I take a view of ICD-9-CM codes as diagnostic statements, where these statements are about entities that exist in reality. I then represent these entities according to a realist view of disease, disorder, and diagnosis as defined by the Ontology for General Medical Science and using Referent Tracking templates. I illustrate the approach using ICD-9-CM codes that refer to systemic arterial hypertension. The approach is general and could help enable interoperability of data encoded with realist ontologies and data encoded with terminologies and administrative classifications, such as data from electronic health records and insurance claims.
Bodenreider et al. note that the term Tuberculosis of adrenal glands, tubercle bacilli
not found (in sputum) by microscopy, but found by bacterial culture is a sentence
schema that contains information about how the disease was diagnosed, which has no
bearing on the disease itself or the type of which it is an instance [
The ICD-9-CM Official Guidelines for Coding and Reporting document lends credence
to this view. First, it uniformly refers to ICD-9-CM codes as diagnosis codes, not
disease codes [
Besides combination codes, the existence of epistemological criteria in ICD-9-CM also supports the diagnosis perspective on ICD-9-CM. For example, all codes starting with 010 through 018 are differentiated by the manner in which tuberculosis was diagnosed (e.g., tubercle bacilli found (in sputum) by microscopy). A realist-based ontology should not have an exact match for these codes because they contain an epistemological criterion. Thus, conversion of these codes to a realist representation is more complex than a simple assertion of equivalence among codes.
statements about? As the name of the classification suggests, they are about diseases, at least. We take the realist view that distinguishes carefully between a diagnosis, a disorder, and a disease. In this view, diagnostic statements refer to diseases, disorders, and possibly other entities that exist in reality (which in the case of ICD-9-CM, include symptoms, findings, and epistemological methods).
representations of the entities to which ICD-9-CM codes as diagnostic statements—or perhaps more generally clinical statements—refer. That is, when a clinician assigns an
using the Referent Tracking (RT) paradigm [
query for type 2 diabetes mellitus using DOID:9352 from the Disease Ontology (DO) will not return patients whose type 2 diabetes mellitus is recorded using only ICD-9
particulars in a given patient that are referred to by ICD-9-CM codes relating to systemic arterial hypertension. These data are the most common form of diagnostic data, occurring in electronic medical records (EMRs) and insurance claims data. I also describe an implementation of the approach in the RT paradigm. The approach is general and could be applied to ICD-10-CM and terminologies like SNOMED-CT.
2.1. Selecting a subset of ICD-9-CM
I searched the tabular list of the current version of ICD-9-CM on the word
‘hypertension’, selecting only codes that represent statements about systemic arterial
hypertension. Hypertension is the most common chronic condition that results in visits
to physician offices [
Ocular hypertension, 416.0 Primary pulmonary hypertension, 459.3 Chronic venous hypertension (idiopathic), and all codes beginning with 642 Hypertension complicating pregnancy, childbirth, and the puerperium. 2.2. ICD-9-CM diagnoses of hypertension and related conditions
directly (e.g., essential hypertension) or indirectly (e.g., hypertensive heart disease) that the patient suffers from systemic arterial hypertension.1 This set excludes 55 ICD-9
and childbirth.
A key issue was how to treat ICD-9-CM codes with the phrases ‘unspecified’ or ‘not
elsewhere classified’ in their title. Although one could handle ‘unspecified’ and ‘not
elsewhere classified’ in the RT paradigm, I did not. Typically, ICD-9-CM codes are
assigned within the context of a single chart, and thus the ‘unspecified’ reference refers
to statements made within only that chart. Indeed, the ICD-9-CM Guidelines
specifically state codes … titled “unspecified” are for use when the information in the
medical record is insufficient to assign a more specific code [
organizations within a community, it would be inappropriate to include templates that deny the presence of other templates within the larger community as a whole.
2.3. Definitions of disease, disorder, and diagnosis
Disorder: A material entity which is clinically abnormal and part of an extended organism. Disorders are the physical basis of disease. Disease: A disposition (i) to undergo pathological processes that (ii) exists in an organism because of one or more disorders in that organism. Diagnosis: The representation of a conclusion of an interpretive process that has as input a clinical picture of a given patient and as output an assertion … to the effect that the patient has a disease of such and such a type.
disposition to undergo a particular pathological process. Note that absence of realization of the disposition (e.g., in the presence of medications that maintain blood
http://spreadsheets.google.com/ccc?key=0AnlWz1vGIs2hdF9acjBjRWpheG9DWXdw MTFhaGc4NGc&hl=en
pressure in the normal range) does not imply absence of the disease (disposition).
