ICD-10-CM Coding Guidelines 2026: Simplified Summary for Medical Coders

The ICD-10-CM Coding Guidelines 2026 provide the foundation for accurate medical coding, billing, and healthcare reporting. These rules help medical coders, billers, and healthcare professionals assign the most specific and valid diagnosis codes from the ICD-10-CM system. By following the general coding guidelines, coders can ensure compliance with CMS (Centers for Medicare & Medicaid Services) and NCHS (National Center for Health Statistics) standards while reducing claim denials and improving documentation accuracy. In this article, we break down the updated 2026 guidelines into simple, easy-to-understand steps for both beginners and experienced coders.


1. Locating a Code in ICD-10-CM

Always start with the Alphabetic Index to find a possible code, then confirm it in the Tabular List. The Index may not include all required characters, so you must check the Tabular List for details like laterality (left, right, bilateral) and 7th character extensions.

Tip: If you see a dash (-) in the Alphabetic Index, it means more characters are required.


2. Level of Detail in Coding

Codes must be reported to the highest level of specificity.

  • ICD-10-CM codes can have 3–7 characters.

  • A 3-character code can only be used if there’s no more detailed option.

  • If a code requires a 7th character and you don’t add it, the code is invalid.


3. Reportable Diagnosis Codes

Use codes from A00.0–T88.9, Z00–Z99.8, and U00–U85 to capture diagnoses, conditions, or reasons for the patient encounter.


4. Signs and Symptoms

If a definitive diagnosis is not available, you can code signs and symptoms (often from Chapter 18, R00–R99). Once a confirmed diagnosis is documented, symptoms should not be coded separately unless required.


5. Conditions That Are Part of a Disease

Do not code symptoms that are routinely part of a disease unless the classification instructs otherwise.


6. Conditions Not Usually Part of a Disease

If a symptom is not typically associated with a condition, code it separately when documented.


7. Multiple Coding for One Condition

Some conditions require two or more codes:

  • Etiology/manifestation pairs (cause + effect).

  • “Use additional code” notes signal that another code is needed.

  • “Code first” notes mean you must report the underlying cause first.


8. Acute and Chronic Conditions

If both acute (or subacute) and chronic forms of a condition are documented, assign both codes. The acute condition is sequenced first.


9. Combination Codes

A combination code is one code that covers:

  • Two diagnoses, or

  • A diagnosis with a complication/manifestation.

Only use multiple codes if the combination code does not fully describe the condition.


10. Sequela (Late Effects)

A sequela is the long-term effect of a previous illness or injury (e.g., scar after a burn). Coding usually requires two codes:

  1. The condition resulting from the sequela (first).

  2. The sequela code (second).


11. Impending or Threatened Conditions

  • If the condition occurs, code it as confirmed.

  • If it does not occur, look for subentries in the Index under “impending” or “threatened.”

  • If no code exists, code the underlying condition only.


12. Same Code Reported More Than Once

Each ICD-10-CM code can only be reported once per encounter, even if bilateral. Use laterality or additional codes if available.


13. Laterality

Some codes specify right, left, or bilateral.

  • If bilateral is not available, report both right and left codes.

  • If documentation does not specify the side, assign “unspecified.”

  • Coders may use supporting documentation from other clinicians to determine laterality, but conflicts must be clarified with the provider.


14. Documentation by Non-Providers

Certain details (e.g., BMI, ulcer stage, coma scale, NIH Stroke Scale, SDOH, blood alcohol level) may be documented by other clinicians and can be coded. However, the diagnosis itself must come from the provider.


15. Syndromes

Follow Alphabetic Index instructions for syndromes. If no direct code exists, code the documented manifestations.


16. Complications of Care

Assign a complication code only when the provider documents a cause-and-effect relationship between a treatment/procedure and the condition. Not all conditions after surgery are considered complications.


17. Borderline Diagnoses

A borderline diagnosis should be coded as confirmed unless a specific “borderline” entry exists (e.g., borderline diabetes).


18. Signs/Symptoms/Unspecified Codes

Unspecified codes are acceptable when:

  • The provider does not yet know the exact condition.

  • Documentation lacks detail.

  • A definitive diagnosis cannot be made.

⚠️ Avoid overusing unspecified codes—use them only when truly necessary.


19. Hurricane Aftermath Coding

Special rules apply when coding encounters after a hurricane or disaster:

  • Use external cause codes (X37.0-) to indicate hurricane-related injuries.

  • These codes are secondary and explain how the injury happened.

  • If unclear, assume the injury was hurricane-related.

  • Z codes (e.g., Z59.0 Homelessness, Z75.3 Inaccessibility of healthcare) may also apply.


20. Multiple Sites

When two or more sites are involved, use “multiple site” codes if available. If not, code each site individually.


✅ Final Takeaway

Accurate coding requires specificity, documentation review, and attention to conventions like “code first” and “use additional code.” Coders should always confirm codes in the Tabular List and query providers when clarification is needed.


📌 Disclaimer

This article is a simplified summary of the ICD-10-CM Official Guidelines for Coding and Reporting (FY 2026). For the full official text, refer to the CMS guidelines PDF and the CDC/NCHS ICD-10-CM page. Always follow the official guidance when coding for compliance.

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Disclaimer:

The content on this site is for educational purposes only and does not constitute medical, legal, or billing advice. Always verify the latest CPT®, CMS, and payer guidelines before coding or submitting claims. The author and this website assume no responsibility for any loss, liability, or denial resulting from the use of this information.