

The criteria

The underlying principle used was to provide THE MOST CONCISE INCLUSION CRITERIA POSSIBLE WHICH WOULD MINIMIZE VARIABILITY IN CODING. Adherence to this principle led to the use of minimal inclusion criteria for each rubric. This requires further explanation.

For most diagnostic rubrics, the reader will find one or more criteria which must be fulfilled to code a problem under that title. Sometimes there is a choice of criteria; at other times criteria from a list must be met. When “or” is used in a list it is with its inclusive meaning, which is the same as “and/or”. “Multiple” in this book means three or more.

Attempts were made to specify the minimum criteria needed in order to reduce the complexity of coding and thus minimize miscoding. In addition, we have only included those criteria which have sufficient discriminatory value to distinguish one rubric from another with which it might be confused. In some cases, the available criteria may be too few to exclude all other possible conditions which might be coded mistakenly to a particular rubric, but they will exclude the common ones.

The criteria have whenever possible been based on clinical criteria, rather than requiring the results of tests and investigations. They are as far as possible independent of technology, which varies considerably throughout the world, and is rapidly changing. This makes them appropriate for primary care use throughout the world.

This approach is very different from that seen in classic disease-oriented textbooks , which usually list all signs and symptoms, or all potential criteria, associated with a particular diagnostic title. We believe that in order to maximise the utility of criteria-based problem coding in general practice, brevity must supersede exhaustiveness.

Sometimes the rubric title is itself adequately specific. In these cases, no inclusion criteria are given. To avoid errors, each rubric, with inclusion and exclusion terms, and inclusion criteria, should be read in its entirety.

Attempts were not made to provide criteria for every rubric, particularly residual rubrics, which contain too many disparate diagnoses for useful definition. In these cases, the reader should consult the list of diagnoses included in the rubric title and inclusion terms, or refer to the more complete list given for the relevant rubrics in ICD-10.

Cross referencing

As well as inclusion criteria, each rubric may have the following information:

  • includes: a list of synonyms and alternative descriptions which are included in the rubric
  • excludes: a list of similar conditions which should be coded elsewhere, with the appropriate code for each
  • consider: a list of rubrics with their codes, usually less specific, which might be considered if the particular patient’s condition does not meet the inclusion criteria

Advantages of this framework

The use of this framework results in clear and generally accepted inclusion criteria for problems which are common in general/family practice, and which require inclusion criteria if they are to be coded consistently.

Another major advantage of this framework is that employing minimal inclusion criteria results in coding procedures which are easy to learn and apply in the real world of general/family practice. This will reduce the magnitude of the problem of intercoder variation.

Using inclusion criteria

Inclusion criteria SHOULD NOT be used when recording patient reason for encounter, since these should be coded in terms of what the doctor understands the patient to say, irrespective of whether or not the patient is “correct”.

Inclusion criteria SHOULD be used when coding the diagnoses or problems the doctor manages. Even when the problem has to be coded only as a symptom or complaint, some guidance may be needed in order to select the most appropriate code. For example, feeling faint (N17) is not coded in the same rubric as actual fainting (A06); and abdominal pain may be generalised (D01), epigastric (D02) or localised in other regions (D06). The options need to be clear to users so that the most appropriate alternative is used.

Applying the criteria at different stages of the problem

The inclusion criteria are primarily designed to code the early presentation of a problem. If the problem is to be coded during a later encounter (after its modification by time or therapy) the coder should consider the historical information (eg. blood pressure may well be normal at later consultations in a patient with hypertension receiving therapy but the condition would still be coded as hypertension).

Disadvantages of the system

Clearly, this system of inclusion criteria is not without hazard. In order to improve the accuracy and reliability of statistics from general/family practice, hard edges have been put to diagnostic concepts, many of which seem, in reality , to have blurred borders. Although sharp borders may not be needed for therapy or management, accurate data are needed for purposes of research. The use of hard-edged inclusion criteria may increase the content of residual less specific rubrics, but this is preferred to making most rubrics non-specific. For coding problems which do not fully meet the given criteria, less specific alternatives are suggested following “Consider:”. These suggestions are in addition to those items which are listed as exclusions in the rubric.

Some possible misconceptions

It is important that reader clearly understand several things which the criteria are NOT intended to do.

  1. They do not serve as a guide to diagnosis. The primary purpose of the classification is to reduce chances of miscoding after a diagnosis has been made, and not to eliminate the possibility of diagnostic error. The assumption is that the user will have considered the differential diagnosis prior to the time of coding. In most cases good practice of medicine requires far more information than is given in the inclusion criteria to make accurate diagnoses.
  2. They do not set standards for care. Although information derived from the use of the classification may change medical concepts and ultimately impact on standards of care, these inclusion criteria are intended solely to improve the quality of data recording.
  3. They do not act as a guide for therapy. The criteria given for inclusion or exclusion for a condition do not necessarily relate to the criteria for use of various therapies. For example, the practitioner may well decide that therapy for migraine is indicated in a patient whose findings were insufficient to fulfill the criteria listed under that diagnostic title, and whose condition is coded as “headache”.

Sources

The Committee felt no compulsion to devise new definitions and based inclusion criteria on existing ones, if appropriate for the objectives given above. In fact, few existing definitions did meet those requirements because most had been prepared for research projects rather than for clinical practice and so tended to be rather cumbersome. However, the inclusion criteria included here are compatible with most standard definitions of diseases.

If someone else’s work has been used inadvertently without acknowledgment, apologies are given: imitation is the sincerest form of flattery.