– 5′-Deoxyadenosine (5′-dAdo) is an oxidized nucleoside found in the urine of normal subjects. Oxidized nucleosides represent excellent biomarkers for determining the extent of damage in genetic material, which has long been of interest in understanding the mechanism of aging, neurodegenerative diseases, and carcinogenesis. The normal form of deoxyadenosine used in DNA synthesis and repair is 2′-deoxyadenosine where the hydroxyl group (-OH) is at the 2′ position of its ribose sugar moiety. 5′-deoxyadenosine has its hydroxyl group at the 5′ position of the ribose sugar.