Disclosed herein are methods, reagent kits, and compositions for performing a bisulfite conversion of DNA directly from a biological sample including a patient's urine sample or a slide-mounted FFPE tissue sample. For example, a method of performing a bisulfite conversion of DNA can comprise certain preliminary steps for processing the biological sample and transferring a portion of the processed sample into a reaction vessel containing a bisulfite mixture. The method can further comprise heating the reaction vessel containing the biological sample and the bisulfite mixture at several heating temperatures and subsequently holding the reaction vessel at a holding temperature for a holding period. The method can also comprise certain bisulfite removal steps, desulfonation steps, and removal of the desulfonation solution. A final elution step can yield the converted DNA for further downstream sequencing and analysis.