Medicare Part B Letter of Medical Necessity Guide
How to write an LMN and overturn a prior authorization denial with Medicare Part B. Includes denial reasons, turnaround times, appeals address, and clinician tips.
Quick Facts
- Avg Turnaround: 60 days redetermination
- Appeals Address: MAC appeals (varies by jurisdiction)
- Provider Portal: https://www.cms.gov/
Why Medicare B Denies Prior Authorizations
- 1. Not reasonable and necessary per LCD
- 2. Missing ICD-10 support
- 3. Site of care (hospital outpatient vs. office)
Clinician Tips for Medicare B
- ✓ Reference the applicable LCD or NCD by number
- ✓ Include ASP+6% pricing awareness
- ✓ J-code billing with proper modifiers
Part B covers provider-administered drugs; LCDs govern medical necessity.
Medicare B Prior Authorization FAQ
Why does Medicare B deny prior authorizations?
The most common Medicare B denial reasons are: Not reasonable and necessary per LCD; Missing ICD-10 support; Site of care (hospital outpatient vs. office).
How long does Medicare B take to review a prior authorization?
Medicare B typically responds in 60 days redetermination.
What should a Letter of Medical Necessity for Medicare B include?
An LMN for Medicare Part B should reference the specific medical policy or coverage bulletin, document failed first-line therapies with dates, include current labs and ICD-10 codes, and cite supporting clinical guidelines. Part B covers provider-administered drugs; LCDs govern medical necessity.