OM, perhaps you’re thinking about ICD-10-PCS (ICD-10 Procedure Coding System).

You’re right, for procedures, ICD-10-PCS is a compositional system and nothing like the procedure codes in Volume 3 of ICD-9-CM.

However, for diagnoses, the structure of ICD-10-CM has not changed from ICD-9-CM.

E08.331 Diabetes mellitus due to underlying condition with moderate nonproliferative diabetic retinopathy with macular edema

E08.339 Diabetes mellitus due to underlying condition with moderate nonproliferative diabetic retinopathy without macular edema

These codes are pre-compiled combinations of two diseases (diabetes mellitus due to underlying condition and non-proliferative diabetic retinopathy), a severity modifier for one of the diseases (moderate applies to retinopathy), and the presence vs. absence of a manifestation of one of the diseases (macular edema is a manifestation of the retinopathy).

I did not in any “build” or “compile” these ICD-10-CM codes out of more basic units. Nor did anyone else.

I copied and pasted them directly from their pre-compiled glory right out of the PDF file that is the official release format of the 2007 ICD-10-CM draft.

I give proof at the Better Diagnosis Coding blog that NCHS creates and maintains ICD-10-CM using a word processor!

It has hierarchical codes, NOS and NEC codes, a maximum of 10 children for each non-leaf code, and so on.

I wonder if you could give me an example of what you mean. There is no compositionality at all.

What character in what position identifies all patients with diabetic retinopathy, for example?

The answer is that you can’t identify all patients with diabetic retinopathy in that manner.

What is the set of rules or syntax for composing an ICD-10-CM code?

The medical content (ie, new diseases) in ICD-10-CM is updated, but you can’t possibly say the technical structure underlying ICD-10-CM is any different than ICD-9-CM.

NCHS delivers ICD-10-CM as a 23MB, free-text blob. You can’t even import it into a database table!

Spero-Melior, I don’t know what you are trying to say. ICD-9 is a pre-compiled coding system. ICD-10 is not, so to talk about the number of codes in each system is irrelevant. An electronic medical record could theoretically code the ICD-10 code from clinical information in the EMR without the physician having to actually choose a specific code. This is much more difficult using ICD-9, precisely because it is pre-compiled.