A denial letter is a short document that does three jobs at once. It names a reason, cites the clause the payer is relying on, and starts a clock. Most appeals that fail do so because the person working the account answered the reason and never looked at the other two. The reason is the part written for humans. The clause and the deadline are the parts that decide where the file goes next and how long you have to get it there.
Work from the letter, not from memory of what that payer usually does. Two denials with identical summary language can sit in different categories, carry different appeal rights, and run on clocks that differ by weeks.
Sort the denial by category before you write a word
There are really three families, and they do not share a playbook.
The first is clinical: the payer agrees the service happened and says it was not covered at that level of care, or not supported as inpatient, or not reasonable and necessary. The second is technical or administrative: missing authorization, untimely filing, eligibility, no referral on file, coordination of benefits. The third is coding and documentation: a DRG downgrade, an unbundling edit, a modifier the payer did not accept.
Only the first family needs a physician's signature on the argument. The second family is usually won or lost with a fax confirmation, a call log, or an eligibility screenshot, and a clinical narrative adds nothing. The third sits with coding, and the appeal is a reading of the record against the guideline the payer cited.
Sorting takes two minutes and saves days. A hospital that routes every denial to the same queue will put physician review hours into timely-filing letters, which is the most expensive way to lose.
What changed, and why it matters to the clinical pile
The ground under medical-necessity denials shifted in 2024. Medicare Advantage plans are now required to apply Medicare coverage criteria when making medical necessity determinations for basic benefits, rather than substituting proprietary screening tools that are more restrictive than the underlying Medicare rules. Where Medicare has a rule, the plan has to follow it. Where internal criteria are used to fill a gap, the plan is expected to disclose them. The Centers for Medicare & Medicaid Services oversees those plan obligations.
The practical effect is that the inpatient admission benchmark, built around the expectation of a stay spanning two midnights, is no longer something a plan can screen past with a commercial criteria set. A denial that says the case failed inpatient criteria, and names only a vendor product as the authority, is now answerable on its face. You are no longer arguing clinical judgment against clinical judgment. You are pointing at the rule the plan is required to apply.
Prior authorization timelines tightened in the same period, with standard and expedited decision windows and a requirement that denials give a specific reason. That second part is the one to use. A denial that does not identify the criteria it applied is a denial you can ask to be reissued, and the request itself is worth making in writing.
The order, and the clocks that control it
Route in this sequence, and do not skip forward because a later level feels more serious.
- Concurrent, before discharge. If the patient is still in the building and the issue is status, this is the cheapest hour you will ever spend. A peer-to-peer conversation held before discharge can resolve a case that would otherwise take six months of letters.
- Peer-to-peer, inside the window. Most plans allow a limited period after the adverse determination, often measured in days, and some allow only one attempt. Confirm the window in the letter rather than assuming it matches the last payer you dealt with.
- First-level appeal or reconsideration. Written, with the record attached and the specific clause quoted back. For traditional Medicare this is redetermination with the contractor; for Medicare Advantage it is plan reconsideration, which moves automatically to an independent review entity when the plan upholds itself.
- Second level and external review. Independent review, a qualified independent contractor, or a state external review organization depending on the product. Commercial plans vary, and the letter names the entity.
- Administrative law judge and beyond. Slow, document-heavy, and worth it only above an amount-in-controversy threshold that the plan or the program will state.
Write the deadline for every level on the account the day the denial is logged. Filing late forfeits an appeal that would have won on the merits, and no payer is required to tell you twice.
Who writes the clinical argument, and how to build the judgment to pick cases
A medical-necessity appeal written by a nurse reviewer and signed by nobody reads as an opinion. The same facts, set out by a physician who addresses the plan's stated criteria point by point, reads as a rebuttal. That is the gap organizations fill with internal physician advisors or with outsourced physician advisory services, which handle status determinations, peer-to-peer calls, and written appeals at volumes that are hard to staff for in-house.
Judgment comes from tracking outcomes, not from instinct. Keep a simple log with five fields: payer, denial reason code, level reached, outcome, and dollars. After a quarter you will see patterns that no vendor report will give you. One plan overturns status denials at peer-to-peer and almost never at written appeal, so the call is the whole game. Another never moves until external review, which means the first two levels are paperwork you file to preserve rights rather than contests you expect to win.
That log is also what tells you when to stop. A DRG downgrade worth a few hundred dollars, against a payer that has upheld eleven of the last twelve, is a case to close. Appeal capacity is finite, and spending it where the history says you win is the entire discipline.
Quote the clause, attach the proof
The strongest appeal letters are short. They name the determination and its date, quote the exact sentence the payer relied on, and then answer that sentence with the record: the physician's documented expectation of the length of stay, the orders, the times, the applicable coverage rule. Attach the pages and cite them by number. A reviewer with a queue will read a letter that tells them where to look.
The rules that changed in 2024 gave hospitals something they did not reliably have before, which is a fixed standard to point at when a plan applies its own. Read the letter for which standard it used, and the appeal largely writes itself.