K59.1 – Functional diarrhea

ICD-10-CM 2027 diagnosis code · Other diseases of intestines

Billable code

ICD-10-CM code K59.1

Code: K59.1 (claims format: K591)
Description: Functional diarrhea
Billable: Yes – valid for HIPAA-covered transactions
Valid for: Dates of service October 1, 2026 – September 30, 2027 (FY2027)
Chapter: 11. Diseases of the digestive system (K00-K95)
Block: K55-K64 Other diseases of intestines
Parent codes: K59

Notes for K59.1

Excludes1 (not coded here):

diarrhea NOS (R19.7)
irritable bowel syndrome with diarrhea (K58.0)

Notes inherited from parent codes

Instructional notes at a category or block level apply to every code below it.

K59 – Other functional intestinal disorders

Excludes1 (not coded here):

change in bowel habit NOS (R19.4)
intestinal malabsorption (K90.-)
psychogenic intestinal disorders (F45.8)

Excludes2 (not included here):

functional disorders of stomach (K31.-)

Index terms for K59.1

Entries in the ICD-10-CM alphabetic index that lead to this code:

Related codes in K59

K59.0 – ConstipationHeader
K59.2 – Neurogenic bowel, not elsewhere classifiedBillable
K59.3 – Megacolon, not elsewhere classifiedHeader
K59.4 – Anal spasmBillable
K59.8 – Other specified functional intestinal disordersHeader
K59.9 – Functional intestinal disorder, unspecifiedBillable

Frequently asked questions

What is ICD-10 code K59.1?

K59.1 is the ICD-10-CM code for functional diarrhea, in the block K55-K64 (Other diseases of intestines).

Is K59.1 a billable code?

Yes. K59.1 is a billable/specific code that can be used to indicate a diagnosis for reimbursement purposes.

What category does K59.1 belong to?

It belongs to category K59 – Other functional intestinal disorders.

Source: CDC/NCHS ICD-10-CM FY2027 code files, tabular list and index. Reference only – code assignment must follow the official ICD-10-CM guidelines and documentation in the medical record.