MLN: Medical Necessity — Local Coverage Determinations (LCDs) and National Coverage Determinations (NCDs)
Reference to Medicare's coverage determinations: NCDs are issued by CMS; LCDs are issued by MACs; both define when an item or service is reasonable and necessary.
Primary source
CMS Medicare Coverage Determination Process →https://www.cms.gov/medicare/coverage/determination-process
Verified May 23, 2026 · This is the authoritative regulator URL. The summary below is a research aid; the linked source controls.
Additional sources
Medicare coverage of an item or service is determined by whether it is "reasonable and necessary for the diagnosis or treatment of illness or injury" (42 USC 1395y(a)(1)(A)). Two formal mechanisms refine the standard for specific items and services.
National Coverage Determinations (NCDs): issued by CMS, apply nationally, and are binding on all MACs. NCDs typically cover technologies with broad cost or clinical impact (e.g., implantable defibrillators, screening colonoscopy, specific lab tests).
Local Coverage Determinations (LCDs): issued by MACs, apply only within the MAC's jurisdiction, and address items and services not covered by an NCD. LCDs specify the clinical conditions under which the service is considered reasonable and necessary, the diagnoses (ICD-10-CM codes) that support coverage, and frequency/utilization limitations.
The Medicare Coverage Database is the search tool for both NCDs and LCDs. Practices billing high-volume Medicare services should reconcile their utilization patterns against current LCDs in their MAC jurisdiction — particularly diagnosis-code support — to reduce post-payment audit exposure.
LCDs are subject to a Reconsideration Process that allows stakeholders to request modification with new evidence; revisions are published with public-comment periods.
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Last reviewed May 23, 2026 · Citation verified May 23, 2026
Research aid, not legal advice. This summary is an administrative research aid prepared by D3rx. It does not certify compliance, provide legal advice, replace counsel, or guarantee an audit outcome. For authoritative regulatory text follow the primary source link at the top of this page. The practice remains responsible for reviewing, adopting, and maintaining its compliance program.