ICD-10 K35.80
Billable / Specific CCUnspecified acute appendicitis
About ICD-10-CM K35.80
ICD-10-CM code K35.80 represents Unspecified acute appendicitis. This is a billable/specific code in the Digestive System chapter (block K35). The 2026 edition of ICD-10-CM K35.80 became effective on October 1, 2025.
Coding Tips for K35.80
Specialist guidance from the PayerReady Medical Coding Team. Specificity warnings, HCC capture rules, sequencing notes.
K35.80 is designated CC for MS-DRG grouping. On inpatient claims, this code can shift the DRG to the with-CC variant when documented as a present-on-admission secondary diagnosis. Hospital CDI programs flag CC opportunities during chart review. Failure to capture this code may leave 30 to 80 percent of the inpatient stay revenue unrealized.
Inclusion Terms / Approximate Synonyms
Clinical terms and conditions classified under K35.80. Per CMS ICD-10-CM Tabular 2026.
- Acute appendicitis NOS
- Acute appendicitis without (localized) (generalized) peritonitis
Inpatient DRG Impact, CC
codes Unspecified acute appendicitis. As a Complication/Comorbidity (CC), this contributes to DRG severity adjustment when documented alongside the principal diagnosis.
Medicare LCD Coverage for K35.80
Local Coverage Determinations (LCDs) from CMS MACs that list K35.80 as a covered diagnosis.
Showing top 10 of 107 total . Click a CPT for full coverage scope.
Commercial Payer Coverage
Coverage policies from major commercial payers referencing K35.80.
3 Medicare
CPT Codes Commonly Billed with K35.80
Procedures frequently paired with this diagnosis based on PayerReady's Dx↔Px linkage data.
Convert K35.80 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 |
|---|---|---|
| K35.80 | 5409 | 10000 |
Flags format (5 digits): Approximate · No Map · Combination · Scenario · Choice List. Source: CMS 2017 GEMs (final version).
Codes Adjacent To K35.80
Other codes in section K35-K38 (Diseases of appendix).
ICD-10 K35.80, Billing FAQ
Is ICD-10 code K35.80 billable? +
Yes, K35.80 is a billable ICD-10-CM code that can appear as a primary or secondary diagnosis on claims.
What other names or terms map to K35.80? +
ICD-10 K35.80 includes: Acute appendicitis NOS; Acute appendicitis without (localized) (generalized) peritonitis.
Is K35.80 a CC or MCC for inpatient DRG? +
Yes, this code is designated as CC. Documenting as a secondary diagnosis on inpatient claims can shift the DRG to a higher-weighted category.
What CPT codes are commonly billed with K35.80? +
Procedures frequently paired with K35.80 include: 44970, 44950.
What ICD-9 codes does K35.80 map to? +
Per CMS GEMs, K35.80 maps to ICD-9 codes: 5409. 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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