ICD-10, ICD-10-CM, and ICD-10-PCS
The World Health Organization publishes ICD. The United States uses a clinical modification for diagnoses (ICD-10-CM) and a separate procedure system for inpatient hospital procedures (ICD-10-PCS). Professional and most outpatient procedure coding uses CPT and HCPCS instead of ICD-10-PCS.
- ICD-10-CM: diagnoses (why the patient was treated)
- ICD-10-PCS: inpatient facility procedures
- CPT / HCPCS: professional and many outpatient procedures and supplies
Why “what is ICD-10” still trends every year
The US switched from ICD-9-CM to ICD-10-CM/PCS in 2015, but new hires, vendors, and patients still search the term. Annual CMS updates also refresh search interest. If you need current codes, use the CMS ICD-10 page for the fiscal year in force—not a blog screenshot.
How many characters?
ICD-10-CM codes are 3–7 characters. Specificity (laterality, encounter type, trimester) often lives in the later characters. Unspecified codes exist when the record cannot support more detail.
Who should assign the code?
Clinicians document; trained coders (or software plus a coder) assign ICD-10-CM using the official guidelines, including coding conventions and chapter-specific rules.
Where automation fits
AI can propose ICD-10-CM from notes. It cannot rewrite CMS guidelines. See HealthCoder ICD-10 automation if you want the product path after you understand the standard. For inpatient procedure codes, read ICD-10-CM vs ICD-10-PCS so you do not treat clinic automation as a PCS encoder.
Frequently asked questions
Is ICD-10 the same as CPT?+
No. ICD-10-CM is diagnoses. CPT is procedures and services (AMA). See our ICD-10 vs CPT article.
Where do I download official ICD-10-CM files?+
From CMS (coding-billing ICD-10 pages) and CDC/NCHS ICD-10-CM resources linked in the citations below.