K58.9: Irritable bowel syndrome, unspecified

The ICD-10-CM code for irritable bowel syndrome when the provider documents IBS without naming the predominant bowel habit pattern.

Billable

FY2027

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At a glance

Code Family

K58: Irritable bowel syndrome.

Condition

Irritable bowel syndrome

Billable

Yes, valid for HIPAA-covered transactions.

HCC Mapping (v28)

None. K58.9 carries no HCC category under CMS-HCC v28.

DRG Grouping

MS-DRG 391 or 392 under the FY2027 MS-DRG v44 grouper, split on the presence of a major complication or comorbidity.

Family Specificity

Five billable child codes structured around the documented predominant bowel habit pattern, with K58.9 as the residual code when no subtype is recorded.

Which K58 code do I assign?

The K58 family splits on the predominant bowel habit pattern the provider records, not on the severity of the disorder. Reserve K58.9 for a note that documents irritable bowel syndrome without naming a diarrhea, constipation or mixed pattern.

When documentation says…

Code

IBS with diarrhea, IBS-D

K58.0

Irritable bowel syndrome with diarrhea. The note must document diarrhea as the predominant bowel habit. Code selection follows the provider's documented diagnosis, not symptom inference.

IBS with constipation, IBS-C

K58.1

Irritable bowel syndrome with constipation. The note must document constipation as the predominant bowel habit.

Mixed IBS, IBS-M, alternating diarrhea and constipation

K58.2

Mixed irritable bowel syndrome. The note must document an alternating pattern rather than a single predominant habit.

Other specified irritable bowel syndrome

K58.8

Other irritable bowel syndrome. Use this code when the provider documents a specified IBS subtype that the named child codes do not cover.

Irritable bowel syndrome, no subtype stated

K58.9

Irritable bowel syndrome, unspecified. Use this code when the record documents IBS or irritable bowel syndrome without a predominant bowel habit pattern. Query the provider where the clinical documentation supports a specific pattern.

Abdominal pain with no IBS diagnosis recorded

R10.-

Abdominal and pelvic pain. Assign a code from the R10 codes where the provider has not documented irritable bowel syndrome. The diagnosis is not inferred from symptoms.

Crohn's disease or ulcerative colitis

K50.-

Crohn's disease, an inflammatory bowel disease coded outside the K58 category. Ulcerative colitis takes a code from the K51 codes. Provider documentation governs the distinction between inflammatory and functional disease.

Tabular notes

USE ADDITIONAL

K58.9 carries no mandatory tabular level Use Additional, Code First or Code Also instruction. Comorbid conditions are reported separately when the provider documents them.

FY2027: EFFECTIVE 1 OCTOBER 2026

K58.9 is valid in the FY2026 code set and unchanged in the FY2027 update, which took effect on 1 October 2026. The FY2027 code and tabular addenda add, delete or revise nothing in category K58. K58.9 sits in chapter 11, diseases of the digestive system, within the K55–K64 block for other diseases of intestines.

Operational & financial impact

Why specificity matters beyond the chart: risk adjustment, DRG assignment and denial exposure all follow from which code is selected.

CMS-HCC v28 (PY2024+)

K58.9 maps to no HCC category under CMS-HCC v28.

The code carried no HCC mapping under CMS-HCC v24 either.

No code in category K58 maps to a v28 category. Irritable bowel syndrome is a functional disorder without an HCC mapping.

Conditions documented alongside irritable bowel syndrome, such as anxiety or depression, may carry HCC weight where they map.

MS-DRG v44 (FY2027)

K58.9 as a principal inpatient diagnosis groups under MDC 06, diseases and disorders of the digestive system, in the FY2027 MS-DRG v44 grouper.

MS-DRG 391: Esophagitis, gastroenteritis and miscellaneous digestive disorders with MCC.

MS-DRG 392: Esophagitis, gastroenteritis and miscellaneous digestive disorders without MCC.

The structure is two tier, split on the presence of a major complication or comorbidity.

Where irritable bowel syndrome is comorbid with the reason for admission, K58.9 is reported as a secondary diagnosis.

Medicare and commercial payers

K58.9 is a valid billable code and is not rejected as an incomplete code.

WHERE SPECIFICITY IS LOST

K58.9 records irritable bowel syndrome without the predominant bowel habit pattern.

Assigning it where the provider has documented a subtype discards the detail that K58.0, K58.1 and K58.2 carry.

Documentation checklist to support K58.9

Chart elements that support code selection and reduce specificity-driven denials.

Explicit documentation of irritable bowel syndrome or IBS as a clinical diagnosis, rather than abdominal pain or altered bowel habits alone.

The absence of any subtype specification. Where a diarrhea predominant, constipation predominant or mixed pattern is documented, assign K58.0, K58.1 or K58.2 instead.

