The main goal of this paper is to show the usefulness of the logic-combinatory approach in pattern recognition theory for developing auxiliary criteria for differential medical diagnosis, based on the methodology presented by Heathfield et al. (J Biomed Eng 13 (1991) 51-57). Firstly, we propose a change in the characterization base, from disease characterization to patient characterization then, we suggest a k-valued treatment for variables which allows us to assign them values in a wider range in order to represent different degrees in symptom manifestations. Secondly, the methodology proposed is based on Testor Theory. This theory allows us to obtain the minimum combination of features (symptoms) and the set of features combination equally discriminant (typical testors) among the diseases considered. Then, applying some classification algorithm that uses typical testors, physicians will have more making differential flexibility diagnosis.