---
title: "What does a low Vitamin B1 (Thiamine) mean?"
type: biomarker-interpretation
url: "https://www.test-well.com/biomarkers/vitamin-b1-thiamine/low"
biomarker: Vitamin B1 (Thiamine)
direction: low
reference_range:
  - "age 18+: 70.0 – 180 nmol/L"
reviewed_at: 2026-09-08
review_status: reviewed
date_published: 2026-09-05
---

# What does a low Vitamin B1 (Thiamine) mean?

> Low thiamine (vitamin B1) is most common with alcohol use disorder, after bariatric surgery, with persistent vomiting (including pregnancy), diuretic use in heart failure, dialysis, and diets built on refined carbohydrates. Deficiency affects the nerves and the heart — tingling and weakness, and in severe cases confusion and heart failure (beriberi, Wernicke's). It responds quickly to repletion, so a low result is acted on rather than watched.


## When does this result need same-day care?

- Confusion, unsteady walking or abnormal eye movements, especially with alcohol use — emergency care (Wernicke's encephalopathy)

## What is the normal range for Vitamin B1 (Thiamine)?

- age 18+: 70.0 – 180 nmol/L

Can reflect alcohol use, malnutrition, or absorption issues. Severe deficiency causes beriberi.

## What are the common causes of low Vitamin B1 (Thiamine)?

1. Alcohol use disorder
2. Bariatric surgery, malabsorption, prolonged vomiting or diarrhea
3. Loop diuretics (furosemide) in heart failure
4. Dialysis, HIV, hyperthyroidism, critical illness
5. Diets high in refined carbohydrates and low in whole grains, legumes and pork
6. Refeeding after starvation

## What symptoms go with low Vitamin B1 (Thiamine)?

- Tingling, numbness and weakness in the legs, poor balance
- Fatigue, irritability, poor memory
- Swelling, breathlessness, fast heart rate (wet beriberi); confusion and eye-movement problems (Wernicke's) — emergencies

## What do clinicians usually check next?

- Clinician review — deficiency with neurological or cardiac symptoms is treated urgently, before repeat testing
- Magnesium (needed for thiamine to work), B12, folate
- Address the cause: alcohol, absorption, diuretics

Follow-up tests at TestWell: [Magnesium](https://www.test-well.com/tests/magnesium) ($19.99), [Folate (Vitamin B9)](https://www.test-well.com/tests/folate) ($32.99).

## How do you recheck Vitamin B1 (Thiamine)?

| Test or panel | Type | Price | Fasting | Results |
| --- | --- | --- | --- | --- |
| [Vitamin B1 (Thiamine)](https://www.test-well.com/tests/vitamin-b1-thiamine) | Test | $43.99 | Yes | 5–10 business days |

Plus one $6 lab processing fee per order; physician authorization included.

## Common questions

### Which is better, blood thiamine or the erythrocyte transketolase test?

Whole-blood or red-cell thiamine diphosphate (what most labs report) is now the standard; transketolase activity is an older functional test used in some centers.

## Related

- [Vitamin B1 (Thiamine) reference ranges](https://www.test-well.com/biomarkers/vitamin-b1-thiamine)
- [Vitamin D, 25-Hydroxy reference range](https://www.test-well.com/biomarkers/vitamin-d-25-hydroxy)
- [Vitamin B12 reference range](https://www.test-well.com/biomarkers/vitamin-b12)
- [Folate reference range](https://www.test-well.com/biomarkers/folate)

## Sources

- [Mayo Clinic Labs](https://www.mayocliniclabs.com/test-catalog/overview/42356)
- [MedlinePlus (NIH) — Vitamin B Test](https://medlineplus.gov/lab-tests/vitamin-b-test/)

---

Medically reviewed by Youmna DiStefano, MD (Medical Reviewer, TestWell); last reviewed 2026-09-08. Review policy: https://www.test-well.com/editorial-policy

Canonical page: https://www.test-well.com/biomarkers/vitamin-b1-thiamine/low
Machine-readable catalog: https://www.test-well.com/api/catalog.json · MCP server: https://www.test-well.com/mcp · Overview for agents: https://www.test-well.com/llms.txt

Prices are cash-pay, in USD, and include physician authorization; every order adds one flat $6 lab processing fee. Educational content is not a diagnosis — discuss results with a clinician.