The clinical basis for the diagnosis, which rests on Rome IV criteria rather than on a definitive structural or biochemical marker.

A provider query where the clinical documentation supports a predominant bowel habit pattern but the note does not name it.

Separation of irritable bowel syndrome from inflammatory bowel disease in the note. Crohn's disease and ulcerative colitis are coded outside the K58 category.

Documented comorbidities such as generalized anxiety disorder or a depressive disorder, where these are to be reported alongside K58.9.

The setting of care. K58.9 is managed in gastroenterology and primary care on the outpatient side. On inpatient records it is a secondary diagnosis when another condition accounts for the admission.

FAQ

Is K58.9 a billable code?

Yes. K58.9 is billable and valid for HIPAA-covered transactions. It is the residual code in the K58 category for irritable bowel syndrome recorded without a subtype.

When should I use K58.9 instead of K58.0?

Use K58.0 when the provider documents IBS with diarrhea or IBS-D. Use K58.9 when the note records irritable bowel syndrome without naming a predominant bowel habit pattern. Code selection follows the documented diagnosis, not symptom inference.

Does K58.9 map to an HCC?

No. K58.9 maps to no HCC category under CMS-HCC v28. It carried no mapping under CMS-HCC v24 either. Irritable bowel syndrome is a functional disorder without an HCC mapping.

What must the provider document to support K58.9?

The note must state irritable bowel syndrome or IBS as a clinical diagnosis. Abdominal pain or altered bowel habits alone will not support the code. The note must also leave the predominant bowel habit pattern unspecified.

How is irritable bowel syndrome distinguished from inflammatory bowel disease?

Irritable bowel syndrome is a functional disorder coded in the K58 category. Inflammatory bowel disease is inflammatory and is coded as Crohn's disease under K50 or as ulcerative colitis under K51. Provider documentation governs the distinction. Do not substitute one for the other on clinical inference.

What changed for K58.9 in FY2027?

K58.9 is unchanged in the FY2027 update, effective 1 October 2026, which adds, deletes or revises nothing in category K58. No FY2026 changes were identified for K58.9 or for the parent K58 category. The code family and the subtype structure remained stable in FY2026.

How does K58.9 behave on an inpatient claim?

As a principal diagnosis, K58.9 groups under MDC 06 in the FY2027 MS-DRG v44 grouper. It falls to MS-DRG 391 with a major complication or comorbidity and to MS-DRG 392 without one. Where irritable bowel syndrome is comorbid with the reason for admission, it is reported as a secondary diagnosis.

What coding errors should I watch for with K58.9?

Three errors apply to K58.9. The first is assigning K58.9 where the provider has documented the subtype, which calls for K58.0, K58.1 or K58.2. The second is coding K58.9 for abdominal pain where no IBS diagnosis is recorded, which calls for a code from the R10 codes. The third is substituting a K58 code for an inflammatory bowel disease code, or the reverse.

Related codes

Codes in the same family as K58.9. Only codes with a published page render as links.

Sibling codes in the K58 family

K58.0: Irritable bowel syndrome with diarrhea.
K58.1: Irritable bowel syndrome with constipation.
K58.2: Mixed irritable bowel syndrome.
K58.8: Other irritable bowel syndrome.

Additional codes to consider

Codes outside the K58 family considered alongside K58.9.

Consider instead

K50-: Crohn's disease [regional enteritis], an inflammatory bowel disease coded outside the K58 category.
K51-: Ulcerative colitis, an inflammatory bowel disease coded outside the K58 category.
R10-: Abdominal and pelvic pain, where the provider has not documented irritable bowel syndrome.

Sources

All claims on this page derive from government and professional-standards sources.

National Center for Health Statistics. (2026). International classification of diseases, tenth revision, clinical modification (ICD-10-CM) FY2027 files. https://www.cdc.gov/nchs/icd/icd-10-cm/files.html
Centers for Medicare & Medicaid Services and National Center for Health Statistics. (2026). ICD-10-CM official guidelines for coding and reporting FY2027. https://ftp.cdc.gov/pub/Health_Statistics/NCHS/Publications/ICD10CM/2027/ICD-10-CM-October-1-2026-FY27-Guidelines.pdf
Centers for Medicare & Medicaid Services. (2025). 2026 model software/ICD-10 mappings. https://www.cms.gov/medicare/payment/medicare-advantage-rates-statistics/risk-adjustment/2026-model-software-icd-10-mappings
Centers for Medicare & Medicaid Services. (2026). MS-DRG classifications and software, version 44. https://www.cms.gov/medicare/payment/prospective-payment-systems/acute-inpatient-pps/ms-drg-classifications-and-software