K59.00: Constipation, unspecified

The ICD-10-CM code for constipation when the provider documents the diagnosis without specifying the subtype, mechanism or cause.

Billable

FY2027

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At a glance

Code Family

K59.0: Constipation, a subcategory of K59 in chapter 11, Diseases of the digestive system (K00–K95).

DRG Grouping

MS-DRG 391 or 392 within MDC 06 under the FY2027 MS-DRG v44 grouper, depending on whether an MCC is also reported. K59.00 can be the principal diagnosis when constipation is the condition chiefly responsible for the admission. It is a secondary diagnosis when another condition accounts for the admission. When fecal impaction is documented, K56.41 is coded instead.

HCC Mapping (v28)

No HCC mapping: K59.00 does not map to any CMS-HCC v28 category, and it carried no mapping in v24 either.

Condition

Constipation

Family Specificity

Six codes in the K59.0 subcategory: K59.00, K59.01, K59.02, K59.03, K59.04 and K59.09, separating unspecified constipation from slow transit, outlet dysfunction, drug induced, chronic idiopathic and other constipation.

Which constipation code do I assign?

K59.00 is the not-otherwise-specified entry point for the K59.0 subcategory. The first question is always whether the record names a subtype, mechanism or cause. When one is documented, the specific code applies. K59.00 is most appropriate at initial presentation or when the etiology remains unestablished.

When documentation says…

Code

Constipation caused by a medication the patient is taking

K59.03

Drug induced constipation. Do not leave the encounter on K59.00 when the drug-induced nature is documented. For an adverse effect of a correctly prescribed and properly administered drug, K59.03 is sequenced first. The T36-T50 code with fifth or sixth character 5 follows it.

Chronic idiopathic constipation, or constipation the provider calls functional

K59.04

The term functional constipation belongs to K59.04, not to K59.00.

Slow transit confirmed, for example on colonic transit studies

K59.01

Slow transit constipation.

Constipation attributed to outlet dysfunction

K59.02

Outlet dysfunction constipation.

A named form of constipation with no dedicated code elsewhere in the subcategory

K59.09

Other constipation.

Fecal impaction documented

K56.41

An Excludes1 with K59.0x. Impaction is coded instead of constipation. Impaction is a complication beyond uncomplicated constipation.

Constipation documented as the manifestation of a psychogenic intestinal disorder

F45.8

An Excludes1 inherited from the K59 parent category.

A change in bowel habit with no confirmed diagnosis of constipation

R19.4

Change in bowel habit NOS, an Excludes1 inherited from the K59 parent category.

Constipation documented as a confirmed diagnosis with no subtype, mechanism or cause given

K59.00

The unspecified code. Per the Official Guidelines, a more specific code is preferred whenever one is available and supported by the documentation. Reach for K59.00 only when nothing more precise is documented.

Tabular notes

IMPORTANT DISTINCTION

K59.00 is Constipation, unspecified. It is not functional constipation. Chronic idiopathic constipation, also termed functional constipation, is K59.04. The Index sends Constipation, functional to K59.04, where Functional constipation is an inclusion term.

EXCLUDES1 AT THE K59.0 SUBCATEGORY LEVEL

Fecal impaction (K56.41). This is a Type 1 exclude. K59.00 and K56.41 are not reported together for the same condition. When fecal impaction is documented, use K56.41 instead of K59.00.

EXCLUDES2 AT THE K59.0 SUBCATEGORY LEVEL

Incomplete defecation (R15.0). This is a Type 2 exclude. K59.00 and R15.0 may be coded together when both are independently documented.

EXCLUDES1 AT THE K59 CATEGORY LEVEL

Change in bowel habit NOS (R19.4), intestinal malabsorption (K90.-) and psychogenic intestinal disorders (F45.8). These parent-level Type 1 excludes propagate to K59.00. When a psychogenic intestinal disorder is the documented basis for the constipation, use F45.8 rather than K59.00.

EXCLUDES2 AT THE K59 CATEGORY LEVEL

Functional disorders of stomach (the K31 codes). This is a Type 2 exclude at the category level. Concurrent coding with a K31.x code is permitted when both conditions are independently documented.

FY2027 CHANGES

K59.00 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 K59. No Excludes note at K59 or K59.0 changed.

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+)

No HCC mapping applies. K59.00 does not map to any Hierarchical Condition Category in CMS-HCC Model Version 28, which is fully operative at 100 percent weight for Medicare Advantage payment year 2026. No code in the K59.0 constipation subcategory maps to a category under either v28 or the prior v24 model. Reporting K59.00 does not contribute to a beneficiary's risk score.

