(Left) Hematocrit effect: various blood samples containing different hematocrit levels spotted on the same type of paper substrate exhibit different drying properties. (Reprinted with permission from Wilhelm et. al, 2014, copyright 2014 Wilhelm et. al, 2014) (Right) Chromatographic effect: Top: Whole blood spiked with 14C radiolabeled Compound A from Isotope Chemistry and Metabolite Synthesis, sanofi-aventis, spotted on various types of paper substrate storage cards. Bottom: Autoradiogram of 14C distribution in each DBS. (Reprinted with permission from Ren et al., 2010, copyright 2010 Future Science Ltd.)