Thiamine (vitamin B1) deficiency due to degradation, inadequate intake, impaired absorption, or increased metabolic demand remains prevalent in both human and animal populations. In its diphosphate form (thiamine diphosphate, TDP), thiamine serves as an essential cofactor for metabolic enzymes, including transketolase (TKT), a rate-limiting enzyme of the pentose-phosphate pathway. Measurement of TKT activity with and without exogenous TDP provides a functional assessment of thiamine utilization