Most denied claims are never worked at all
The uncomfortable arithmetic of small-practice billing: a denied claim is worth perhaps a hundred dollars and takes twenty minutes to work, so it does not get worked. Multiply by a caseload and a year, and the amount quietly written off exceeds what most practices would notice losing in any other form.
Before anything else, a distinction that determines where to look.
Rejection versus denial
A rejection happens before adjudication. The clearinghouse or the payer's intake system refuses the claim for a format or data problem — a malformed identifier, a missing field, an invalid code — and it never becomes a claim. There is no appeal, because nothing was decided. You correct and resubmit.
A denial happens after adjudication. The payer processed the claim and decided not to pay it, or to pay less. This appears on the ERA with an adjustment code, and it is appealable.
The practical importance: rejections sit in the clearinghouse, denials sit in the ERA, and a practice watching only one of those places is missing a category of lost revenue entirely. Rejections are the more commonly missed, because they never reach the payer and so never appear in payer-side reporting.
The denial categories worth process
Eligibility and coverage
Coverage terminated, wrong plan, another payer primary. Usually preventable by verification before the session, and usually recoverable by submitting to the correct payer if timely filing allows.
Authorisation
CO-197 and relatives. Sometimes recoverable through retroactive authorisation; often
not. This is the category where prevention dominates recovery — see
prior authorisation.
Coding
Invalid code combinations, bundling, missing modifiers, diagnosis pointers that do not support the service. Generally correctable and resubmittable, and generally worth analysing in aggregate rather than one at a time, because coding denials cluster around a specific habit.
Medical necessity
CO-50. The most serious category and the one requiring actual documentation to
appeal. If the note does not evidence a medically necessary service, the appeal will fail — which
means this denial is really a documentation problem surfacing as a billing one. See
the golden thread.
Timely filing
CO-29. Almost always terminal. Covered below.
Duplicate
Frequently a false positive — a resubmission read as a duplicate, or two legitimate same-day services such as an evaluation and a therapy session. Usually resolvable with a corrected claim indicator or documentation of the distinct services.
Timely filing
The deadline that ends the conversation. Filing windows commonly run from 90 days to a year from date of service, vary by payer and contract, and are enforced strictly.
Two deadlines, not one. The window for the original claim is separate from the window for an appeal, and the appeal window typically runs from the date of the denial rather than the date of service. A denial arriving on day 300 of a 365-day filing window may carry a 60-day appeal deadline that expires well after the original window has closed — and that appeal deadline is the one that matters.
Where a claim was filed on time and denied for timely filing anyway, proof of timely submission — a clearinghouse acknowledgement with a date — usually resolves it. This is a specific and common reason to retain clearinghouse acceptance reports rather than only the claims themselves.
Appeals
Levels vary by payer and plan type, but the shape is consistent: an internal first-level appeal, sometimes a second internal level, and for many plans an external independent review after internal options are exhausted. Self-funded employer plans and Medicare Advantage have their own structures.
A first-level appeal that works contains four things and little else: what was denied and why, why the denial is incorrect, the specific documentation supporting that, and what you are asking for. Long appeals restating clinical narrative fare worse than short ones addressing the stated reason directly.
Attach the relevant documentation rather than the entire chart. A reviewer with twelve pages will read them; a reviewer with a hundred will skim.
Building a process that survives a busy month
Denial management fails in solo and small group practice for a structural reason: it is nobody's job, and it is always less urgent than a client in the room.
What makes it survivable is reducing per-denial cost rather than increasing discipline. Route denials into a queue automatically rather than requiring someone to find them. Group them by reason so one fix addresses several claims. Handle the categories with a standard response as a batch. And know your own numbers — a practice that cannot say what percentage of claims denied last quarter, and for what reasons, is not in a position to decide whether the problem is worth solving.
When to write it off
A legitimate decision, made deliberately. Some denials cost more to work than they return, and some are genuinely unrecoverable. What matters is that the write-off is a decision with a reason recorded, not a claim that quietly aged out — because the second kind never produces the aggregate picture that would tell you to fix the cause.
The denial rate worth knowing
One number is worth tracking above the others: the proportion of claims denied on first submission. It is the single best indicator of whether your front-end process — verification, coding, authorisation tracking — is working, because every first-pass denial is a claim that could have been prevented rather than recovered.
Track it by payer as well as overall. A practice with an acceptable aggregate rate frequently has one payer driving most of the problem, and that is a solvable, specific conversation rather than a general resolution to be more careful.
Corrected claims versus appeals
A distinction that determines which route to take, and taking the wrong one wastes the deadline.
A corrected claim is appropriate where the original contained an error — wrong code, wrong modifier, wrong diagnosis pointer, wrong units. You resubmit with a correction indicator referencing the original claim number. Submitting a corrected claim without that reference produces a duplicate denial rather than a correction.
An appeal is appropriate where the claim was correct and the payer's decision was wrong — medical necessity denials, incorrect application of benefits, misapplied bundling rules. Appeals argue; corrected claims fix.
Sending an appeal where a correction was needed usually produces an upheld denial, because the reviewer is being asked to approve a claim that is genuinely wrong. Sending a correction where an appeal was needed resets nothing, because the claim was already right.
Who does this work
Worth being concrete, because the honest answer shapes everything else. In solo practice it is you, which means the process must be cheap enough to survive a full caseload. In small group practice it is usually an administrator whose time is also spent on scheduling and intake, which means denials lose to anything with a person waiting.
Outsourced billing changes the economics but not the accountability: a billing service works the denials it is incentivised to work, and low-value claims are frequently not among them. Whoever does it, someone should be able to state the first-pass denial rate from memory — if nobody can, the work is not happening regardless of who was assigned it.
Verified 29 July 2026. Transaction standards (X12 270/271, 835, 837) are set federally under HIPAA; coverage, authorisation requirements, timely-filing windows and appeal rights are set by individual payers and by state law, and vary by contract. Figures described as typical are illustrative, not guarantees. Primary references: CMS billing guidance; X12 code lists; HHS HIPAA. This page is billing reference, not legal or coding advice.