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K51.913 ICD-10-CM Code: Ulcerative colitis, unspecified with fistula

K51.913 maps to CMS-HCC V28 81 (RAF 0.244). Documentation must support MEAT. MEAT criteria · RAF calculator · free HCC coding tools

ICD-10-CM Code View

HCC Buddy Code Card

Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

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

K51.913

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

Ulcerative colitis, unspecified with fistula

Ulcerative colitis of unspecified extent with an abnormal tunnel-like connection between the colon and other tissues.

Buddy the Bee presenting code insight

Buddy Insight

Ulcerative colitis, unspecified, with fistula indicates fistula formation in ulcerative colitis of undetermined extent.

CMS-HCC V28

HCC 81

RAF 0.244

CMS-HCC V24

HCC 35

RAF 0.308

ACA/HHS

HCC 48

Varies by metal level

ESRD/PACE

HCC 35

RAF 0.048

RXHCC

HCC 67

RAF 0.494

Code Book Path

Official
K51.9Ulcerative colitis, unspecified
K51.91Ulcerative colitis, unspecified, with complications
K51.913Ulcerative colitis, unspecified with fistula

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for K51.913 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for K51.913 in this effective period.

Related Child Codes

Official
K51.911Ulcerative colitis, unspecified with rectal bleeding
K51.912Ulcerative colitis, unspecified with intestinal obstruction
K51.914Ulcerative colitis, unspecified with abscess
K51.918Ulcerative colitis, unspecified with other complication
K51.919Ulcerative colitis, unspecified with unspecified complications

Includes

Official

ICD-10-CM does not list Includes notes for K51.913 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for K51.913 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for K51.913 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for K51.913 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for K51.913 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
Confirmed ulcerative colitis diagnosis
Documentation of fistula type and location
Imaging confirmation of fistula
Provider statement linking fistula to the colitis

MEAT Support

HCC Buddy guidance
Confirmed ulcerative colitis diagnosis
Documentation of fistula type and location
Imaging confirmation of fistula
Provider statement linking fistula to the colitis

Audit Caution

HCC Buddy guidance
Not reconsidering a Crohn disease diagnosis when fistula occurs in ulcerative colitis
Using this unspecified code when disease extent has been determined
Coding fistula separately instead of using the combination code
Not documenting fistula type and location

Common Mistakes

HCC Buddy guidance
K51.913 vs K50.x13 — Crohn disease with fistula; reconsider diagnosis when fistula is present
K51.913 vs K60.3 — K60.3 is anal fistula unrelated to inflammatory bowel disease
K51.913 vs K51.013/K51.213/K51.313/K51.513/K51.813 — Use extent-specific codes when extent is known

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 K51.913 an HCC code?

Yes. K51.913 (Ulcerative colitis, unspecified with fistula) 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: K51.913 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
K51.913
Description
Ulcerative colitis, unspecified with fistula
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 K51.913 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for K51.913

For K51.913 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 K51.913 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

K51.913 is the ICD-10-CM diagnosis code for ulcerative colitis, unspecified with fistula. Ulcerative colitis of unspecified extent with an abnormal tunnel-like connection between the colon and other tissues. K51.913 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, K51.913 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, K51.913 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.

Document the location and type of fistula (enterocutaneous, rectovaginal, etc.) for complete clinical documentation. Because K51.913 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 K51.913 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •Document the location and type of fistula (enterocutaneous, rectovaginal, etc.) for complete clinical documentation.
  • •Fistulas in ulcerative colitis may require additional codes if they involve other organs or require separate treatment.

Clinical Significance

Ulcerative colitis, unspecified, with fistula indicates fistula formation in ulcerative colitis of undetermined extent. The presence of a fistula is unusual for ulcerative colitis and should prompt both determination of disease extent and reconsideration of whether the diagnosis might be Crohn disease, which is far more commonly associated with fistulizing disease.

Documentation Requirements

  • ✓Confirmed ulcerative colitis diagnosis
  • ✓Documentation of fistula type and location
  • ✓Imaging confirmation of fistula
  • ✓Provider statement linking fistula to the colitis
  • ✓Documentation of diagnostic reconsideration for Crohn disease
  • ✓Surgical consultation and treatment plan

Commonly Confused Codes

  • •K51.913 vs K50.x13: Crohn disease with fistula; reconsider diagnosis when fistula is present
  • •K51.913 vs K60.3: K60.3 is anal fistula unrelated to inflammatory bowel disease
  • •K51.913 vs K51.013/K51.213/K51.313/K51.513/K51.813: Use extent-specific codes when extent is known

Child Codes

K51.911Ulcerative colitis, unspecified with rectal bleeding
HCC 81
K51.912Ulcerative colitis, unspecified with intestinal obstruction
HCC 78
K51.913Ulcerative colitis, unspecified with fistula
HCC 81
K51.914Ulcerative colitis, unspecified with abscess
HCC 81
K51.918Ulcerative colitis, unspecified with other complication
HCC 81
K51.919Ulcerative colitis, unspecified with unspecified complications
HCC 81

Code Hierarchy

└K51Ulcerative colitis└K51.9Ulcerative colitis, unspecified└K51.91Ulcerative colitis, unspecified, with complications└K51.913Ulcerative colitis, unspecified with fistula
└K51.913Ulcerative colitis, unspecified with fistula

Because K51.913 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.

K51.913 maps to CMS-HCC V28 category 81, Ulcerative Colitis. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. Because K51.913 carries a payment HCC, you can see what it adds to a RAF score and check the documentation the chart needs before it is submitted.

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Open K51.913 in the Code Book for the full Index-to-Tabular path, MEAT checklist, and V28 HCC mapping, or in the Encoder to code from a keyword search. Pro includes 7 days to try everything, no card required.

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