Most practices we audit have a denial rate they think they understand. They look at the dashboard, see 6.2% or 8.4%, shrug, and move on. The dashboard is lying to them — not on purpose, but because it's averaging away the codes that hurt the most.
Below are the seven CARC and RARC codes we see most often eat into a clinic's bottom line. None of them are exotic. All of them are recoverable. We've sorted them roughly by how much money they tend to leave on the table for a typical 8–15 provider group.
1. CO-16 — Claim/service lacks information
CO-16 is the lazy person's denial. It almost never means "the claim is wrong." It means "a payer rep glanced at the claim, didn't see one specific thing, and rejected it." The thing is usually a missing modifier (most often 25 or 59), a referring provider NPI, or an authorization number on a service that didn't actually require auth.
If you're seeing more than 8–10 CO-16s per 1,000 claims, you don't have a coding problem — you have a scrubber problem. Most clearinghouse rules engines will catch the modifier-25 with E&M issue, but only if the rule is turned on. Check it.
2. CO-97 — Procedure is bundled into another service
CO-97 is where NCCI edits live. The honest truth: about a third of CO-97s are correct denials — the codes really were bundled. The other two-thirds are recoverable with the right modifier (59, XS, XU, XE, XP) and documentation showing the services were distinct.
The trap is automation. We've seen practices auto-write-off all CO-97s because someone in 2019 said "those are bundled, don't bother." One ortho group we onboarded last year was writing off about $14,000 a month in legitimately appealable CO-97 denials — most of them on imaging done same-day as injections.
3. PR-204 — Service not covered by this payer/plan
PR-204 is technically the patient's responsibility, which is why a lot of billers stop there. They post it to the patient and move on. That's a mistake when the service shouldn't have been delivered without prior auth or when the patient's plan changed mid-encounter.
- Pull the last 90 days of PR-204s grouped by CPT and payer.
- If a single CPT/payer pair shows up 5+ times, that's a coverage gap your front desk doesn't know about.
- Update the eligibility check at scheduling, not at check-in. By check-in, the clinical decision is already made.
4. CO-50 — Not deemed medically necessary
CO-50 is the most expensive denial on this list, dollar-for-dollar, because it almost always lives on high-RVU procedures: imaging, infusions, sleep studies, EMG/NCV. The denial isn't that the service was wrong. It's that the documentation didn't connect the diagnosis to the medical necessity policy.
Look up the LCD or NCD for the procedure before you appeal. Quote the policy by article number in the appeal letter. We've gotten back about 71% of CO-50 appeals when the letter cites the exact LCD section. We get back about 22% when it doesn't. That's not a coding problem. That's a writing problem.
5. CO-45 — Charge exceeds fee schedule
CO-45 is technically not a denial — it's a contractual adjustment. But it's where underpayments hide. If your charge master is set to 250% of Medicare and a payer pays 120%, that's correct. If your contract says 140% and they're paying 120%, that's $20,000–$80,000 a year for a mid-sized group, depending on volume.
6. PR-1 — Deductible amount
Including PR-1 on a denials list will surprise people. It isn't a denial. It's the patient's deductible. We include it because it's the most under-managed bucket in patient AR. Practices send a statement, wait 30 days, send another, wait 30 days, send a third, then write off.
By the time a third statement goes out, the patient has forgotten what the visit was for. Collect the deductible at point of service whenever the eligibility check shows it's unmet. Yes, it's awkward. It also lifts patient collection rates by 30–50% in our experience.
7. CO-197 — Precertification/authorization absent
CO-197 is the one denial code where prevention is everything. Once you have a CO-197, your appeal options are slim — most payers won't grant retro-authorization unless there's documented urgency. The fix is upstream: a real prior-auth workflow with a single owner, not "whoever is at the front desk that day."
We tell clients to look at their CO-197s and ask one question: did anyone on staff own this auth before the patient walked in? If the answer is no, that's the work. The denial is just a symptom.
What to actually do this week
- 1Pull a denials report by CARC code for the last 90 days, grouped by payer.
- 2Sort by total dollars — not count. The biggest count and the biggest dollars are rarely the same code.
- 3Pick the top three by dollars. Build a one-page playbook for each: what's the root cause, who owns the fix, what's the appeal template.
- 4Re-pull the report in 60 days. If denials in those three categories haven't dropped at least 30%, the playbook isn't being used.
Denials aren't a moral failing. They're a process output. Fix the process and the dashboard takes care of itself.