Every October 1 the diagnosis code set changes, and every October 1 a handful of claims from every practice go out with a code that stopped existing the night before. The clearinghouse rejects them, or worse, the payer accepts them and denies them three weeks later with CO-16 and a remark about an invalid diagnosis. The fix is never hard. The problem is that nobody owned the calendar.
CMS released the fiscal year 2027 ICD-10-CM files on June 5, 2026, and the CDC's National Center for Health Statistics posted the full set through June. The update adds 190 new reportable codes, deletes 30 and revises four titles. Compared with FY 2026, which added 487 new codes, this is a light year. In our experience light years are more dangerous than heavy ones, because nobody schedules the work. The 30 deletions are where the October rejections will come from, and several of them sit in codes that primary care and cardiology use every day.
Today is July 7. That leaves twelve weeks. Here is how we would spend them.
Key takeaways
- 190 new codes, 30 deleted, four revised, effective for encounters on or after October 1, 2026. Date of service decides which code set applies, not the date you submit.
- Dilated cardiomyopathy I42.0 becomes a non-billable parent with three new children. It is the single most likely cause of rejected cardiology and primary care claims in October.
- Favorites lists, problem lists and order sets do not update themselves when the EHR loads the new table. That is where the deleted codes hide.
- One named owner, a twelve-week calendar and a test claim in September prevent almost all of the trouble.
What actually changed
The changes favor specificity over volume. The clusters that matter most for office practices:
- Chapter 19, injury and poisoning: the largest share, roughly 60 new codes, mostly expanded toxic-effect coding. The S23.420 series for sternoclavicular sprain is among the deletions.
- Chapter 15, pregnancy and childbirth: about 44 new codes. Ectopic pregnancy gets site specificity (cesarean scar, cervical and cornual locations, with laterality where it applies), and a new O31.4- category covers a continuing pregnancy after a vanishing twin, with 33 codes by trimester and fetus.
- Chapter 13, musculoskeletal: about 31 codes. Osteomyelitis at M86.8X- expands by anatomical site, and plantar fasciitis moves to M67.A01 (right foot), M67.A02 (left foot) and M67.A09 (unspecified).
- Chapter 21, Z codes: about 16 codes, including exposure history for burn pit emissions, Agent Orange and blast overpressure, and two new underweight adult BMI codes, Z68.18 (BMI 18.4 or less) and Z68.19 (BMI 18.5 to 19.9).
- Cardiomyopathy: I42.0, dilated cardiomyopathy, is expanded into I42.00 (unspecified), I42.01 (familial-genetic) and I42.09 (other). A new I42.81 covers arrhythmogenic cardiomyopathy, and Brugada syndrome and catecholaminergic polymorphic ventricular tachycardia get their own codes.
- Hereditary cancer syndromes: Lynch syndrome and Li-Fraumeni syndrome get dedicated codes instead of sharing a general genetic susceptibility code.
- Neoplasms: new site-specific codes for secondary malignancy of the larynx (C78.31), pharynx (C78.32) and oral cavity (C79.83). The note between D05 (carcinoma in situ of breast) and C50 changes from Excludes1 to Excludes2, which changes whether the two can appear on the same claim when both are documented.
The official guidelines for FY 2027 carry only minor changes in a year like this; the hypertension section is the one to read closely. Make sure your coders have the FY 2027 version rather than the one they downloaded last October.
The rule that people forget
The date of service, not the date you submit the claim, determines which code set applies. A visit on September 30 coded in October still uses FY 2026 codes. A visit on October 1 uses FY 2027 codes even if the claim is prepared early. Practices with a long charge lag straddle the boundary for weeks, and their coders need both tables open. Facility claims follow discharge date, so a hospital stay that begins September 28 and ends October 2 is coded entirely under FY 2027; your professional claims for the same stay are coded by each visit date. This is where the hospitalist groups get caught every year.
