Medical Necessity
The standard requiring that services be reasonable and necessary for the diagnosis or treatment of illness or injury or to improve the functioning of a malformed body member.
1 min read · Last reviewed May 23, 2026
At a glance
- Category
- Coding
- Primary sources
- 2
- Workspace handoff
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Where this comes up
Coders meet this term inside the chart at the moment of code selection — picking the E/M level, attaching the right modifier, defending the procedure code against an NCCI edit, or answering an auditor who pulled the encounter for a payer-initiated review.
Full definition
What it is in practice
Section 1862(a)(1)(A) of the Social Security Act sets the Medicare medical-necessity standard. LCDs and NCDs operationalize it for specific services.
How it shows up in your practice
Match ICD-10 diagnoses to the covered indications in the applicable LCD/NCD. Documentation that explains the clinical reasoning is the strongest defense in a post-payment audit.
Sources
- CMS — Local Coverage Determinations (Medicare Coverage Database)https://www.cms.gov/medicare-coverage-database/
- CMS — National Coverage Determinationshttps://www.cms.gov/medicare/coverage/determination-process
Check medical-necessity criteria in Ask D3
Open ask d3 →Related terms
- PayerLCD (Local Coverage Determination)A MAC-published decision about whether a service is reasonable and necessary in its jurisdiction.
- PayerNCD (National Coverage Determination)A CMS-issued nationwide determination of whether Medicare will cover a particular service.
- DocumentationDocumentation SpecificityThe level of detail in clinical documentation needed to support the diagnosis and service codes reported.
- CodingICD-10-CMThe Clinical Modification of the WHO ICD-10 code set used in the United States to report diagnoses.
D3rx is a healthcare-billing and compliance research aid maintained by D3rx Inc. Articles are drafted by an LLM (Anthropic Claude) against primary HHS, OCR, CMS, eCFR, NIST, and state-regulator publications, and reviewed for restraint and source fidelity by the D3rx team.
Reviewer status: a named credentialed reviewer (CHC, CHPC, or healthcare attorney) is being engaged. Until that engagement is finalized, this page does not claim credentialed review.
Related across the archive
- GlossaryLCD (Local Coverage Determination)A MAC-published decision about whether a service is reasonable and necessary in its jurisdiction.
- GlossaryNCD (National Coverage Determination)A CMS-issued nationwide determination of whether Medicare will cover a particular service.
- GlossaryICD-10-CMThe Clinical Modification of the WHO ICD-10 code set used in the United States to report diagnoses.
- GlossaryDocumentation SpecificityThe level of detail in clinical documentation needed to support the diagnosis and service codes reported.
- ComplianceMedicare TPE Audit: The 45-Day Response WindowReceived a Medicare TPE letter from your MAC? You have 45 days from the ADR per claim. Sequence the response, address probe errors, and avoid Round 2.
- RegulationMLN: 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.
- ComplianceRAC Audit Response: First 14 Days After the LetterA Recovery Audit Contractor (RAC) letter starts a 45-day documentation clock and a 30-day discussion-request window (separate from the 120-day Redetermination appeal clock). Sequence the first 14 days correctly.
- Billing99214 vs 99215: When to Bill Each CodeLearn the difference between 99214 and 99215: when each applies, what documentation you need, and the $40/visit revenue impact.
This glossary entry is a research aid for billing and compliance staff. It does not provide legal, medical, or financial advice and does not replace counsel. References cited link to primary sources at HHS, OCR, CMS, eCFR, NIST, and the relevant payer or industry body.