BackgroundIt is suggested that the use of patient reported outcome measure (PROMs) can enhance patients’ consultations with clinicians and improve clinical management. However, existing systematic reviews have found it difficult to reach firm conclusions about the impact of PROMs feedback on the process and outcomes of patient care, largely due to the heterogeneity and complexity of the intervention itself and the wide range of indicators used to assess its impact. This suggests a lack of consensus or even clarity about how this interventions is expected to work.MethodsWe conducted a realist synthesis to explore the contexts in which and processes through which PROMs enable patients to share concerns with clinicians and change clinicians’ communication practices within the consultation. We identified the ideas and assumptions (program theories) underlying how PROMs use was intended to work and developed an overall model to act as a framework for the review. Electronic databases were searched and backwards and forward citation tracking were carried out on key systematic reviews. We selected papers relevant to testing our theories and 36 papers were included.ResultsPROMs completion prompts patients to engage in self-reflection and identify then prioritise issues of importance to them. Whether PROMs supported or constrained patients in sharing issues with clinicians depended on the structure of the PROM and existing clinician-patient relationship. Patients valued PROMs but preferred to share information with clinicians when they had established a trusting relationship with them. Clinicians preferred to develop rapport through their verbal interactions with patients. Clinicians perceived standardised PROMs constrained their relationship with patients and were difficult to incorporate into the flow of consultations. Clinicians avoided using them or adapted the PROM, which may compromise their validity. Individualised PROMs supported consultations by allowing patients to ‘tell their story’ but were less useful as an outcome measure to measure change over time.DiscussionIt is the process of PROMs completion which helps patients to reflect on their health and raise issues with clinicians. The structure of the PROM was a key determinant of the extent to which the use of PROMs supported or constrained the clinician-patient relationship. PROMs may support the care of individual patients through acting as a ‘conversation opener’ rather than as a standardised, quantified summary of patients’ problems.