2.4. Representing Hypertension
significant evidence exists that the underlying disorder is an abnormally elevated
quantity of salt in the blood, which itself is the consequence of a wide variety of
disorders that confer a disposition to enhanced reabsorption of salt by the kidneys [
hs instance_of Human dz instance_of Hypertension do instance_of Disorder do part_of hs dz inheres_in hs dz disposition_of do
do instance_of Scattered molecular aggregate
mo instance_of NaCl do has_grain mo pb instance_of Portion of blood do part_of pb pb part_of hs 2.5. Essential vs. Secondary vs. Complication of Treatment
The term ‘essential hypertension’ refers to hypertension where the underlying disorder that disposes to renal salt retention is unknown, whereas secondary hypertension refers
which are instance–universal relations. to cases whose underlying disorders/diseases are known. As an example of the latter, reduced blood flow to the kidney due to stricture or stenosis of a renal artery causes the kidney to retain salt to increase blood pressure (to in turn increase blood flow to itself).
explicitly state the disorder that predisposes to renal retention of salt, we add nothing further. Since the final common pathway of hypertension regardless of these distinctions is elevated salt content of the blood, which in turn results from a different disposition (disease) which in turn has a different physical basis (disorder), these distinctions do not affect our expansions.
There is also an ICD-9-CM code for secondary hypertension resulting from iatrogenesis (i.e., caused by treatment). Here, a disorder was caused by an instance of treatment, giving rise to a disposition to renal salt resorption, whose realization caused the disorder underlying hypertension: tr instance_of Treatment tr results_in do_2 do_2 part_of hs dz_2 disposition_of do_2 dz_2 realized_by sr sr instance_of Exaggerated renal salt resorption sr results_in do 2.6. Benign vs. Malignant Hypertension
to other diseases mentioned such as heart disease, chronic kidney disease, etc. Whether
hypertension is benign or malignant refers to the course of the disease. Malignant
hypertension … is a sudden and rapid development of extremely high blood pressure
[
dc instance_of Acute disease course
dc instance_of Chronic disease course dz realized_by dc 2.7. Hypertensive Heart and Kidney Disease
dz_2 instance_of Heart disease do_2 instance_of Disorder dz_2 inheres_in hs
pp instance_of Pathological process dz realized_by pp pp results_in do_2 ht instance_of Heart do_2 part_of ht ht part_of hs
2.8. Presence vs. Absence of Heart Failure The title of several ICD-9-CM codes refers to the presence or absence of heart failure. ‘Heart failure’ is an ambiguous term that may refer to either a pathological process or the disposition to it. We use ‘heart failure’ in the latter sense, which is consistent with medical usage: we treat heart failure, and when the heart is not malfunctioning, the disposition to undergo malfunctioning remains.
dz_3 instance_of Heart failure do_3 instance_of Disorder dz_3 disposition_of do_3 dz_3 inheres_in pt do_3 part_of ht
pt lacks Heart failure with respect to bearer_of
Ai = < IUIp, IUIa, tap >
Specifically, it …captures the assignment of an IUIp to a particular at time tap by the …
author IUIa [
A1 = <IUIdz, IUIhogan, 5/14/10>
ta is time of authorship, o is the ontology from which the universal u derives, and inst is the instance_of relation from the Relation Ontology (RO):
Ui = < IUIa, ta, inst, o, IUIp, u, tr >
Ex: U1 = < IUIh, 5/14/10, inst, DO, IUIdz, Hypertension, 5/7/10 >
Ri = < IUIa, ta, r, o, P, tr >
Ex: R1 = < IUIh, ta, part_of, RO, <IUIdo, IUIpt>, tr >
any instance of a universal u:
U i = < IUIa, ta, r, o, IUIp, u, tr >
Ex: U1=< IUIh, ta, bearer_of, RO, IUIpt, Heart failure, tr >
Ex: Co1=< IUIh, ta, ICD-9-CM, IUIpt, 401.1, tr >
entities implied by a diagnosis—as outlined above—as an expansion. I use the term ‘expansion template’ to refer to an RT template created to represent these entities and their relationships one another. I propose a new subsystem of the RTS called the ‘expansion subsystem (ESS)’ that performs the expansion. The templates I described above are sufficient to represent all the statements about particulars I have listed here.5
the IUIa from the original PtoCO template that contained the ICD-9-CM code in question. However, this approach would incorrectly assign any errors made in the expansion of the code to that author. Other alternatives include having a single IUIa for the ESS or having a different IUIa for each expansion of a single ICD-9-CM. I adopt a single IUIa for the ESS.
Except for A-templates and Meta-templates (which we do not discuss further here), each template has two timestamps: one to capture the time at which the assertion holds in reality, or tr and one to capture the time at which the assertion was made, or ta. The latter timestamp is straightforward: I simply use the time at which the ESS completed the expansion. For the former timestamp, I use the tr of the PtoCO template, because it is the time at which the diagnostic statement of the ICD-9-CM code holds, and thus the time at which the assertions implied by the ICD-9-CM code hold.
the RTS. The problem of ensuring unique reference of IUIs and potentially merging duplicates is not unique to this work: it is a problem for referent tracking in general. I assume the existence of a solution in the RTS to this problem that the ESS may employ.
or even clinical statements. Using realist definitions of disease and its related entities, and the referent-tracking paradigm, I have enabled representation of the entities in reality referred to by 51 ICD-9-CM codes that imply the existence of hypertension.