CO-39 denial code
Services denied at the time authorization was requested
How to fix it
This is an adverse determination rather than an administrative error. Appeal on medical necessity against the payer's own policy criteria.
How to prevent it
Where authorisation is refused, decide before delivering the service. Proceeding anyway converts a clinical dispute into a write-off.
In practice
A practice requests authorisation for an advanced imaging study. The plan refuses it. The study is performed anyway because the physician judges it necessary, and the claim returns CO-39.
This is not a paperwork failure. Authorisation was sought through the correct channel and the plan made an adverse determination on the merits, which means the dispute is clinical rather than administrative.
The appeal has to engage the plan's own published criteria for the service and show the patient met them, with the clinical record attached. Arguing that the physician believed it necessary, without mapping that judgement onto the criteria the plan actually applies, is the appeal that gets upheld against you.
What sits behind it
Distinguishing this from a missing authorisation changes the entire approach. CO-197 and its neighbours mean nobody asked; CO-39 means somebody asked and was told no. The first is often recoverable with a retroactive request, the second never is, because the plan has already considered and declined it.
The decision that matters is made before the service, not after. Once a determination has been refused, proceeding converts a clinical disagreement into a financial exposure the practice is likely to carry, and the patient should be part of that decision rather than learning about it from a bill.
Where the service genuinely cannot wait, an advance notice signed before delivery preserves the option of billing the patient. Peer-to-peer review is also worth exhausting first — a conversation between the ordering physician and the plan's reviewer reverses more determinations than a written appeal does, and it happens in days rather than weeks.
Related codes
Terms used here — Prior Authorization · Medical Necessity · Appeal
How we handle it — Prior Authorization · Denial Management · Patient Support
Primary sources
The rules behind CO-39, at the bodies that publish them.
- CMS Interoperability and Prior Authorization Final Rule (CMS-0057-F) (opens in a new tab)
Centers for Medicare & Medicaid Services — The rule imposing prior authorization decision timelines and API requirements on impacted payers. It is the single largest scheduled change to authorization workflow this decade.
- Medicare Coverage Database (LCD/NCD) (opens in a new tab)
Centers for Medicare & Medicaid Services — Searchable national and local coverage determinations. The direct answer to whether a diagnosis supports medical necessity for a given procedure.
- Medicare Claims Processing Manual (opens in a new tab)
Centers for Medicare & Medicaid Services — The operative manual for how Medicare claims must be coded, submitted, adjusted and appealed. When a payer policy and a vendor's advice disagree, this settles it.
Looking for a different code? Search all 190 CARC and RARC codes
Questions about CO-39
A missing authorisation means the request was never made, and plans frequently allow a retroactive request to cure it. CO-39 means the request was made and refused on clinical grounds. The determination already exists, so the only route is appeal against the criteria the plan applied.
Usually yes, and before a written appeal. A direct conversation between the ordering physician and the plan's medical reviewer resolves more adverse determinations than paper does, partly because clinical nuance travels badly in writing and partly because it happens within days rather than weeks.
Only where they were told before the service and agreed in writing to accept responsibility. A signed advance notice obtained before delivery preserves that option. Without it, most contracts prohibit billing the patient for a service the plan declined to authorise.
Find out what your denials are costing you
A free billing audit reviews your denial rate, AR aging and clean claim rate against industry benchmarks. Takes about two minutes to request. No sales pitch.
No setup fees · You pay when we collect · Pricing from 3% of net collections