This work intends to identify and follow up quality control parameters important for the general improvement of our thermoluminescence dosemeter (TLD) system for Individual Monitoring that is currently preparing its accreditation according to the EN ISO/IEC 17025 Standard. A retrospective analysis of the readers' start-up tests revealed an eventual variation of parameters, like the high voltage, which may affect the light collecting system, and hence the TL dose results. This was investigated and although the high voltage requires a careful look, the stability and reproducibility of the TLD system was ascertained by the results of quality control procedures. As a consequence of this work, the start-up procedure was modified and the warning levels used for the start-up daily tests of the readers were derived from a more realistic approach.