What is ICD-10 code K51.018?

K51.018 is the ICD-10-CM diagnosis code for Ulcerative (chronic) pancolitis with other complication. A chronic inflammatory condition affecting the entire colon with a complication other than rectal bleeding, obstruction, fistula, or abscess. This code captures less common complications of ulcerative pancolitis. K51.018 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. K51.018 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. K51.018 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. K51.018 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Which HCC does K51.018 map to under V28?

K51.018 maps to CMS-HCC V28 81 (Ulcerative Colitis). The category number and label come from the CMS-HCC V28 model file for payment year 2026.

What does K51.018 pay in RAF?

K51.018 carries a community, non-dual, aged (CNA) RAF weight of 0.244 under CMS-HCC V28 for payment year 2026. The weight comes from the CMS V28 relative-factor file, not a hand-typed table.

What is the V28 vs V24 difference for K51.018?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For K51.018, V28 maps to Ulcerative Colitis at RAF 0.244 while V24 mapped to Inflammatory Bowel Disease at RAF 0.308. Both models can still appear in legacy data and in payer-specific lookback periods.

What documentation supports K51.018?

Clearly document the specific complication in the medical record (e.g., toxic megacolon, perforation, arthritis) Use this code only when the complication does not fit into the more specific K51.011-K51.014 categories Because K51.018 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score. See the MEAT criteria checklist at /meat-criteria for what Monitor, Evaluate, Assess, or Treat looks like in a note. MEAT is generic documentation evidence, not a payer-specific rule.

2026 ICD-10-CM K51.018: Ulcerative (chronic)

K51.018 maps to CMS-HCC V28 81 (RAF 0.244). Documentation must support MEAT. MEAT criteria · RAF calculator · HCC coding software

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Code lookupK51.018Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Diseases of the digestive system (K00-K95) / Noninfective enteritis and colitis (K50-K52)

K51.018

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Ulcerative (chronic) pancolitis with other complication

A chronic inflammatory condition affecting the entire colon with a complication other than rectal bleeding, obstruction, fistula, or abscess. This code captures less common complications of ulcerative pancolitis.

Buddy Insight

Ulcerative pancolitis with other complication captures less common but clinically significant complications such as toxic megacolon, perforation, extraintestinal manifestations (arthritis, pyoderma gangrenosum, primary sclerosing cholangitis), or other sequelae.

CMS-HCC V28

Mapped

HCC 81

Ulcerative Colitis

RAF 0.244

CMS-HCC V24

Mapped

HCC 35

Inflammatory Bowel Disease

RAF 0.308

ACA/HHS

Mapped

HCC 48

HHS-HCC 48

Varies by metal level

ESRD/PACE

Mapped

HCC 35

Inflammatory Bowel Disease

RAF 0.048

RXHCC

Mapped

HCC 67

Inflammatory Bowel Disease

RAF 0.494

Code Book Path

Official

K51.0Ulcerative (chronic) pancolitis

K51.01Ulcerative (chronic) pancolitis with complications

K51.018Ulcerative (chronic) pancolitis with other complication

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for K51.018 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for K51.018 in this effective period.

Related Child Codes

Official

K51.011Ulcerative (chronic) pancolitis with rectal bleeding

K51.012Ulcerative (chronic) pancolitis with intestinal obstruction

K51.013Ulcerative (chronic) pancolitis with fistula

K51.014Ulcerative (chronic) pancolitis with abscess

K51.019Ulcerative (chronic) pancolitis with unspecified complications

Includes

Official

ICD-10-CM does not list Includes notes for K51.018 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for K51.018 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for K51.018 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for K51.018 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for K51.018 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Confirmed diagnosis of ulcerative colitis with pancolitis

Clear documentation of the specific complication that does not fit bleeding, obstruction, fistula, or abscess categories

Clinical evidence supporting the complication (imaging, labs, physical exam findings)

Provider statement linking the complication to the ulcerative colitis

MEAT Support

HCC Buddy guidance

Confirmed diagnosis of ulcerative colitis with pancolitis

Clear documentation of the specific complication that does not fit bleeding, obstruction, fistula, or abscess categories

