In this paper we will consider the usage of knowledge modelling and design with conceptual design and analysis in improving the knowledge description of medical data. There exists many XML and information system (IS) based approaches for producing easy to use, reliable, trustworthy and coherent medical systems and services, like the concepts of HL7. In computer applications web, web services and semantic web based technologies and tools are being used in the business and ecommerce scenarios to produce user-focused, (business) process oriented services in future medical IS. Our case is focused on laboratory exams and their knowledge analysis for predicting and analyzing the usage of various drugs by patients. We show with our case the role of semantic knowledge modelling in coordinating various medical services in a real hospital setting, and hope to extend our work in the future towards semantic web based applications that improve and ease the patient treatments in the IS of the future hospitals.