ICD-10 Code E51.9 – Thiamine deficiency, unspecified (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code E51.9 – Thiamine deficiency, unspecified
What it is
E51.9 identifies thiamine (vitamin B1) deficiency when the record does not specify a more exact form. Use it for documented deficiency of thiamine without a named syndrome or cause.
Clinical signs
Clinical features vary; refer to documentation. Commonly reported findings include poor nutrition, weakness, fatigue, neuropathic symptoms, or neurologic changes consistent with thiamine deficiency.
When to use this code
Use this code when the provider documents thiamine deficiency but does not name a specific related condition such as beriberi or Wernicke encephalopathy. It also fits when the chart confirms deficiency, yet the type or cause is not further defined. Check documentation if a more specific diagnosis is available.
Do not use for
Do not use E51.9 when the record supports a more specific thiamine-related diagnosis, such as a defined deficiency syndrome. Do not assign it for suspected deficiency without documentation.
Coding tip
Query the provider if the note suggests a specific thiamine deficiency manifestation, because a more precise code may be available.