Clinical evidence supporting the complication (imaging, labs, physical exam findings)

Provider statement linking the complication to the ulcerative colitis

Audit Caution

HCC Buddy guidance

Using this code when a more specific complication code exists (K51.011-K51.014)

Failing to document what the 'other complication' actually is in the medical record

Not coding extraintestinal manifestations separately when they require independent clinical management

Confusing 'other complication' (known but not in standard list) with 'unspecified complication' (unknown type)

Common Mistakes

HCC Buddy guidance

K51.018 vs K51.011-K51.014 — Use the more specific complication code if the complication is rectal bleeding, obstruction, fistula, or abscess

K51.018 vs K51.019 — K51.019 is for unspecified complications; use K51.018 when the complication is known but falls outside standard categories

K51.018 vs K51.00 — K51.00 is pancolitis without complications; ensure complications are properly captured

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is K51.018 an HCC code?

Yes. K51.018 (Ulcerative (chronic) pancolitis with other complication) maps to Ulcerative Colitis under the CMS-HCC V28 risk adjustment model (and Inflammatory Bowel Disease under V24), with a community non-dual aged RAF of 0.244. It is billable for payment year 2026.

Coder answer: K51.018 is billable and maps to V28 HCC 81, Ulcerative Colitis. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: K51.018
Description: Ulcerative (chronic) pancolitis with other complication
HCC (V28): HCC 81 — Ulcerative Colitis
RAF: 0.244
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 81, Ulcerative Colitis

0.244

V24HCC 35, Inflammatory Bowel Disease

0.308

ESRDHCC 35, Inflammatory Bowel Disease

0.048

RxHCCHCC 67, Inflammatory Bowel Disease

0.494

Each model's RAF is its CMS base weight for that model's standard population, so weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.

Work K51.018 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for K51.018

For K51.018 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.

MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
EEvaluate: test results, medication response, or physical findings reviewed by the provider
AAssess: explicit mention in the assessment or plan with acknowledgment of status
TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed K51.018 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

K51.018 is the ICD-10-CM diagnosis code for ulcerative (chronic) pancolitis with other complication. A chronic inflammatory condition affecting the entire colon with a complication other than rectal bleeding, obstruction, fistula, or abscess. This code captures less common complications of ulcerative pancolitis. K51.018 sits in the ICD-10-CM chapter for diseases of the digestive system (k00-k95), within the section covering noninfective enteritis and colitis (k50-k52).

Under the CMS-HCC V28 risk adjustment model, K51.018 maps to Ulcerative Colitis (HCC 81) with a community, non-dual, aged base RAF weight of 0.244. Under the older CMS-HCC V24 model, K51.018 maps to Inflammatory Bowel Disease (HCC 35) with a community, non-dual, aged base RAF weight of 0.308. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.

Clearly document the specific complication in the medical record (e.g., toxic megacolon, perforation, arthritis). Because K51.018 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for K51.018 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Clearly document the specific complication in the medical record (e.g., toxic megacolon, perforation, arthritis)
•Use this code only when the complication does not fit into the more specific K51.011-K51.014 categories

Clinical Significance

Documentation Requirements

✓Confirmed diagnosis of ulcerative colitis with pancolitis
✓Clear documentation of the specific complication that does not fit bleeding, obstruction, fistula, or abscess categories
✓Clinical evidence supporting the complication (imaging, labs, physical exam findings)
✓Provider statement linking the complication to the ulcerative colitis
✓Current treatment plan addressing both the colitis and the complication
✓Disease activity assessment and severity documentation

Commonly Confused Codes

•K51.018 vs K51.011-K51.014: Use the more specific complication code if the complication is rectal bleeding, obstruction, fistula, or abscess
•K51.018 vs K51.019: K51.019 is for unspecified complications; use K51.018 when the complication is known but falls outside standard categories
•K51.018 vs K51.00: K51.00 is pancolitis without complications; ensure complications are properly captured