It has been argued that medical technologies do more than simply generate representations of reality. Like other technologies they act on the situations in which they are used. This article is based on ethnographic fieldwork carried out among young adults with type 1 diabetes in Oslo, Norway. An important test in the treatment of type 1 diabetes, the glucosylated haemoglobin test (HbA1c), is discussed as a technology, as a theme in the clinical dialogue, and as a component of the self-management regime. The test gives an estimate of average blood sugar levels and thus serves to represent the quality of the patient's everyday self-management. In the light of the ethics of responsibility established by self-management as a treatment regime, we suggest that the HbA1c test can assume the function of a sign indicating moral qualities in the patient, and that this has an impact on the clinical dialogue. This test-as-sign offers an illustration of how bioscience technologies may enter into people's understanding of themselves in what has been termed a "risk society".