By: Charlie Harp

What seems to be the Problem? International Classification of Diseases (ICD)

International Classification of Diseases is a publication from the World Health Organization (WHO) and it provides a number of vocabularies for expressing disease concepts.

The history of the ICD is available here.

ICD-9-CM

The International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) is based on the World Health Organization’s Ninth Revision, International Classification of Diseases (ICD-9).

ICD-9-CM is the official system of assigning codes to diagnoses and procedures associated with hospital utilization in the United States.

The structure of  ICD-9-CM codes is relatively straight forward. The code itself is an explicit hierarchy with the primary disease characteristic typically represented by the first part of the code and the secondary characteristics grouped in numeric sequence in the second part of the code.

As you can see in the example below you should always treat the ICD-9-CM code as text and not a numeric as numeric interpretation of the code would be a disaster.

Below are the ICD-9-CM codes representing ‘hypertensive chronic kidney disease’:

403             Hypertensive chronic kidney disease403.0          Hypertensive chronic kidney disease, malignant
403.00        Hypertensive chronic kidney disease, malignant, with chronic kidney disease stage I through stage IV, or unspecified
403.01        Hypertensive chronic kidney disease, malignant, with chronic kidney disease stage V or end stage renal disease
403.1           Hypertensive chronic kidney disease, benign
403.10        Hypertensive chronic kidney disease, benign, with chronic kidney disease stage I through stage IV, or unspecified
403.11        Hypertensive chronic kidney disease, benign, with chronic kidney disease stage V or end stage renal disease
403.9           Hypertensive chronic kidney disease, unspecified
403.90        Hypertensive chronic kidney disease, unspecified, with chronic kidney disease stage I through stage IV, or unspecified
403.91        Hypertensive chronic kidney disease, unspecified, with chronic kidney disease stage V or end stage renal disease

Note: This manner of establishing codes is less than ideal. A smart code is a identifier that implies meaning through its structure. Typically this manner of establishing codes becomes fraught with issues as a coding scheme becomes more complex over time. For example, there is not a very good way to express a disease or procedure in ICD-9 if it belongs in more than one place in the hierarchy (poly-hierarchical) without creating duplicate concepts (which is bad).

There are roughly 22,000 ICD-9-CM codes.

The ‘Home Page’ of ICD-9-CM is https://www.cdc.gov/nchs/icd/icd9cm.htm

Wikipedia has a fairly robust ICD-9 list and reference capability here:https://en.wikipedia.org/wiki/List_of_ICD-9_codes.

Like all public standards is not provided in a format that makes it easy to use. The downloads that are available via FTP are rich text files that are human readable that are not easy to parse into a typical application consumable vocabulary file.

There are a number of web sites that providing search and lookup tools for ICD-9 but the only source of free coded ICD-9-CM codes (that I have found) is the UMLS metathesaurus (also not easy…).

If you want easy and well structured you need to pay…

I recommend Ingenix at the following link.

ICD-10-CM

Like ICD-9-CM, ICD-10-CM is based on the World Health Organization ICD-10 coding system. ICD-10 is designated to replace ICD-9 and is a more granular terminology (actually more like SNOMED-CT).

The structure of ICD-10-CM is different than ICD-9. The codes are alphanumeric where the initial alpha code delineates the codes into 22 chapters.

Below are the ICD-10-CM codes representing ‘hypertensive chronic kidney disease’:

I120              Hypertensive chronic kidney disease with stage V chronic kidney disease or end stage renal disease
I129              Hypertensive chronic kidney disease with stage I through stage IV chronic kidney disease, or unspecified chronic kidney disease
There are roughly 68,000 ICD-10-CM codes.

The structure of the ICD-10 that is as is depicted below (thanks to the AHIMA website).

There is a good primer on the differences between ICD-9 and ICD-10 on the AHIMA website here.

The ‘Home Page’ of the ICD-10-CM.

Wikipedia has a fairly robust ICD-10-CM list and reference capability here.

RTF was apparently too easy as ICD-10-CM is published as a PDF file…

ICD-10-CM can also be pulled from the UML Metathesaurus and purchased in convenient formats from Ingenix.

SNOMED-CT

SNOMED CT (Systematized Nomenclature of Medicine–Clinical Terms) is a comprehensive clinical terminology, originally created by the College of American Pathologists (CAP) and, as of April 2007, owned, maintained, and distributed by the International Health Terminology Standards Development Organization (IHTSDO).

SNOMED-CT codes do not have a hierarchical code, like the ICD vocabularies. Rather, SNOMED-CT creates meaningless identifiers and relates them to each other in a directed acyclic graph or DAG (which is where the phrase DAG-gumit! originiated… I am pretty sure). This means that any term in the vocabulary can be related to zero-to-many terms, as long it is cannot end up being its own parent. The relationships themselves are separate from the SNOMED-CT code.  SNOMED-CT also separates the notion of concepts and descriptions (or concept synonyms).

Below are the ICD-10-CM codes representing ‘chronic kidney disease’:

431855005|disorder|Chronic kidney disease stage 1

431856006|disorder|Chronic kidney disease stage 2

433144002|disorder|Chronic kidney disease stage 3

431857002|disorder|Chronic kidney disease stage 4

433146000|disorder|Chronic kidney disease stage 5
There are roughly 68,000 active disorder concepts in SNOMED-CT.

I have created a number of posts (and a few screencasts) on SNOMED-CT so I would first direct you to earlier posts in this blog.

The main NLM page for SNOMED-CT is located here: https://www.nlm.nih.gov/research/umls/Snomed/snomed_main.html

The SNOMED-CT user’s guide is downloadable here: https://www.ihtsdo.org/fileadmin/user_upload/Docs_01/SNOMED_CT/About_SNOMED_CT/Use_of_SNOMED_CT/SNOMED_CT_User_Guide_20090731.pdf

The main CAP page for SNOMED-CT is located here: https://www.cap.org/apps/cap.portal?_nfpb=true&_pageLabel=snomed_page

The Wikipedia page for SNOMED-CT is located here: https://en.wikipedia.org/wiki/SNOMED_CT

You can download SNOMED-CT release files from the NLM site here:
https://www.nlm.nih.gov/research/umls/licensedcontent/snomedctfiles.html

Note:  to download NLM data files, like SNOMED-CT, you need to register and obtain a license from the NLM.  You can do that here https://wwwcf.nlm.nih.gov/umlslicense/snomed/license.cfm

The next post will cover procedure terminologies.