Abstract: Methods for determining a variant frequency in a test sample from a subject, and methods for labeling sequencing reads as having or not having a variant are described herein. Exemplary methods include generating a reference match score and a variant match score by aligning sequencing reads to a corresponding variant sequence and a corresponding reference sequence, and labeling the sequencing read as having or not having the variant based on the determined match scores. Also described herein are methods monitoring disease progression and methods of treating a subject having a disease. Further described are devices and systems for implementing such methods.