ICD-10-CM
The Clinical Modification of the WHO ICD-10 code set used in the United States to report diagnoses.
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
ICD-10-CM is maintained by NCHS and CMS. The HIPAA-mandated diagnosis code set for outpatient claims. Updates take effect every October 1.
How it shows up in your practice
Every claim needs at least one ICD-10-CM code linked to each CPT line. Specificity matters: unspecified codes are a common denial reason. Train coders on the annual updates before they take effect.
Sources
- WHO / CDC — ICD-10-CMhttps://www.cdc.gov/nchs/icd/icd-10-cm.htm
- CMS — ICD-10 Resourceshttps://www.cms.gov/medicare/coding-billing/icd-10-codes
Look up ICD-10 codes in Ask D3
Open ask d3 →Related terms
- BillingCPT (Current Procedural Terminology)The AMA-maintained code set that describes medical, surgical, and diagnostic services for billing.
- CodingICD-10-PCSThe Procedural Coding System used in the United States to report inpatient hospital procedures.
- DocumentationUnspecified Diagnosis CodeAn ICD-10-CM code ending in characters that signal the documentation lacked the specificity for a more precise code.
- CodingMedical NecessityThe 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.
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
- GlossaryICD-10-PCSThe Procedural Coding System used in the United States to report inpatient hospital procedures.
- GlossaryUnspecified Diagnosis CodeAn ICD-10-CM code ending in characters that signal the documentation lacked the specificity for a more precise code.
- GlossaryMedical NecessityThe 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.
- GlossaryCPT (Current Procedural Terminology)The AMA-maintained code set that describes medical, surgical, and diagnostic services for billing.
- GlossaryICD-10-CM Z CodeICD-10-CM categories Z00-Z99 used to document encounters for reasons other than disease or injury, including screenings, follow-up, social determinants, and personal/family history.
- GlossaryDocumentation SpecificityThe level of detail in clinical documentation needed to support the diagnosis and service codes reported.
- 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.
- BillingThe ICD-10 Codes That Get Primary Care Claims Denied (and How to Pick the Right One)I10 vs I11, E11.9 vs E11.40, Z00.00 vs Z00.01. The diagnosis coding mistakes that cause denials and how to fix them.
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.