Sunday, January 18, 2009

Myth: SNOMED CT has more disease codes than ICD-10-CM

Because SNOMED CT is a reference terminology, and ICD-10-CM a disease classification, one might think that SNOMED CT would have more disease codes because it reaches a higher level of diagnostic precision (what the ICD-10-CM proponents ambiguously refer to as "specificity") than ICD-10-CM.

One would be wrong, however. We already busted this myth in a previous post, but we give it its own post to highlight the absurdity that is ICD-10-CM.

Per the final rule (warning: pdf) to adopt ICD-10-CM, ICD-10-CM has approximately 68,000 codes. SNOMED CT (the July, 2008 version), by contrast, has 63,731 active disease codes.

ICD-10-CM therefore has approximately 7% MORE disease codes than SNOMED CT. Assuming of course, that ICD-10-CM contains only codes for diseases, which it doesn't. It has codes for lots of other things, like symptoms of disease. If there were any way to count automatically how many ICD-10-CM codes represented diseases as opposed to something else, it would be possible to do an actual apples-to-apples comparison.

But, since ICD-10-CM says it classifies diseases (and not other things) and gives no way to infer automatically (i.e., by computer) whether it classifies other things than disease, we feel justified in making this comparison. It highlights another absurdity of ICD-10-CM: it isn't (entirely) what it says it is.

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