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
Diagnosis of vitamin B1 deficiency is made by 
Select and explain. 
A. Thiamine level, B. Transketolase activity, C. Carboxylase activity, D. Transaminase activity
B: Transketolase activity
Answer: B: Transketolase activity 
Explanation: Diagnosis of Vit B1 deficiency is made by Transketolase activity.Biochemical Parameters In thiamine deficiency, blood thiamine is reduced, but pyruvate, alpha-ketoglutarate and lactate are increased. Erythrocyte transketolase activity is reduced; this is the earliest manifestation seen even before clinical disturbances.Reference: Textbook of Biochemistry by D M Vasudevan, sixth edition pg no. 392