This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: vitamins, Subject name: Biochemistry
Investigation of choice in Thiamine deficiency is 
Select and explain. 
A. RBC-Thiamine levels, B. RBC - Transketolase levels, C. RBC - Glutathione reductase levels, D. WBC - Ascorbic acid levels
B: RBC - Transketolase levels
Answer: B: RBC - Transketolase levels 
Explanation: Severe thiamine deficiency is associated with: Decreased RBC transketolase activity this is the earliest manifestation seen even before clinical disturbances Thiamin is a cofactor of Transketolase pyruvate, alpha-ketoglutarate and lactate level in blood increases in thiamine deficiency ref: DM Vasudevan 8th ed page 467