Patient Reported Outcome (PRO)

A patient reported outcome (PRO) is any report of the status of a patient's health condition or treatment experience that comes directly from the patient, without interpretation by a clinician or anyone else. PROs capture the patient's perspective on symptoms, functional status, quality of life, treatment satisfaction, and other subjective experiences. A PRO is defined by who reports, not by the topic: it is one type of clinical outcome assessment, alongside clinician reported, observer reported (for example, by a parent or caregiver) and performance outcome assessments, which are not PROs because someone else reports or judges the outcome, or the patient performs a defined task.

For decades, clinical research and practice relied primarily on clinician assessed outcomes and biomarkers to evaluate treatments and health status. However, patients' experiences of their own health often diverge from clinical measurements. A treatment that improves laboratory values may not improve how the patient feels or functions in daily life. Conversely, a treatment that produces modest clinical changes may dramatically improve the patient's quality of life. PROs fill this gap by centering the patient's perspective in the assessment of health outcomes. Regulatory agencies including the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA) increasingly recognize PROs as important endpoints in clinical trials, and PRO data have supported drug labeling claims for numerous approved therapies. In clinical practice, systematic collection of PROs can improve communication between patients and providers, identify unrecognized symptoms, and guide treatment decisions.

PROs are collected using standardized questionnaires or instruments that patients complete themselves, either on paper, electronically, or through interviews (though self administration is preferred to minimize interviewer influence). These instruments may be generic, measuring broad aspects of health such as physical functioning, emotional well being, and social participation (examples include the SF 36, EQ 5D, and PROMIS measures), or disease specific, targeting symptoms and functional limitations relevant to a particular condition (examples include the Asthma Quality of Life Questionnaire, the PHQ 9 for depression, and the WOMAC for osteoarthritis).

In the United States, FDA describes a rigorous development process for PRO instruments in its 2009 guidance on PRO measures and, more recently, in its patient focused drug development guidance on fit for purpose clinical outcome assessments, finalized in October 2025. This process includes defining the concept to be measured, generating items based on patient input (typically through qualitative research such as focus groups and cognitive interviews), and evaluating the instrument's psychometric properties including reliability (internal consistency and test retest reliability), validity (content validity, construct validity, and criterion validity), and responsiveness (sensitivity to change).

In clinical trials, PROs can serve as primary endpoints (the main outcome on which the trial's success is judged), secondary endpoints, or exploratory endpoints. When used to support drug labeling claims, the PRO instrument must meet the FDA's standards for adequacy, including evidence that it measures a concept meaningful to patients and that it was developed with patient input. The SPIRIT-PRO extension (2018) guides how PROs are specified in trial protocols, and the CONSORT PRO extension (2013) guides how they are reported in randomized trials.

Electronic PRO (ePRO) collection using tablets, smartphones, or web platforms has become standard in many trials, offering advantages over paper including reduced missing data, time stamped responses, no transcription errors from paper forms, and the ability to implement adaptive testing. Ecological momentary assessment, which collects PRO data multiple times per day in the patient's natural environment, provides a more granular and ecologically valid picture of symptom fluctuation than traditional recall based questionnaires.

Include PROs in clinical trials whenever the treatment is expected to affect how patients feel or function, when the research question involves symptoms or experiences that only the patient can directly assess, or when regulatory agencies recommend PROs for the disease area. In clinical practice, implement systematic PRO collection when patient reported symptoms are important for treatment monitoring and shared decision making. Select PRO instruments based on evidence of reliability, validity, and responsiveness in the target population.

A frequent mistake is using a PRO instrument that was not developed with patient input or validated in the study population, yielding results that may not reflect what matters most to patients. Another error is treating PROs as secondary afterthoughts rather than carefully planned endpoints, leading to poor data quality, missing data, and insufficient statistical power. Researchers sometimes fail to account for missing PRO data, which is often nonrandom (sicker patients are more likely to miss assessments), requiring appropriate analytic methods, such as mixed models (valid when data are missing at random) with sensitivity analyses such as pattern mixture models for data missing not at random. Using a generic instrument when a disease specific one would capture treatment effects more sensitively, or vice versa, is a further consideration. Finally, analyzing individual items rather than validated domain scores can capitalize on chance and produce unreliable findings.

A pharmaceutical company developing a treatment for irritable bowel syndrome includes a validated, disease specific PRO instrument as the primary endpoint in its Phase III trial. The instrument measures abdominal pain severity, bloating, bowel habit satisfaction, and impact on daily activities over the past seven days. Patients complete the questionnaire weekly on a smartphone app. The primary analysis shows that patients in the treatment group report significantly greater improvement in abdominal pain severity (the prespecified primary PRO endpoint) compared to placebo at 12 weeks, supporting the FDA submission for a labeling claim related to symptom improvement.