Appealing a Medicare CO-50 Denial
A Medicare CO-50 denial (not medically necessary) is one of the most common claim rejections behavioral health therapists face. This guide explains exactly what caused the denial and the most effective appeal strategy for behavioral health practices.
What this denial means
The payer is saying the service was not medically necessary under their criteria. In behavioral health, this denial is particularly common and often reflects internal coverage policies that are more restrictive than what MHPAEA permits.
Your appeal strategy
Medicare is not subject to the federal MHPAEA mental health parity requirement, so do not raise a parity argument on this claim. Support the appeal with the treating clinician's clinical documentation and base your argument on Medicare's own coverage criteria and appeal process (see "What Medicare requires" below).
What Medicare requires
60 calendar days (Level-1 appeal)
180 days from Level-1 denial
Traditional Medicare (Parts A/B) follows the five-level appeals process: Redetermination → Reconsideration (QIC) → ALJ → Medicare Appeals Council → Federal Court. Medicare Advantage (Part C) provides an analogous five-level process under 42 CFR § 422.560 et seq. Federal MHPAEA does NOT apply to Medicare; do not raise a 29 CFR § 2590.712 parity argument on a Medicare or Medicare Advantage denial. Base the appeal on Medicare coverage criteria and the applicable LCD/NCD.
Generate your Medicare CO-50 appeal letter
Therapists get 5 free letters every month. Appealing your own denial? It's $19 per letter, one-time, no subscription. No credit card needed to start.
Generate my appeal letter →Frequently asked questions
How long does Medicare have to respond to a CO-50 appeal?
Under federal regulations, Medicare must respond to a Level-1 internal appeal within 60 calendar days. State insurance law, including your state's prompt-payment statute, does not apply to this federal program — confirm the current response-window rules directly with the program administrator before filing. If you receive an adverse determination, you typically have 180 calendar days from the date of the Level-1 denial to request external review. Send the appeal via certified mail or through the payer's portal and keep documentation of the submission date.
Does MHPAEA apply to CO-50 denials?
No. The federal Mental Health Parity and Addiction Equity Act (MHPAEA) does not apply to Medicare. Medicare is governed by separate program rules rather than the federal MHPAEA standard (29 CFR § 2590.712). Base your appeal on the program's own coverage rules and appeal process — do not demand a 29 CFR § 2590.712 NQTL comparative analysis from this program. Traditional Medicare (Parts A/B) follows the five-level appeals process: Redetermination → Reconsideration (QIC) → ALJ → Medicare Appeals Council → Federal Court. Medicare Advantage (Part C) provides an analogous five-level process under 42 CFR § 422.560 et seq. Federal MHPAEA does NOT apply to Medicare; do not raise a 29 CFR § 2590.712 parity argument on a Medicare or Medicare Advantage denial. Base the appeal on Medicare coverage criteria and the applicable LCD/NCD.
Can I appeal a CO-50 denial more than once?
Yes. Most payers, including Medicare, allow at least two levels of internal appeal (Level-1 and Level-2 or "expedited" review). Keep copies of every appeal, submission confirmation, and payer response. After exhausting the plan's internal reconsideration, Medicare Advantage appeals follow the federal ladder under 42 CFR Part 422 Subpart M: plan reconsideration → independent review entity → Administrative Law Judge (ALJ) → Medicare Appeals Council → federal court. Traditional Medicare appeals follow 42 CFR Part 405 Subpart I. Your state insurance commissioner has no authority over Medicare appeals.
What documentation do I need to appeal a CO-50 denial from Medicare?
At minimum: the original Explanation of Benefits (EOB) or Remittance Advice (RA) showing the CO-50 denial, the original claim details (CPT code, date of service, NPI, charge amount), and any clinical documentation supporting medical necessity. Submit everything in one packet with a cover letter citing the specific denial code, the date of service, and the claim number.