Methods of quantifying a N2-(1-carboxyethyl)-2′-deoxyguanosine (CEdG) and N2-(1-carboxyethyl)-guanosine (CEG) levels in biological samples and comparing those levels to known normal levels can diagnose a number of metabolic disorders or complications associated therewith, including diabetes, its associated complications, and cancer. Methods can also determine whether therapies for disorders are effective by measuring CEdG and CEG levels before and after treatment. Measurement of CEdG and CEG levels is achieved by using liquid chromatography electrospray ionization tandem mass spectrometry.