The study consisted of two parts. The first was a survey assessing the acceptability of HB-PrEP and the use of the Tasso device for sample collection. The second was to have a subset of participants collect blood samples themselves using the Tasso device and answer questions about their experience. We also compared RPR, HIV antigen/antibody, and creatinine test results from clinician-collected venipuncture specimens and self-collected Tasso specimens.
Participants were patients from Public Health-Seattle & King County (PHSKC) Sexual Health Clinic (SHC) or Max Clinic, both located on the campus of Harborview Medical Center in Seattle, WA, USA. CHS provides comprehensive STI-related medical services and is the largest provider of PrEP in Washington State, with approximately 650 current PrEP patients. Clinique Max is a walk-in clinic for people living with HIV .
Recruitment and registration
The study population included two groups enrolled from May 2020 to February 2021. The first group was recruited online from a subset of current or eligible PrEP users (approximately 75% of all CHS PrEP patients ) who had agreed to receive communications from clinic staff via a secure text messaging platform. At the start of the study and three months after the start, we sent patients a recruitment text containing a brief introduction to the study and a link to complete an online consent form.
The second group included English-speaking patients receiving in-person clinical services at Max Clinic or CHS who had venipuncture specimens taken as part of their routine care. Additionally, patients had to be eligible for or currently using PrEP, have a known or suspected new syphilis infection, or be living with HIV. Since our study began shortly after COVID-19 restrictions dramatically reduced the number of face-to-face visits allowed at University of Washington (UW) and PHSKC facilities, the CHS population was mainly composed of people with symptoms suggestive of STIs. Inclusion criteria for this second group were designed to ensure that the study included people with positive HIV and syphilis tests to allow assessment of concordance between venipuncture and specimens taken. on the Tasso device. People taking anticoagulant medication were excluded from self-sampling. Online consent forms and survey responses were collected and managed using secure web-based tools REDCap (Research Electronic Data Capture)  housed at the UW Institute for Translational Health Sciences. Survey instruments for both groups are available in the appendix (Supplementary Files 1, 2). The study procedures were approved by the University of Washington Human Subjects Division and Institutional Review Board (Study #00009004) and Seattle Public Health Research Administrative Review Board and of King County (Study No. 20-680).
After registration, participants were invited to watch a brief video introducing the Tasso device and the concept of remote PrEP monitoring, and then complete an online survey about their interest in HB-PrEP. Online participants did not receive compensation for their participation in the study.
Group in person
Eligible people were referred to the study by medical providers after completing their clinic visit. After registration, participants viewed a training video  and received detailed instructions on how to obtain blood samples using the Tasso device (Supplementary File 3: Fig. S3). To simulate unsupervised home collection conditions and comply with UW COVID-19 distancing restrictions, study staff were not physically present during self-drawings but remained available as needed for telephone assistance. telephone from the offices adjoining the clinic rooms. The study ordered serum tests on self-collected specimens to match tests ordered at the clinic visit, allowing pairwise comparisons between clinician-collected venipuncture (gold standard) and self-collected Tasso specimens. As such, the number of tests performed for each participant varied (for example, someone attending a routine PrEP follow-up visit at month 15 would typically be tested for HIV and syphilis, but not tested). of creatinine). In the first few months after starting the study, we discovered that using only one Tasso device often resulted in insufficient blood volumes to perform all three tests. Thus, we revised study procedures to instruct all participants to use two devices for sequential collections on the same arm or on different arms. After sample collection, participants completed a survey on the acceptability of self-collected samples and the likelihood of participating in an HB-PrEP program. In cases where collection failed, we attempted to determine probable cause by reviewing collection technique and asking about recent activity in the day prior to collection. All registrants who attempted blood collection and completed a post-intervention survey received a $10 gift card.
Results and Sample Size Considerations
We defined acceptability and feasibility thresholds before the start of the study. Acceptability was defined as ≥85% of participants stating that the device was not difficult to use and that they could consider collecting a sample themselves at home. We defined feasibility as ≥80% of participants successfully collecting samples themselves, without direct supervision, of sufficient volume to perform at least one of the three serum tests for PrEP monitoring.
Given the important clinical implications of misdiagnosing HIV, we determined a priori that matched HIV samples should be 100% concordant. For syphilis test accuracy, we specified that qualitative results would be concordant for ≥75% of cases and that paired quantitative titers would be different by ≤1 dilution, based on the fact that a difference of two titers is usually defined to represent a clinically significant value. cash . We have defined the acceptable range of variation for creatinine samples at ±0.15 mg/dL. Based on data from our CHS PrEP cohorts and previous assessments of capillary vs venous creatinine values that suggest results from venous samples are on average 0.15 mg/dL higher , we hypothesized that the mean creatinine estimates would be 1.1 and 0.95 mg/dL for the venipuncture and Tasso samples, respectively. Thus, we determined that 10 or more paired samples would provide at least 80% power to assess whether the mean difference in creatinine between samples was within a clinically acceptable range.
All sample processing and testing was performed in Clinical Laboratory Improvement Amendments certified facilities. Venipuncture specimens collected by clinicians were tested for HIV, creatinine, and syphilis according to routine CHS protocols. The whole blood samples collected by Tasso were first delivered to the PHSKC laboratory for centrifugation, after which serum was used for testing. Sera were tested for HIV using the GS HIV Combo Antigen/Antibody Enzyme Immunoassay (EIA) (Bio-Rad, Hercules, CA, USA) and for Syphilis using the ASI RPR Card (Arlington Scientific Inc. Springville, UT, USA). All positive RPR tests of Tasso samples were quantitated to a titer of 1:16; values above were determined if the residual volume of the sample allowed it. CAPTIA™ Syphilis IgG EIA (Bio-Rad, Hercules, CA, USA) was used to confirm discordant venipuncture/Tasso RPR samples. HIV and syphilis screening tests were internally validated by the PHSKC laboratory prior to this study. Creatinine testing was performed at the UW laboratory using the Beckman Coulter AU Automated Analyzer (Beckman Coulter Inc., Brea, CA, USA).
We used descriptive statistics to characterize participant demographics, survey responses, and the proportion of participants who attempted and completed self-collections. For HIV and qualitative RPR values, we determined percent positive agreement (PPA) and percent negative agreement (PNA) between venipuncture and self-collected specimen results. We also used descriptive statistics to characterize means, standard deviations, and differences for paired quantitative RPR titers and creatinine values. The correlation between the results of the matched samples was analyzed using Pearson’s correlation coefficients and linear regression. Quantitative RPR titers were plotted on the binary logarithmic scale (eg, the value of 3 represents a titer of 1:8). All analyzes were performed using R version 3.5.1 (R Foundation for Statistical Computing, 2018) and used a two-sided alpha level of 0.05 for statistical significance.