What is ICD-10 code K51.311?

K51.311 is the ICD-10-CM diagnosis code for Ulcerative (chronic) rectosigmoiditis with rectal bleeding. Chronic inflammation with ulcers in the rectum and sigmoid colon that is causing bleeding from the rectum. It belongs to the ICD-10-CM chapter for diseases of the digestive system (k00-k95). K51.311 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. K51.311 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. K51.311 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. K51.311 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.

What is the V28 vs V24 difference for K51.311?

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 K51.311, 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 should coders know when reporting K51.311?

Verify rectal bleeding is documented and attributed to the ulcerative rectosigmoiditis This is a common complication; ensure bleeding is specifically noted in the record Because K51.311 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.

2026 ICD-10-CM K51.311: Ulcerative (chronic)

ICD-10-CM Code View

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Code lookupK51.311Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

K51.311

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

Ulcerative (chronic) rectosigmoiditis with rectal bleeding

Chronic inflammation with ulcers in the rectum and sigmoid colon that is causing bleeding from the rectum.

Buddy Insight

Ulcerative rectosigmoiditis with rectal bleeding indicates active hemorrhagic complication of inflammation in the rectum and sigmoid colon.

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

K51.3Ulcerative (chronic) rectosigmoiditis

K51.31Ulcerative (chronic) rectosigmoiditis with complications

K51.311Ulcerative (chronic) rectosigmoiditis with rectal bleeding

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for K51.311 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for K51.311 in this effective period.

Related Child Codes

Official

K51.312Ulcerative (chronic) rectosigmoiditis with intestinal obstruction

K51.313Ulcerative (chronic) rectosigmoiditis with fistula

K51.314Ulcerative (chronic) rectosigmoiditis with abscess

K51.318Ulcerative (chronic) rectosigmoiditis with other complication

K51.319Ulcerative (chronic) rectosigmoiditis with unspecified complications

Includes

Official

ICD-10-CM does not list Includes notes for K51.311 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for K51.311 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for K51.311 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for K51.311 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for K51.311 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Confirmed ulcerative colitis involving rectum and sigmoid colon

Documentation of rectal bleeding including frequency and severity

Provider attribution of bleeding to the rectosigmoiditis

Laboratory values (hemoglobin, hematocrit) if clinically significant bleeding

MEAT Support

HCC Buddy guidance

Confirmed ulcerative colitis involving rectum and sigmoid colon

Documentation of rectal bleeding including frequency and severity

Provider attribution of bleeding to the rectosigmoiditis

Laboratory values (hemoglobin, hematocrit) if clinically significant bleeding

Audit Caution

HCC Buddy guidance

Separating the bleeding from the colitis diagnosis instead of using the combination code

Not distinguishing between active bleeding during a flare versus historical bleeding

Using the uncomplicated code K51.30 when rectal bleeding is documented

Defaulting to unspecified ulcerative colitis (K51.911) when the anatomic extent is documented

Common Mistakes

HCC Buddy guidance

K51.311 vs K51.011 — K51.011 is pancolitis with rectal bleeding (entire colon); rectosigmoiditis is more limited

K51.311 vs K51.211 — K51.211 is proctitis with rectal bleeding (rectum only)

K51.311 vs K51.511 — K51.511 is left-sided colitis with rectal bleeding (extends to descending colon)

K51.311 vs K62.5 — K62.5 is hemorrhage of anus and rectum without inflammatory bowel disease

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 K51.311 an HCC code?

Yes. K51.311 (Ulcerative (chronic) rectosigmoiditis with rectal bleeding) 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: K51.311 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: K51.311
Description: Ulcerative (chronic) rectosigmoiditis with rectal bleeding
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 K51.311 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for K51.311

For K51.311 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 K51.311 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

K51.311 is the ICD-10-CM diagnosis code for ulcerative (chronic) rectosigmoiditis with rectal bleeding. Chronic inflammation with ulcers in the rectum and sigmoid colon that is causing bleeding from the rectum. K51.311 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, K51.311 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, K51.311 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.

Verify rectal bleeding is documented and attributed to the ulcerative rectosigmoiditis. Because K51.311 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 K51.311 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Verify rectal bleeding is documented and attributed to the ulcerative rectosigmoiditis
•This is a common complication; ensure bleeding is specifically noted in the record

Clinical Significance

Ulcerative rectosigmoiditis with rectal bleeding indicates active hemorrhagic complication of inflammation in the rectum and sigmoid colon. Bleeding from this anatomic distribution is a common manifestation of disease flare and may require treatment escalation, iron supplementation, or transfusion in severe cases.

Documentation Requirements

✓Confirmed ulcerative colitis involving rectum and sigmoid colon
✓Documentation of rectal bleeding including frequency and severity
✓Provider attribution of bleeding to the rectosigmoiditis
✓Laboratory values (hemoglobin, hematocrit) if clinically significant bleeding
✓Treatment plan addressing active disease and bleeding
✓Disease activity assessment

Commonly Confused Codes

•K51.311 vs K51.011: K51.011 is pancolitis with rectal bleeding (entire colon); rectosigmoiditis is more limited
•K51.311 vs K51.211: K51.211 is proctitis with rectal bleeding (rectum only)
•K51.311 vs K51.511: K51.511 is left-sided colitis with rectal bleeding (extends to descending colon)
•K51.311 vs K62.5: K62.5 is hemorrhage of anus and rectum without inflammatory bowel disease