The twelve-week plan
| Weeks | Dates | Work | Owner |
|---|---|---|---|
| 1 to 2 | July 7 to July 20 | Download the FY 2027 tables and the conversion table. Run your top 200 diagnosis codes by volume against the deletion list. List every deleted or demoted code your providers used in the last twelve months, with the count. | Coding lead |
| 3 to 4 | July 21 to August 3 | Ask your EHR and practice management vendor for their release date and whether the update loads automatically. Ask specifically about favorites lists, problem lists, order sets and charge templates, which often do not update with the code table. | Practice manager |
| 5 to 6 | August 4 to August 17 | Write one page per specialty of the new codes that matter, with the old code beside the new one. Cardiology gets the cardiomyopathy page. Podiatry and orthopedics get plantar fasciitis laterality and osteomyelitis sites. OB gets the ectopic pregnancy codes. Primary care gets BMI and cardiomyopathy. | Coding lead |
| 7 to 8 | August 18 to August 31 | Provider education, fifteen minutes per specialty at an existing meeting. Focus on documentation: laterality, site, genetic versus acquired, the BMI value itself. | Coding lead and medical director |
| 9 to 10 | September 1 to September 14 | Load the update in a test environment if your vendor offers one. Send a test claim with a new code through the clearinghouse. Check payer bulletins for edits tied to the new codes, especially for cardiomyopathy and BMI. | Billing lead |
| 11 | September 15 to September 28 | Clean up problem lists: patients with I42.0 as an active problem need a specific code before their October visit. Update prior authorizations that reference a code being deleted. | Clinical staff and authorization staff |
| 12 | September 29 to October 5 | Go-live. Run the rejection report every morning for two weeks and sort by diagnosis-related rejections. | Billing lead |
The favorites list problem
This is the part everyone skips. Most EHRs update the master code table on schedule and leave provider favorites lists, quick picks and problem-list entries alone. A provider who has "dilated cardiomyopathy I42.0" in a favorites list will keep selecting it in October, the EHR may or may not warn them, and the claim will fail. Export each provider's favorites, cross them against the deletion list, and replace the entries before September 30.
A worked example from a fifteen-provider internal medicine and cardiology group we looked at last year. The favorites export ran to 2,100 entries across all providers. Twenty-six of them were codes deleted in the FY 2026 update, and eleven of those had been selected more than 50 times in the prior year. The replacement took one coder an afternoon. Had they skipped it, the rejections would have run at a few dozen a week through October, each one touched by a biller, a coder and sometimes the provider. An afternoon against several weeks of rework is not a close call.
Prior authorizations and orders that cross the line
An authorization approved in August for a procedure scheduled in October may carry a diagnosis code that will not exist on the date of service. Most payers match on the procedure and honor the authorization, but some will not, and the denial reads "diagnosis does not match authorization." Pull the list of open authorizations with service dates after September 30 and check each diagnosis against the deletion list. There are usually fewer than twenty in an office practice.
Standing lab and imaging orders have the same problem. An order for a quarterly A1c or a monitoring echo that carries a soon-to-be-deleted code will produce a claim from the lab or imaging center with an invalid diagnosis, and that denial lands on their desk, not yours, which means you hear about it as a phone call in November. Ask your EHR whether recurring orders can be re-coded in bulk.
Payer edits are the second wave
The first wave of October problems is invalid codes. The second wave arrives in November, when payers finish loading their own edits for the new codes. Medical necessity policies that listed I42.0 as a covered diagnosis for an echocardiogram may not yet list I42.01; a payer's BMI-based policy for nutrition counseling may or may not recognize Z68.18. In the November denial report, filter for CO-50 and CO-11 on claims with new FY 2027 codes and appeal with the crosswalk attached. In our experience payers fix these within a quarter, but only for the practices that point them out.
Questions we hear
Do we need new code books?
You need the current code table loaded in your systems and a reference your coders trust. Whether that is a printed book or a subscription is a preference. What you cannot do is code from memory through the transition, and you cannot rely on the EHR search alone, because the search will happily return a deleted code for a few weeks in some systems.
The update is small this year. Can we skip the provider training?
We would not. The cardiomyopathy and BMI changes require different documentation, not just a different code. A coder cannot add laterality, a genetic etiology or a BMI value that the provider did not write down, and a query for every one of those visits costs more than fifteen minutes at a staff meeting.
Who should own this?
One name. Usually the coding lead, with the practice manager owning the vendor conversation. If nobody in the practice has the hours, our medical coding team runs this calendar for the practices we serve, and the live courses cover the FY 2027 changes in September.
What to do this week
- Download the FY 2027 tables and the conversion table and put them in a shared folder with the date.
- Run your top 200 diagnosis codes against the deletion list and count the visits each deleted code touched in the last year.
- Name the owner and put the twelve-week calendar in writing.
- Email your EHR vendor the four questions: release date, automatic load, favorites lists, order sets.
- Book the fifteen-minute provider sessions for late August now, while the meeting slots are still open.
