The Capital Region of Denmark is currently implementing HPV self-sampling to screening non-attenders as a new offer in the organized screening program. From the pilot implementation study, offering 24,000 non-attenders an Evalyn self-sampling brush (Rovers, Oss, Netherlands), we have previously described that only 0.3% of the returned brushes returned an invalid result upon HPV testing using the BD Onclarity HPV assay. However, temperatures differences across a calendar year, prolonged storage after sampling or during transport in the mail from the woman to the lab could potentially affect the analytical stability of the dry, self-taken samples. To strengthen the evidence for use of self-sampling, we investigated the analytical stability of the Evalyn dry brush for HPV testing as a function of time and ambient temperatures.
To simulate self-taken samples, we used residual cervical swabs (Copan Universal Transport Media, SSI, Copenhagen) from Danish women undergoing routine diagnostic HPV testing at Copenhagen University Hospital. Brushes were dipped in residual media, left to dry and then stored at three different temperatures (room temperature, 4°C and 30°C) prior to being analyzed using the clinically validated BD Onclarity HPV assay at four different storage time points, T=0 (baseline), 2, 4, and 8 weeks. Analytical quality of the samples was assessed using the Ct value on the BD Onclarity HPV test internal control Human Beta Globin Control (HBB). Up to four brushes were derived from each swab sample, allowing for longitudinally comparison of different study points. After storage and prior to Onclarity testing, the brush heads were removed and rinsed in 3 ml BD CBD medium. 1.0 ml was used for HPV testing in concordance with manufactures specifications.
The mean Ct value of the HBB outcome per sample was compared. No statistical difference was observed in HBB Ct values between baseline and T=2 weeks, 4, and 8 weeks regardless of storage temperature (4°C; p=0.951, Room temperature; p=0.763, 30°C; p=0.203). All samples were reproducible with respect to HPV result and the Ct values of the individual HPV genotype groups were stable throughout the time points.
This data conclusively shows that dry brushes used for HPV self-sampling are analytically stable with respect to human and HPV DNA up to 8 weeks after the actual sampling, as well as over temperature conditions ranging from 4C to 30C. This provides important data for implementation of HPV self-sampling worldwide under different temperature and environment conditions.