Dried Saliva Spot (DSS) as a Convenient and Reliable Sampling for Bioanalysis: An Application for the Diagnosis of Diabetes Mellitus

This paper proposes the dried saliva spot (DSS) as a convenient sampling technique for bioanalysis. The analytical method with the DSS was used for the determination of d,l-lactic acid (d,l-LA) and the d/l ratio of diabetic patients and prediabetic persons for the simple screening of the disease. The d,l-LA in the DSS was labeled with a chiral reagent (DMT-3(S)-Apy) for carboxylic acids and determined by UPLC-ESI-MS/MS. The limits of detection (signal-to-noise ratio (S/N) = 3) for the DSS analysis were on the amol level (∼30 amol). Because good stability, recovery, accuracy, and precision of the d,l-LA for the DSS method was also obtained from the proposed procedure, the DSS method was applied to the determination of the d- and l-isomers of LA of diabetic patients, and prediabetic and healthy persons. The d/l-LA ratio by the present DSS method and the HbA1c value in blood were well-correlated to the serious diabetic patients, whereas the relation in the prediabetic persons was not very good. The reason se...