ICD-10 C31.9
Billable / Specific HCC v28: 11Malignant neoplasm of accessory sinus, unspecified
About ICD-10-CM C31.9
ICD-10-CM code C31.9 represents Malignant neoplasm of accessory sinus, unspecified. This is a billable/specific code in the Neoplasms chapter (block C31). The 2026 edition of ICD-10-CM C31.9 became effective on October 1, 2025.
Coding Tips for C31.9
Specialist guidance from the PayerReady Medical Coding Team. Specificity warnings, HCC capture rules, sequencing notes.
C31.9 is a CMS-HCC v28 risk-adjustment code (category 11). To count for the patient Risk Adjustment Factor (RAF), document the diagnosis with MEAT language each calendar year: Monitored, Evaluated, Assessed, Treated. A diagnosis on the problem list alone does not satisfy CMS RADV audit standards. Include the diagnosis in the assessment with current status and current treatment plan.
Medicare Advantage HCC Impact
Capture this diagnosis annually for accurate risk adjustment. Missed HCC captures are the #1 revenue leak in Medicare Advantage risk programs.
Medicare LCD Coverage for C31.9
Local Coverage Determinations (LCDs) from CMS MACs that list C31.9 as a covered diagnosis.
Showing top 10 of 545 total . Click a CPT for full coverage scope.
Commercial Payer Coverage
Coverage policies from major commercial payers referencing C31.9.
1 Cigna
5 Medicare
CPT Codes Commonly Billed with C31.9
Procedures frequently paired with this diagnosis based on PayerReady's Dx↔Px linkage data.
- 81540 CMS LCD: Billing and Coding: MolDX: bioTheranostics Cancer TYPE ID� Update CMS LCD
Convert C31.9 to ICD-9-CM
Per CMS General Equivalence Mappings (GEMs), useful for legacy data review and historical claim analysis.
| ICD-10 | ICD-9 | Mapping Flags |
|---|---|---|
| C31.9 | 1609 | 00000 |
Flags format (5 digits): Approximate · No Map · Combination · Scenario · Choice List. Source: CMS 2017 GEMs (final version).
Codes Adjacent To C31.9
Other codes in section C30-C39 (Malignant neoplasms of respiratory and intrathoracic organs).
ICD-10 C31.9, Billing FAQ
Is ICD-10 code C31.9 billable? +
Yes, C31.9 is a billable ICD-10-CM code that can appear as a primary or secondary diagnosis on claims.
Does C31.9 affect Medicare Advantage HCC risk adjustment? +
Yes. C31.9 maps to CMS-HCC v28 category 11. Capture this diagnosis annually for accurate Medicare Advantage risk score.
What CPT codes are commonly billed with C31.9? +
Procedures frequently paired with C31.9 include: 81540.
What ICD-9 codes does C31.9 map to? +
Per CMS GEMs, C31.9 maps to ICD-9 codes: 1609. Useful for legacy data review and historical claim analysis.
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Reviewed by the PayerReady Medical Coding Team
Verified against the CMS 2026 code set on May 31, 2026.
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