Unspecified appendicitis
In Diseases of appendix (K35-K38), chapter 11: Diseases of the Digestive System
- K37 is an unspecified code: use it only when the record doesn't document anything more specific. If the record has more detail, check the other codes under K35-K38 below.
- As a secondary diagnosis it is not a CC or MCC, so it doesn't raise the MS-DRG payment.
- Doesn't count toward a Medicare Advantage risk score (no HCC in V28).
- AHRQ's Chronic Condition Indicator classes it as not chronic (an acute or short-term condition).
- 100 US deaths in 2024 had an underlying cause in category K37, per the National Vital Statistics System on CDC WONDER. Death records use WHO ICD-10, so the count is for the whole category.
Also indexed as: Appendicitis; Perityphlitis
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Instructional notes
Official coding guidelines
From the ICD-10-CM Official Guidelines for Coding and Reporting, FY 2027 (CMS and NCHS). Links open the PDF at the right page.
There are no chapter-specific rules for Chapter 11 yet, so the general rules in Section I.B apply.
Other codes under K35-K38
Diseases of appendix (K35-K38)
- K35Acute appendicitis
- K36Other appendicitis
- K37Unspecified appendicitis(this code)
- K38Other diseases of appendix
K37 MS-DRGs
As the principal diagnosis, K37 groups to MS-DRG 393, 394, or 395 (v44.0). Which one applies depends on procedures performed, secondary diagnoses (CC/MCC), and the patient's age and discharge status.
Related conditions
Grouped by AHRQ's Clinical Classifications Software Refined (CCSR), which sorts every diagnosis code into clinically meaningful categories.
K37 is in Appendicitis and other appendiceal conditions (DIG009, its default category), with 21 codes. Others in it:
- K35.200 Acute appendicitis with generalized peritonitis, without perforation or abscess
- K35.201 Acute appendicitis with generalized peritonitis, with perforation, without abscess
- K35.209 Acute appendicitis with generalized peritonitis, without abscess, unspecified as to perforation
- K35.210 Acute appendicitis with generalized peritonitis, without perforation, with abscess
- K35.211 Acute appendicitis with generalized peritonitis, with perforation and abscess
- K35.219 Acute appendicitis with generalized peritonitis, with abscess, unspecified as to perforation
- K35.30 Acute appendicitis with localized peritonitis, without perforation or gangrene
- K35.31 Acute appendicitis with localized peritonitis and gangrene, without perforation
Medicare coverage articles listing K37
This Medicare billing and coding article lists K37 as a diagnosis that supports medical necessity for the services they cover. From the CMS Medicare Coverage Database; check your own contractor's article before billing.
About the condition
Plain-language background from MedlinePlus (National Library of Medicine), not coding guidance.
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. If the blockage is not treated, the appendix can burst and spread infection into the abdomen. This causes a condition called peritonitis.
Read more about appendicitis on MedlinePlusCode history
Valid since FY2016, when ICD-10-CM took effect on October 1, 2015. No changes since.
ICD-9-CM equivalent
Legacy crosswalk from the CMS General Equivalence Mappings (last updated 2018).
- 541 Appendicitis, unqualified