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K51.90 ICD-10-CM Code: Ulcerative colitis, unspecified, without complications

K51.90 maps to CMS-HCC V28 81 (RAF 0.244). Documentation must support MEAT. MEAT criteria · RAF calculator · HCC coding software

ICD-10-CM Code View

HCC Buddy Code Card

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

K51.90

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

Ulcerative colitis, unspecified, without complications

Ulcerative colitis of unspecified extent without any complications.

Buddy the Bee presenting code insight

Buddy Insight

Ulcerative colitis, unspecified, without complications is used when ulcerative colitis is diagnosed but the anatomic extent is not documented.

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
K51Ulcerative colitis
K51.9Ulcerative colitis, unspecified
K51.90Ulcerative colitis, unspecified, without complications

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for K51.90 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for K51.90 in this effective period.

Related Child Codes

Official
K51.91Ulcerative colitis, unspecified, with complications

Includes

Official

ICD-10-CM does not list Includes notes for K51.90 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for K51.90 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for K51.90 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for K51.90 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for K51.90 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
Confirmed diagnosis of ulcerative colitis
Documentation that extent cannot be determined from available records
Statement confirming no complications are present
Treatment plan appropriate for ulcerative colitis

MEAT Support

HCC Buddy guidance
Confirmed diagnosis of ulcerative colitis
Documentation that extent cannot be determined from available records
Statement confirming no complications are present
Treatment plan appropriate for ulcerative colitis

Audit Caution

HCC Buddy guidance
Using this unspecified code when colonoscopy reports document the anatomic extent of disease
Not querying the provider for disease extent when it is clinically determinable
Confusing ulcerative colitis with Crohn disease — they require different code categories
Using this code for non-ulcerative forms of colitis (infectious, ischemic, microscopic)

Common Mistakes

HCC Buddy guidance
K51.90 vs K51.00/K51.20/K51.30/K51.50 — Use anatomically specific codes when extent is documented
K51.90 vs K52.9 — K52.9 is noninfective colitis unspecified (not necessarily ulcerative colitis)
K51.90 vs K51.80 — K51.80 is 'other' ulcerative colitis (known but non-standard); K51.90 is truly unspecified
K51.90 vs K50.90 — K50.90 is Crohn disease unspecified; these are different diseases

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 K51.90 an HCC code?

Yes. K51.90 (Ulcerative colitis, unspecified, without complications) 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: K51.90 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
K51.90
Description
Ulcerative colitis, unspecified, without complications
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 K51.90 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for K51.90

For K51.90 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 K51.90 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

K51.90 is the ICD-10-CM diagnosis code for ulcerative colitis, unspecified, without complications. Ulcerative colitis of unspecified extent without any complications. K51.90 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, K51.90 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, K51.90 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.

This is a default code when the extent of ulcerative colitis is not documented; query for disease extent (proctitis, left-sided, pancolitis) if possible. Because K51.90 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 K51.90 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •This is a default code when the extent of ulcerative colitis is not documented; query for disease extent (proctitis, left-sided, pancolitis) if possible.
  • •Use only when no complications are present; if any complication exists, select the appropriate K51.91x code instead.

Clinical Significance

Ulcerative colitis, unspecified, without complications is used when ulcerative colitis is diagnosed but the anatomic extent is not documented. While this code captures the fundamental diagnosis, it represents a missed opportunity for specificity. The anatomic extent of ulcerative colitis directly impacts treatment decisions, cancer surveillance intervals, and prognosis.

Documentation Requirements

  • ✓Confirmed diagnosis of ulcerative colitis
  • ✓Documentation that extent cannot be determined from available records
  • ✓Statement confirming no complications are present
  • ✓Treatment plan appropriate for ulcerative colitis
  • ✓Plan for colonoscopy to determine disease extent if not yet performed
  • ✓Evidence of provider query for disease extent if available

Commonly Confused Codes

  • •K51.90 vs K51.00/K51.20/K51.30/K51.50: Use anatomically specific codes when extent is documented
  • •K51.90 vs K52.9: K52.9 is noninfective colitis unspecified (not necessarily ulcerative colitis)
  • •K51.90 vs K51.80: K51.80 is 'other' ulcerative colitis (known but non-standard); K51.90 is truly unspecified
  • •K51.90 vs K50.90: K50.90 is Crohn disease unspecified; these are different diseases

Child Codes

K51.90Ulcerative colitis, unspecified, without complications
HCC 81
K51.91Ulcerative colitis, unspecified, with complications

Code Hierarchy

└K51Ulcerative colitis└K51.9Ulcerative colitis, unspecified└K51.90Ulcerative colitis, unspecified, without complications
└K51.90Ulcerative colitis, unspecified, without complications

Also searched as

  • UC
  • ulcerative colitis

Because K51.90 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.

K51.90 maps to CMS-HCC V28 category 81, Ulcerative Colitis. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. Because K51.90 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 K51.90 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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