OBJECTIVES: The decennial National Surveys of Sexual Attitudes and Lifestyles (Natsal) provide general population prevalence estimates in Britain for key sexually transmitted infections (STIs) through biosampling. Since methodological choices can impact acceptability and response rates, we evaluated processes for Natsal-4, including face-to-face and remote interview arrangements, non-return of test results and vaginal swab collection in two pilot studies. METHODS: The pilots were conducted during June to August 2021 and February to March 2022. Participants aged 16-59 years were invited to provide urine samples (cisgender men and trans/gender diverse) or three vaginal swabs (cisgender women
urine was requested if vaginal swabs were declined) following interview. Samples were self-collected at home and posted to the laboratory by the interviewer if the interview was face to face, or by the participant if they preferred to collect the sample later or the interview was remote. Process feedback was collected after the first pilot via qualitative interviews with participants and after both pilots through informal interviewer debriefing. RESULTS: Of 261 participants interviewed (pilot 1=130
pilot 2=131), 161 (62%) consented to biosampling, of which 129 (49%) provided samples. A sample was received from 78/153 (51%) of women, of whom 60 (77%) provided vaginal swabs and 18 (23%) provided a urine sample. A urine sample was received from 51/108 (47%) cisgender men or trans/gender diverse participants. All samples collected immediately after face-to-face interviews were received (n=77), while 64% of samples from participants consenting to post samples after face-to-face interviews and 60% after remote interviews were received. Process feedback confirmed our methods were broadly acceptable. CONCLUSIONS: We demonstrated that our approach to biosampling and STI testing for a national sexual health survey was reasonably acceptable and feasible in the period coming out the COVID-19 pandemic. Self-collection of vaginal swabs for research, which provide higher testing sensitivity than urine, was feasible and acceptable in a home setting.