Dried Urine Swabs as a Tool for Monitoring Metabolite Excretion

Aim: We tested a large set (n = 181) of wet urine and dried urine samples spotted on regular cosmetic cotton swabs for comparative UHPLC–MS/MS analysis of various metabolites across a wide polarity and structural range. Results/methodology: The agreement of measurements between conventional 24 h urines and dried urine spots made from them in situ was evaluated by Passing–Bablok regression and Bland–Altman analysis after creatinine correction. There was full agreement in qualitative results but quantitative analysis revealed underestimation of dried urine spots in some cases. The dried urine samples contained analytes at measurable levels for at least 9 months. Conclusion: Although this technique seems very promising more methodological studies have to be conducted in order to improve applicability of dried urine microvolume fluidic sampling for quantitative analysis.