This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
The laboratory diagnosis of thiamine deficiency is by: 
Select and explain. 
A. Transaldolase assay measured before and after the addition of thiamine pyrophosphate, B. Transketolase assay measured before and after the addition of thiamine pyrophosphate, C. Thiamine pyrophosphate assay in RBC after adding sugar, D. Serum LDH levels
B: Transketolase assay measured before and after the addition of thiamine pyrophosphate
Answer: B: Transketolase assay measured before and after the addition of thiamine pyrophosphate 
Explanation: The laboratory diagnosis of thiamine deficiency usually is made by a functional enzymatic assay of transketolase activity measured before and after the addition of thiamine pyrophosphate. >25% stimulation by the addition of thiamine pyrophosphate is interpreted as abnormal. Thiamine or the phosphorylated esters of thiamine in serum or blood also can be measured by high-performance liquid chromatography to detect deficiency.