Are thiamine levels useful in clinical practice?

Thiamine Levels in Clinical Practice: Utility and Applications

Thiamine levels are useful in specific clinical scenarios but should not be routinely measured in all patients. Measurement of RBC or whole blood thiamine diphosphate (ThDP) is recommended only for patients with suspected deficiency in high-risk contexts such as cardiomyopathy with prolonged diuretic treatment, prolonged medical nutrition, post-bariatric surgery, refeeding syndrome, and encephalopathy. 1

When to Measure Thiamine Levels

Thiamine levels should be measured in:

• Patients with suspected deficiency in the context of cardiomyopathy and prolonged diuretic treatment 1
• Patients undergoing nutritional assessment during prolonged medical nutrition and post-bariatric surgery 1
• Patients with refeeding syndrome 1
• Patients with encephalopathy of uncertain etiology 1
• Patients with kidney failure receiving kidney replacement therapy (KRT) due to increased losses 1
• Patients with suspected thiamine deficiency presenting with neurological symptoms, unexplained heart failure, or lactic acidosis 1, 2

How to Measure Thiamine Status

• RBC or whole blood thiamine diphosphate (ThDP) is the recommended measurement method (Grade A recommendation) 1
• Plasma measurement is not useful since virtually all circulating ThDP is in erythrocytes 1
• If RBC or whole blood ThDP determination is unavailable, measurement of red cell transketolase activity and its activation by thiamine may be considered 1
• Special sample collection procedures are required (protection from light, temperature storage) 1

Clinical Significance of Thiamine Deficiency

Thiamine deficiency can present with:

• Neurological symptoms: apathy, decreased short-term memory, confusion, irritability, cognitive deficits, Wernicke-Korsakoff encephalopathy, optic neuropathy 1
• Cardiovascular manifestations: beriberi, congestive heart failure 1, 2
• Metabolic derangements: unexplained lactic acidosis 1, 2
• Refeeding syndrome, which is associated with increased mortality 1

High-Risk Populations

Thiamine levels are particularly useful in monitoring:

• Patients with malnutrition, poor oral intake, and chronic alcohol consumption 1
• Patients with malignancies and increased metabolic requirements 1
• Patients with reduced gastrointestinal absorption due to disease or surgery 1
• Patients on chronic diuretic therapy or continuous renal replacement therapy 1
• Pre- and post-bariatric surgery patients 1
• Patients with heart failure (deficiency found in 6% of ambulatory patients) 1
• Critically ill patients (deficiency or depletion found in >90% of patients) 1, 3
• Patients with hepatic encephalopathy (to differentiate from Wernicke's encephalopathy) 1

Treatment Based on Thiamine Levels

When thiamine deficiency is detected:

• Mild deficiency (outpatients): 10 mg/day thiamine for a week, followed by 3-5 mg/day for at least 6 weeks 1
• High suspicion or proven deficiency: 200 mg, 3 times a day, IV 1
• Encephalopathy of uncertain etiology: 500 mg, 3 times a day, IV 1
• Maintenance dose after proven deficiency: 50-100 mg/day, orally 1
• Refeeding syndrome: 300 mg IV before initiating nutrition therapy, 200-300 mg IV daily for at least 3 more days 1

Limitations and Considerations

• Thiamine reserves can be depleted as early as 20 days of inadequate oral intake 1
• Treatment should not be delayed by waiting for laboratory results; a thiamine supplementation trial should be performed to assess clinical benefit 1
• Unlike other vitamins, red cell ThDP is not affected by inflammation, making it a reliable marker even in patients with inflammatory conditions 1
• Thiamine has no established upper limit for toxicity, with excess being excreted in urine 1
• High IV doses rarely lead to anaphylaxis, while doses exceeding 400 mg may induce mild side effects such as nausea, anorexia, and mild ataxia 1

In conclusion, while thiamine levels are not universally useful for all patients, they provide valuable clinical information in specific high-risk populations and should be incorporated into the diagnostic workup of patients with suspected deficiency or those at high risk of developing deficiency.