ICD-10 K35.21
Non-Billable HeaderAcute appendicitis with generalized peritonitis, with abscess
About ICD-10-CM K35.21
ICD-10-CM code K35.21 represents Acute appendicitis with generalized peritonitis, with abscess. This is a non-billable header code in the Digestive System chapter (block K35). The 2026 edition of ICD-10-CM K35.21 became effective on October 1, 2025. Non-billable codes cannot be used as a primary or secondary diagnosis on a claim, use a more specific child code instead.
Medicare LCD Coverage for K35.21
Local Coverage Determinations (LCDs) from CMS MACs that list K35.21 as a covered diagnosis.
This doesn't mean the code isn't covered, it means no MAC has issued a Local Coverage Determination naming this specific code. Coverage may still apply under National Coverage Determinations or general medical-necessity rules.
Commercial Payer Coverage
Coverage policies from major commercial payers referencing K35.21.
Our payer policy database covers Aetna, Cigna, Anthem, BCBS, Humana, and Medicare Advantage plans, but K35.21 doesn't currently appear in any indexed policy. The code may still be covered under standard plan benefits.
CPT Codes Commonly Billed with K35.21
Procedures frequently paired with this diagnosis based on PayerReady's Dx↔Px linkage data.
Codes Adjacent To K35.21
Other codes in section K35-K38 (Diseases of appendix).
ICD-10 K35.21, Billing FAQ
Is ICD-10 code K35.21 billable? +
No, K35.21 is a non-billable header code. Use a more specific child code from block K35 when submitting claims.
What CPT codes are commonly billed with K35.21? +
Procedures frequently paired with K35.21 include: 44970, 44950.
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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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