This research article examines the relationship between infrastructural instability and laboratory work in a public referral hospital in Sierra Leone. Drawing on ethnographic fieldwork conducted inside the hospital’s wards and clinical laboratory, I show how attending to infrastructure and materiality (i.e., laboratory spaces, diagnostic equipment, and supply chains) provides insight into the different kinds of value that laboratory work holds for laboratory technicians, clinicians, hospital administrators, and international donors. Through the case study of a newly arrived non-functioning diagnostic instrument, I reveal the institutional undervaluing of both the laboratory and the improvisation work performed by lab technicians to stabilise unstable equipment. Infrastructural instability in the laboratory enables the generation of new kinds of value, including economic and social value for laboratory technicians themselves, but undermines the clinical value of laboratory tests for clinicians and patients. By discussing the everyday practices, challenges, and meanings of laboratory work in a context of infrastructural instability, I aim to draw attention to the clinical laboratory space as a field site worthy of (more) anthropological inquiry and health systems research and contribute new insights about improvisation, instability, and diagnostic value creation in under-resourced settings.