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
Test to diagnose thiamine deficiency - 
Select and explain. 
A. RBC transketolase, B. FIGLU excretion, C. Methyl-malunic acid in urine, D. Histidine load test
A: RBC transketolase
Answer: A: RBC transketolase 
Explanation: Ans. is 'a' i.e., RBC transketolase o Thiamine diphosphate is also the coenzume for transketolase, in the pentose phosphate pathway. Therefore, thiamine nutritional status is best assessed by erythrocyte (preferred) or whole blood transketolase activity.