2027 ICD-10-CM Diagnosis Code K35.80Unspecified acute appendicitis
ICD-10-CM Codes›K00–K95›K35-K38›K35
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Not Chronic
K35.80 is a billable ICD-10-CM diagnosis code for unspecified acute appendicitis. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 393 through 395. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 24 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Appendicitis and other appendiceal conditions.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Abscess of appendix
- Acute appendicitis
- Acute appendicitis with appendix abscess
- Acute appendicitis without peritonitis
- Acute fulminating appendicitis
- Acute gangrenous appendicitis
- Acute obstructive appendicitis
- Acute phlegmonous appendicitis
- Acute suppurative appendicitis
- Complicated appendicitis
- Gangrenous appendicitis
- Large bowel gangrene
- Purulent enteritis
- Suppurative appendicitis
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to K35.80: its own notes plus those printed at Chapter 11. A note printed at a category, block or chapter applies to every code under it.
Applicable To
Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.
- Acute appendicitis NOS
- Acute appendicitis without (localized) (generalized) peritonitis
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
- certain conditions originating in the perinatal period (P04-P96)
- certain infectious and parasitic diseases (A00-B99)
- complications of pregnancy, childbirth and the puerperium (O00-O9A)
- congenital malformations, deformations and chromosomal abnormalities (Q00-Q99)
- endocrine, nutritional and metabolic diseases (E00-E88)
- injury, poisoning and certain other consequences of external causes (S00-T88)
- neoplasms (C00-D49)
- symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name K35.80, its category, or a range that includes it.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
Gangrene, gangrenous (connective tissue) (dropsical) (dry) (moist) (skin) (ulcer) See Also: Necrosis; I96
appendix K35.80
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Appendicitis
acute inflammation of the vermiform appendix.
Patient EducationClinical
Appendicitis
The appendix is a small, tube-like organ attached to the first part of the large intestine. It is located in the lower right part of the abdomen. It has no known function. A blockage inside of the appendix causes appendicitis. The blockage leads to increased pressure, problems with blood flow, and inflammation.
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert K35.80 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About K35.80Overview
What is the ICD-10 code for unspecified acute appendicitis?
The ICD-10-CM code for unspecified acute appendicitis is K35.80 (sometimes written as K3580). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is K35.80 (Other and unspecified acute appendicitis) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report unspecified acute appendicitis on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does K35.80 group to?
When unspecified acute appendicitis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 394, 395, 393, with relative weights from 0.6379 to 1.5877 depending on complications. Higher weights mean higher Medicare reimbursement.
Is K35.80 a CC or MCC?
CMS lists K35.80 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 24 closely related codes in its exclusion list.
What is the ICD-9 equivalent of K35.80?
Under the General Equivalence Mappings, unspecified acute appendicitis converts to ICD-9-CM 540.9 (acute appendicitis NOS). The mapping is approximate, so confirm the match fits the documentation.
