How to Check Thiamine Level
The most reliable method to assess thiamine status is measuring red blood cell (RBC) or whole blood thiamine diphosphate (ThDP) using HPLC, not plasma thiamine, as virtually all circulating ThDP is in erythrocytes. 1
Recommended Laboratory Test
Measure RBC or whole blood thiamine diphosphate (ThDP) as the preferred biomarker for thiamine status assessment. 1, 2
Why This Test is Superior
- Plasma measurement is not useful since virtually all circulating ThDP is in the erythrocytes, making plasma levels unreliable. 1
- RBC ThDP is unaffected by inflammation, making it the most reliable marker in critically ill patients or those with systemic inflammatory responses. 1
- ThDP represents approximately 80% of total body thiamine stores and is the active coenzyme form. 3
Alternative Testing Methods
Erythrocyte Transketolase Activity (Functional Assay)
This indirect method measures ThDP-saturation of thiamine-dependent enzymes via the pentose phosphate pathway. 1
Limitations of this approach:
- May not be readily available in most clinical laboratories. 1
- Results can be difficult to interpret when transketolase synthesis is impaired (e.g., liver disease, critical illness). 1
- Less reliable than direct ThDP measurement in acute clinical settings. 1
Analytical Methodology
High-pressure liquid chromatography (HPLC) coupled to optical or mass spectrometry detection is the standard analytical method for determining ThDP. 1, 4, 5
Sample Collection Requirements
Critical pre-analytical considerations must be followed: 1
- Protect samples from light during collection and storage
- Maintain proper temperature storage to ensure reliable results
- Use whole blood or packed erythrocytes, never plasma alone 1
Reference Ranges
- Erythrocyte TDP: 280-590 ng/g hemoglobin 5
- Whole blood TDP: 275-675 ng/g hemoglobin 5
- Total thiamine in whole blood: 75-194 nmol/L (mean 125 nmol/L) 4
Critical Clinical Caveat: Don't Wait for Results
Treatment should NOT be delayed while waiting for laboratory confirmation. 1, 2
Why Empiric Treatment is Essential
- Thiamine reserves can be depleted within 20 days of inadequate oral intake. 1, 2
- Irreversible neurological damage (Wernicke's encephalopathy) can occur within days if untreated. 1
- A therapeutic trial of thiamine supplementation should be performed immediately to assess clinical benefit in suspected deficiency. 1
- Thiamine has no established upper toxicity limit, making empiric treatment extremely safe. 2
Supportive Biomarkers of Deficiency
When thiamine deficiency is suspected, additional metabolic markers can support the diagnosis: 1
- Elevated lactate (thiamine deficiency causes type B lactic acidosis)
- Elevated pyruvate
- Elevated alpha-ketoglutarate
- Elevated glyoxylate
These markers reflect impaired glucose metabolism due to thiamine-dependent enzyme dysfunction but are not specific for thiamine deficiency. 1
Emerging Sampling Methods
Dried Blood Spot (DBS) and Volumetric Absorptive Microsampling (VAMS)
Recent research demonstrates that finger-prick capillary blood collected on VAMS devices provides results comparable to venous whole blood sampling. 6, 7
Advantages of microsampling:
- Requires only one drop of finger-prick blood 6
- Samples can be safely transported through regular mail without affecting results 6
- Stable at -20°C for up to 42 days 7
- Particularly useful for epidemiological studies in remote or resource-limited settings 6
These methods show excellent agreement (94-100% of results within 20% of venous samples) with no significant bias. 6
High-Risk Populations Requiring Testing
Consider measuring thiamine levels in: 2
- Patients with cardiomyopathy on prolonged diuretic treatment (6% prevalence of deficiency)
- Critically ill patients (>90% have deficiency or depletion)
- Alcohol use disorder (30-80% show deficiency)
- Post-bariatric surgery patients, especially first 3-4 months postoperatively
- Patients with unexplained encephalopathy, confusion, or neurological symptoms
- Those receiving prolonged parenteral nutrition
- Patients at risk for refeeding syndrome