2027 ICD-10-CM Diagnosis Code K59.31Toxic megacolon
ICD-10-CM Codes›K00–K95›K55-K64›K59
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Risk Adjusts — HCC 78
- Not Chronic
K59.31 is a billable ICD-10-CM diagnosis code for toxic megacolon. 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 15 closely related codes. Coders also document this condition as drug-induced megacolon. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Drug induced or toxic related condition and Other specified and unspecified gastrointestinal disorders.
For Medicare Advantage risk adjustment, K59.31 maps to CMS-HCC Category 78 (Intestinal Obstruction/Perforation) under the V28 model, adding a risk factor of about 0.326 for a community, non-dual, aged beneficiary in payment year 2027.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
K59.31 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2027.
Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Drug-induced megacolon
- Secondary acquired megacolon
- Toxic megacolon due to ulcerative colitis
- Toxic state
- Toxic state due to colonic dilatation
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to K59.31: its own notes plus those printed at K59.3, K59, and Chapter 11. A note printed at a category, block or chapter applies to every code under it.
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
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.
- functional disorders of stomach (K31.-)
- 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)
Code First
The underlying condition named in the note is sequenced before this code.
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name K59.31, its category, or a range that includes it.
Excludes1 1
These codes carry an Excludes1 note naming K59.31: they are not reported together with it, unless the two conditions are unrelated.
- Block K50-K52 Noninfective enteritis and colitismegacolon (K59.3-) names K59.3-, which includes this code
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Megacolon, Toxic
an acute form of megacolon, severe pathological dilatation of the colon. it is associated with clinical conditions such as ulcerative colitis; crohn disease; amebic dysentery; or clostridium enterocolitis.
Patient EducationClinical
Colonic Diseases
Your colon, also known as the large intestine, is part of your digestive system. It's a long, hollow tube at the end of your digestive tract where your body makes and stores stool. Many disorders affect the colon's ability to work properly. Some of these include:
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert K59.31 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code History & ChangesHistory
Replacement K59.31 replaces the following previously assigned code(s):
- K59.3 - Megacolon, not elsewhere classified
Questions About K59.31Overview
What is the ICD-10 code for toxic megacolon?
The ICD-10-CM code for toxic megacolon is K59.31 (sometimes written as K5931). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is K59.31 (Megacolon, not elsewhere classified) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report toxic megacolon on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does K59.31 group to?
When toxic megacolon 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 K59.31 a CC or MCC?
CMS lists K59.31 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 15 closely related codes in its exclusion list.
Can K59.31 be reported with Q43.1?
Not as a rule. The Excludes1 note at K59.3, which applies to K59.31, lists "congenital megacolon (aganglionic) (Q43.1)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).
What HCC is K59.31?
K59.31 (toxic megacolon) maps to CMS-HCC Category 78 (Intestinal Obstruction/Perforation), commonly written as HCC 78, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 33 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. It does not map to any RxHCC in the Part D prescription drug model.
Does K59.31 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, K59.31 adds a risk adjustment factor of about 0.326 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.326 to 0.688 depending on the payment segment). A more severe related category (HCC 77) supersedes it when both are reported. See the full factor table on the HCC 78 category page.
