K59.1 Functional diarrhea

Billable ICD-10-CM code, FY2026.

Excludes1 (never code together)

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

Applies from K59 Other functional intestinal disorders

Excludes1 (never code together)

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

Excludes2 (not included here)

• functional disorders of stomach (K31.-)

MS-DRG index

Defines the logic of DRG(s) 391-392 in MDC 06.

Approximate ICD-9-CM (GEMs)

• 564.5 Functional diarrhea

Code annotations containing back-references to K59.1

Back-references to K59.1

• Type 1 Excludes: K52.9 Noninfective gastroenteritis and colitis, unspecified ("functional diarrhea (K59.1)")
• Type 1 Excludes: R19.4 Change in bowel habit ("functional diarrhea (K59.1)")
• Type 1 Excludes: R19.7 Diarrhea, unspecified ("functional diarrhea (K59.1)")

Diagnosis Index entries for K59.1

• Diarrhea, diarrheal (disease) (infantile) (inflammatory) › functional
• Diarrhea, diarrheal (disease) (infantile) (inflammatory) › neurogenic

Nearby codes

• K59.01 Slow transit constipation
• K59.02 Outlet dysfunction constipation
• K59.03 Drug induced constipation
• K59.04 Chronic idiopathic constipation
• K59.09 Other constipation
• K59.1 Functional diarrhea (this code)
• K59.2 Neurogenic bowel, not elsewhere classified
• K59.3 Megacolon, not elsewhere classified
• K59.31 Toxic megacolon
• K59.39 Other megacolon
• K59.4 Anal spasm