ICD-10 Guidelines Every Coder Must Follow
ICD-10-CM coding isn’t just about picking the “closest” diagnosis — it requires applying strict rules issued by the CDC and CMS to ensure accuracy, consistency, and compliance. Below are the essential ICD-10 guidelines every coder must master.
1. Follow the Official Guidelines FIRST
Before using any code, coders must follow:
Official ICD-10-CM Guidelines for Coding and Reporting
Alphabetic Index → Tabular List sequence
Notes, conventions, and instructional symbols in the Tabular List
You must confirm all codes in the Tabular List, even if found in the Alphabetic Index.
2. Code to the Highest Level of Specificity
ICD-10 uses characters A through Z and numbers to encode detailed information.
Select the most specific code available.
Never truncate a code; always use the full number of characters needed (3–7).
Use additional characters for laterality, severity, trimester, encounter type, etc.
3. Use Combination Codes When Available
Some diagnoses require only one combination code to describe:
The condition and its manifestations
Two diagnoses commonly seen together
A diagnosis with a complication
Example: Type 2 diabetes with kidney complications → one combination code, not two separate codes.
4. Follow “Code First” and “Use Additional Code” Instructions
These sequencing rules are critical.
Code First
– Used for etiology/manifestation pairs
– The underlying condition is coded first
Use Additional Code
– Add codes for manifestations, external causes, or substance use
– These appear after the primary code
Not following these rules leads to incorrect sequencing and claim denials.
5. Understand Excludes Notes (Excludes1 vs Excludes2)
Excludes1 — “NOT coded here”
Two conditions cannot be coded together.
They are mutually exclusive.
Excludes2 — “Not included here”
Indicates separate conditions.
Both codes may be used together if clinically appropriate.
6. Assign Signs & Symptoms Only When No Definitive Diagnosis Exists
When a provider documents unclear findings (e.g., fatigue, fever), assign signs/symptoms only if:
No confirmed diagnosis is established
The symptoms are clinically relevant
If a confirmed diagnosis explains the symptoms, do not code the symptoms separately.
7. Use “History,” “Status,” and “Screening” Codes Correctly
History codes (Z80–Z87) → personal or family history
Status codes (Z91–Z99) → devices or conditions influencing care
Screening codes (Z11–Z13) → when a patient is not presenting with symptoms
These Z codes affect risk adjustment and reimbursement.
8. Follow Laterality Requirements
Many ICD-10 codes require specification of:
Right
Left
Bilateral
Leaving out laterality = coding error.
9. Identify Episode of Care (A, D, S) When Needed
For injuries and some other chapters:
A = Initial encounter (active treatment)
D = Subsequent encounter (routine healing)
S = Sequela (late effects, such as residual pain)
The "S" code requires adding a sequela code after the original injury code.
10. Never Assign Codes Based on Assumptions
Coders must use:
Provider documentation
Coding guidelines
Official definitions
Do NOT infer:
“Probable,” “suspected,” “likely,” or “rule out” diagnoses → Outpatient: code signs/symptoms
“With” → only apply combination rules when the Tabular List indicates association
11. External Cause Codes When Required
External cause codes (V00–Y99) describe:
How an injury happened
Where it occurred
The patient’s activity
Intent (accidental, assault, etc.)
Not always required, but when mandated (e.g., trauma registries), they must be used in the correct sequence.
12. Verify Updates Every October 1
ICD-10-CM updates annually:
New codes
Deleted codes
Revised instructional notes
Updated guidelines
Coders must review changes BEFORE applying codes.
Quick Summary for Coders
✔ Always verify in the Tabular List
✔ Follow “code first,” “use additional code,” “includes,” and “excludes” notes
✔ Use the most specific, complete code
✔ Do not code uncertain diagnoses (outpatient)
✔ Code only what the provider documents
✔ Apply combination codes and laterality correctly
✔ Use Z-codes appropriately
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