Roughly 5–10% of medical claims get denied on first submission. Across a practice, that’s a meaningful number - and across the industry, it’s billions of dollars in rework and write-offs every year. The good news: most denials fall into a handful of repeatable categories. Understand the 7 that cause the most damage and you can prevent the majority of them.
1. Eligibility and coverage issues
What it is: The patient’s insurance isn’t active, doesn’t cover the service, or isn’t what’s on file.
This is the #1 cause of denials in most practices. Patients change jobs, lose coverage, switch plans, and forget to tell you. If your intake process doesn’t verify eligibility in real time before the visit, you’re gambling on every claim.
Typical denial codes: CO-27 (expenses incurred after coverage terminated), CO-31 (patient cannot be identified as our insured), PR-177 (patient has not met deductible).
How to prevent it:
- Run eligibility checks 48 hours before the appointment, then again at check-in
- Use real-time 270/271 eligibility transactions, not payer portals
- Flag plans with high-deductible structures for patient payment collection at the visit
- Re-verify for any return patient who hasn’t been seen in 60+ days
Eligibility denials are almost entirely preventable. They’re also the cheapest to fix - most take minutes if caught immediately and days if caught weeks later.
2. Missing or incorrect patient information
What it is: A typo in the patient’s name, DOB, insurance ID, or policyholder info causes the payer to reject the claim.
Payer systems are literal: “Jon Smith” and “John Smith” are different patients. A transposed digit in a subscriber ID, a date of birth off by a year, a maiden name instead of current last name - any of these will bounce a claim.
Typical denial codes: CO-16 (claim lacks information), CO-140 (patient/insured health identification number and name do not match).
How to prevent it:
- Scan insurance cards - don’t type them
- Verify demographics at every visit, not just new patients
- Use eligibility response data to cross-check what you have on file
- Build data validation into intake forms (DOB format, ID format per payer)
3. Coding errors and modifier issues
What it is: The CPT/HCPCS code doesn’t match the documentation, a required modifier is missing, or the code combination triggers an NCCI edit.
Coding denials are the most expensive to fix because they require real expertise - coders, not front-desk staff. Common patterns:
- Missing modifiers - 25 (separate E/M on day of procedure), 59 (distinct procedural service), GA/GY/GZ for Medicare ABN
- NCCI bundling edits - two codes billed together that payers consider bundled
- Unsupported codes - level 4 E/M billed without the documentation to support it
- Wrong place of service - 11 (office) vs 22 (outpatient hospital) has significant reimbursement implications
Typical denial codes: CO-11 (diagnosis inconsistent with procedure), CO-97 (bundled), CO-4 (procedure code inconsistent with modifier).
How to prevent it:
- Run claims through a scrubbing tool that checks NCCI edits before submission
- Coder review on any claim above a threshold (commonly $500 or new CPTs)
- Documentation templates that prompt for modifier-relevant information
- Track denial codes by provider to catch patterns early
4. Duplicate claim denials
What it is: The payer thinks they’ve already received and processed this claim.
Duplicates happen for legitimate reasons (resubmitting a corrected claim without the right frequency code) and illegitimate ones (accidentally submitting the same claim twice through different channels).
Typical denial codes: CO-18 (duplicate claim/service).
How to prevent it:
- Always use frequency codes (7 = replacement, 8 = void) when resubmitting
- Don’t submit paper and electronic claims for the same service
- Track claim status before resubmitting - the original may still be processing
- If a denial is a true duplicate, pull the original’s status before appealing
5. Prior authorization not obtained
What it is: The service required prior authorization and it wasn’t obtained before the visit.
Prior auth requirements shift constantly, and they’re payer-specific. What’s authorized for Anthem may not be for UHC. Services that didn’t require auth last year may require it this year. Practices that don’t actively maintain a payer-specific auth matrix will get caught.
Typical denial codes: CO-197 (precertification/authorization absent).
How to prevent it:
- Maintain a payer-specific authorization matrix by CPT code
- Check auth requirements during scheduling, not at check-in
- Automate auth submission where possible (increasingly available via EHR integrations)
- Have a backup plan for emergency services - retroactive auth processes vary by payer
The financial cost of a prior auth denial is often the full charge, with limited appeal recourse. Worth investing in prevention.
6. Timely filing
What it is: The claim was submitted after the payer’s filing deadline.
Timely filing windows vary wildly - from 90 days for some Medicaid plans to 365 days for commercial payers. A claim that lands on the wrong side of the deadline is usually dead.
Typical denial codes: CO-29 (time limit for filing has expired).
How to prevent it:
- Know every payer’s timely filing window and track claim age against it
- Submit clean claims within 7 days of service
- Reports that surface claims approaching their filing deadline
- For denied claims being reworked, don’t let them age out - work them within 30 days
Timely filing denials are typically unappealable. This is a preventable category where the cost of failure is 100%.
7. Medical necessity
What it is: The payer determined the service wasn’t medically necessary based on their policy.
Medical necessity denials are the hardest - they require clinical argument, not just data correction. They also have the highest upside on appeal. A strong appeal with chart documentation and literature citations can win a medical necessity denial that would otherwise be written off.
Typical denial codes: CO-50 (non-covered - not deemed medically necessary), CO-167 (diagnosis not covered).
How to prevent it:
- Document medical necessity in the chart at the time of the visit - not retroactively
- Know each payer’s LCD/NCD policies for the services you commonly bill
- Use ICD-10 codes at the highest specificity the documentation supports
- Build appeal templates for the denials you see repeatedly
The pattern behind all seven
Five of these seven (eligibility, demographics, coding, auth, timely filing) are process failures - preventable with better front-end workflow. Two (duplicates, medical necessity) are mostly technical/clinical - preventable with better coding hygiene and documentation discipline.
Every practice has its own mix. The first step is always data: which of these seven is hitting your practice hardest? Once you know, you know where to invest.
Want a denial audit of your own claims? Taiga can analyze your denial patterns and tell you exactly where the leaks are. Book a call.