Thiamine (vitamin B1) is an essential B vitamin required for carbohydrate metabolism and normal neurologic function. It serves as a precursor to thiamine pyrophosphate (TPP), also known as thiamine diphosphate (TDP), the active coenzyme form involved in key metabolic pathways including glycolysis, the citric acid cycle, and the pentose phosphate pathway.

Deficiency of thiamine can result in severe clinical syndromes such as beriberi and Wernicke–Korsakoff syndrome, most commonly associated with chronic alcoholism, malnutrition, or malabsorption. However, subclinical deficiency is frequently underdiagnosed using serum thiamine levels alone, which poorly reflect tissue stores.

The ETKAC assay evaluates functional thiamine status by measuring the activity of erythrocyte transketolase (ETK), a TPP-dependent enzyme in red blood cells. Because most TPP is intracellular, ETK activity provides a more accurate assessment of tissue thiamine sufficiency than plasma vitamin levels. The assay measures:

• Basal transketolase activity
• TPP-stimulated activity
• Activity coefficient (ETKAC = stimulated / basal activity)

These combined metrics help determine whether functional deficiency is due to reduced vitamin availability, impaired enzyme activity, or both.

• Preferred: Refrigerated (2–8°C)
• Same-day processing at room temperature acceptable

Gross hemolysis or delayed transport beyond stability limits

• ≤48 hours refrigerated: acceptable for all parameters
• 48–72 hours refrigerated: basal activity may decrease up to 6.7%
• 72 hours or >24 hours at room temperature: specimen unacceptable

Notes

Fasting not required but recommended; avoid non-essential medications ≥24 hours prior if possible

Special Chemistry enzymatic assay using UV-Vis spectrophotometry (340 nm) to measure erythrocyte transketolase activity rates with and without TPP activation.

Normal: ETKAC within reference range consistent with adequate thiamine-dependent enzyme function.

Functional Thiamine Deficiency: Elevated ETKAC indicates reduced transketolase activation consistent with thiamine deficiency or impaired utilization.

High-Risk Deficiency: ETKAC >1.25 suggests significant functional thiamine deficiency.

Low Basal Activity (<0.59 U/gHb): Suggests reduced enzyme capacity and possible severe deficiency; interpret with ETKAC.

Overall Interpretation: ETKAC reflects functional thiamine status; basal activity provides supporting information on enzyme function and helps distinguish cause of deficiency.

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• Clinical Immunology Laboratory validation data and internal reference range study.

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