SEQUENCING

Sequence K59.00 as the principal or primary diagnosis when unspecified constipation is the reason for the encounter and no underlying cause requiring code-first sequencing is documented. When the constipation is an adverse effect of a correctly prescribed and properly administered drug, sequence K59.03 first. The adverse effect code from T36-T50 with a fifth or sixth character of 5 follows it (Guideline I.C.19.e.5.(a)).

MEDICARE AND PAYER COVERAGE

There is no National Coverage Determination specific to K59.00.

WHERE SPECIFICITY IS LOST

K59.00 becomes the default whenever a documented subtype is overlooked. Specificity is lost when the code is labeled functional constipation, when it stays in place after drug induced constipation is documented and when it is not updated once the subtype is established.

Documentation checklist to support K59.00

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

Provider documentation of constipation as a confirmed diagnosis addressed at the encounter.

No documented subtype, mechanism or cause. Drug induced constipation requires K59.03 and confirmed slow transit constipation requires K59.01.

Confirmation that fecal impaction is not documented, since impaction is coded K56.41 under the Excludes1 rule.

Confirmation that the constipation is not documented as psychogenic in origin, which would direct the encounter to F45.8.

A provider query when constipation is documented alongside a medication such as an opioid, an anticholinergic or an iron supplement, to establish whether drug induced constipation is intended.

A review at follow-up so that the code is updated when the subtype is established, such as a medication identified as the cause or slow transit confirmed on colonic transit studies.

FAQ

Is K59.00 the code for functional constipation?

No. K59.00 is Constipation, unspecified. Functional constipation, also termed chronic idiopathic constipation, is K59.04. Labeling K59.00 as functional constipation misstates the tabular description. The Index sends Constipation, functional to K59.04.

Can K59.00 and K56.41 be reported on the same encounter?

K59.00 and K56.41 are not reported together for the same condition. Fecal impaction is an Excludes1 at the K59.0 subcategory level. When fecal impaction is documented, K56.41 is used instead of K59.00 because impaction represents a complication beyond uncomplicated constipation.

Can K59.00 and R15.0 be coded together?

Yes. Incomplete defecation is an Excludes2 at the K59.0 level, which permits concurrent coding. K59.00 and R15.0 may both be reported when each is independently documented.

What if a medication is causing the constipation?

Use K59.03, drug induced constipation, rather than K59.00. When the constipation is an adverse effect of a correctly prescribed and properly administered drug, sequence K59.03 first. The adverse effect code from T36-T50 with a fifth or sixth character of 5 follows it, under Guideline I.C.19.e.5.(a) and the Use additional code note at K59.03. When constipation is documented alongside opioids, anticholinergics or iron supplements, query the provider about whether drug induced constipation is intended.

Does K59.00 affect risk adjustment?

No. K59.00 does not map to any HCC in CMS-HCC v28 or in the prior v24 model. Reporting it does not contribute to a beneficiary's risk score.

What happens when the subtype is identified after the first visit?

Update the code. K59.00 is most appropriate at initial presentation or while the etiology remains unestablished. Once the cause is identified during subsequent evaluation, the more specific subcode applies, such as K59.03 when a medication is the cause or K59.01 when slow transit is confirmed.

Is K59.00 appropriate as an inpatient principal diagnosis?

Yes. K59.00 may be the principal diagnosis when constipation is the condition established after study to be chiefly responsible for the admission. K59.00 is a secondary diagnosis when another condition accounts for the admission. When fecal impaction complicates the presentation, K56.41 applies instead.

Related codes

Codes in the same family as K59.00. Only codes with a published page render as links.

Sibling codes in the K59.0 family

K59.00: Constipation, unspecified.
K59.01: Slow transit constipation.
K59.02: Outlet dysfunction constipation.
K59.03: Drug induced constipation.
K59.04: Chronic idiopathic constipation, also termed functional constipation.
K59.09: Other constipation.

Additional codes to consider

Codes outside the K59.0 family considered alongside K59.00.

Companion: code alongside when documented

R15.0: Incomplete defecation, an Excludes2 at the K59.0 level, which may be reported with K59.00 when both are independently documented.
K31-: Other diseases of stomach and duodenum, which holds the functional disorders of stomach named in the K59 category Excludes2 note. Concurrent coding is permitted when both conditions are independently documented.

Consider instead

K59.03: Drug induced constipation, when a medication is the documented cause.
K59.04: Chronic idiopathic constipation, the functional constipation code.
K59.01: Slow transit constipation.
K59.02: Outlet dysfunction constipation.
K59.09: Other constipation.
K56.41: Fecal impaction, an Excludes1 with K59.0x, when impaction is documented.
R19.4: Change in bowel habit, for a non-confirmed bowel habit change.
F45.8: Other somatoform disorders, covering psychogenic gastrointestinal disorders, an Excludes1 at the K59 parent level, when a psychogenic etiology is documented.

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