E51.9 Thiamine deficiency, unspecified

Billable ICD-10-CM code, FY2026. Acts as a Complication or Comorbidity (CC) as a secondary diagnosis.

Applies from E51 Thiamine deficiency

Excludes1 (never code together)

• sequelae of thiamine deficiency (E64.8)

MS-DRG index

Defines the logic of DRG(s) 640-641 in MDC 10.

Approximate ICD-9-CM (GEMs)

• 265.1 Other and unspecified manifestations of thiamine deficiency (approximate)

Code annotations containing back-references to E51.9

Back-references to E51

• Code First: G63 Polyneuropathy in diseases classified elsewhere ("nutritional deficiency (E40-E64)")
• Type 1 Excludes: T45.2X6 Underdosing of vitamins ("vitamin deficiencies (E50-E56)")
• Type 1 Excludes: Z72.4 Inappropriate diet and eating habits ("malnutrition and other nutritional deficiencies (E40-E64)")

Diagnosis Index entries for E51.9

• Aneurin deficiency
• Deficiency, deficient › aneurin
• Deficiency, deficient › thiamin, thiaminic (chloride)
• Deficiency, deficient › vitamin (multiple) NOS › B1 NOS
• Deficiency, deficient › vitamin (multiple) NOS › thiamin
• Thiamin deficiency

Nearby codes

• E51.1 Beriberi
• E51.11 Dry beriberi
• E51.12 Wet beriberi
• E51.2 Wernicke's encephalopathy
• E51.8 Other manifestations of thiamine deficiency
• E51.9 Thiamine deficiency, unspecified (this code)