Reporting Guidelines for Single-Arm Interventional Studies
For single-arm interventional trials, there is no dedicated reporting guideline equivalent to CONSORT for randomized trials; however, authors should adapt relevant elements from CONSORT 2010/2025 and ensure comprehensive reporting of trial design, methods, outcomes, and results with particular attention to justifying the single-arm design and addressing inherent limitations.
Core Reporting Framework
While the CONSORT statement specifically addresses randomized controlled trials 1, 2, 3, single-arm interventional studies should adapt applicable CONSORT elements to maximize transparency and utility. The absence of a control group does not eliminate the need for rigorous reporting standards.
Essential Components to Report
Title and Abstract:
- Clearly identify the study as a single-arm interventional trial in the title
- Provide a structured summary including trial design, methods, results, and conclusions 1
Introduction:
- Justify why a single-arm design was chosen rather than a randomized trial—this is critical and often overlooked 4
- Provide scientific background and rationale for the intervention
- State specific objectives or hypotheses 1
Methods Section:
Trial Design:
- Explicitly describe the single-arm design and acknowledge the absence of randomization
- Document any important changes to methods after trial commencement with reasons 1
Participants:
- Define eligibility criteria with precision
- Specify settings and locations where data were collected
- Report recruitment dates and follow-up periods 1
Interventions:
- Describe the intervention with sufficient detail to allow replication, including how and when it was actually administered 1
- Consider using the TIDieR (Template for Intervention Description and Replication) checklist for comprehensive intervention reporting 5
Outcomes:
- Completely define all pre-specified primary and secondary outcome measures, including how and when they were assessed 6
- Justify the target effect size or threshold for clinical meaningfulness used in sample size calculations 6
- Document any changes to outcomes after trial commencement with reasons 1
Sample Size:
- Explain how sample size was determined, including assumptions about expected effect size
- For certain contexts (e.g., BCG-unresponsive bladder cancer), specific thresholds exist: a clinically meaningful initial complete response rate of at least 50% at 6 months, 30% at 12 months, and 25% at 18 months 7
Statistical Methods:
- Describe statistical methods used for outcome analysis
- Acknowledge limitations inherent to single-arm designs, particularly the inability to control for confounding and temporal trends 4
Results Section:
Participant Flow:
- Report numbers of participants who were enrolled, received intended treatment, and were analyzed for the primary outcome
- Document losses and exclusions after enrollment with reasons 1
- Use a flow diagram adapted from CONSORT 2
Baseline Data:
- Present a table showing baseline demographic and clinical characteristics 1
Outcomes:
- For each primary and secondary outcome, report results with estimated effect size and precision (such as 95% confidence interval) 1
- Report both absolute numbers and proportions for binary outcomes 6
Harms:
- Report all important harms or unintended effects, including deaths, serious adverse events, and events leading to discontinuation 8
- Specify timing, frequency, and duration of adverse events 8
Discussion Section:
Limitations:
- Explicitly address the absence of a control group and implications for causal inference 4
- Discuss sources of potential bias, particularly selection bias and confounding
- Address the limited certainty of evidence from single-arm designs 4
Generalizability:
- Discuss external validity and applicability of findings
- Acknowledge that single-arm trials typically have limited generalizability compared to randomized trials 9
Interpretation:
- Interpret results cautiously, balancing benefits and harms
- Consider other relevant evidence, particularly from comparative studies 1
Other Information:
- Provide trial registration number and registry name
- Indicate where the full trial protocol can be accessed
- Disclose funding sources and role of funders 1
Context-Specific Considerations
When Single-Arm Designs May Be Appropriate:
Single-arm trials are most justified in specific circumstances 10:
- Rare diseases where randomization is not feasible
- Emerging infectious diseases requiring rapid evidence
- Situations where equipoise does not exist
- Early-phase evaluation of novel interventions
- When historical controls or real-world data can provide context 9
Critical Pitfall to Avoid:
The most common deficiency in single-arm trial reporting is failure to justify the design choice and adequately address the resulting limitations 4. Authors must explicitly state why a randomized design was not feasible or ethical, and acknowledge that the absence of concurrent controls limits causal inference.
Emerging Approaches
Recent methodological developments suggest that single-arm trials can be strengthened through:
- Random invitation designs (RISAT) where participants are randomly selected from a registry or database to receive intervention invitations, with outcomes compared to non-invited individuals using real-world data 9
- Integration with prospective registries or cohort studies to provide comparative context 4
- Protocol-driven approaches adhering to PRISMA guidance for systematic integration of results 4
Practical Implementation
For journal submission:
- Complete a modified CONSORT checklist indicating where each applicable item is addressed
- Provide page numbers for each reported element
- Consider using the CONSORT 2025 expanded checklist format with bullet points for critical elements 3
Quality indicators: Studies with better intervention reporting tend to be preregistered 5, suggesting that prospective registration improves reporting completeness even for single-arm designs.