Happy October 1st, Fellow Coding Geeks

October 1 is a holiday for us medical coding geeks (a small, nerdy holiday, but a holiday). The new fiscal-year code set takes effect that day, and this year it adds 190 codes, deletes 30, and revises 4. Picture Christmas morning with a conversion table under the tree.

There's no grace period: a visit on September 30 is coded with the old set, and one on October 1 gets the new one. Billing offices spend the day fixing pick lists, because a claim carrying a deleted code gets rejected. I42.0, dilated cardiomyopathy, is one of this year's casualties, replaced by I42.00, I42.01, and I42.09. The whole ICD-10 system went live on an October 1 back in 2015.

The new code I keep coming back to is for medetomidine, a veterinary sedative that has been turning up mixed into illegally made fentanyl. The CDC says the people buying those products may not know it's in there. It's the suspected cause of a withdrawal syndrome that put 165 people across three Philadelphia health systems in the hospital between September 2024 and January 2025, and 91% of them went to an intensive care unit while 24% were intubated.

As of October 1, ICD-10-CM has toxic effect codes for it, T65.85-, split by intent (accidental, self-harm, assault, undetermined) and by encounter type.

According to a recent review in Current Addiction Reports, standard hospital toxicology panels don't test for medetomidine. A coder assigns what the provider writes in the chart, so the first year of data will reflect the clinicians who thought to look.

The withdrawal syndrome that put those patients in ICU beds has no code of its own yet. A medetomidine withdrawal proposal was on the committee's March 2026 agenda, and that same review says a distinct code is still under consideration.

The CDC announces any April 1 additions in November, so that's when I'll find out whether a medetomidine withdrawal code is on the way. Until then, I'm enjoying the holiday. Happy October 1st, fellow coding geeks.