Changing from cytology to HPV testing as the primary screening analysis in organized programs for Cervical Cancer Screening will increase the requirements for bio-banking of cervical screening samples with respect to audit and quality assurance. The quality of stored, extracted DNA is well documented but what about storage of original sample material? The cervical cancer screening in Denmark is predominantly conducted using SurePath (BD, Sparks, Maryland, US) for sample collection. Here we present data on the analytical stability of SurePath collected cervical samples for HPV testing with ≥7 months storage of original SurePath samples between baseline testing and re-test.
We collected 1216 samples (897 NILM and 319 ≥ASCUS samples) from Danish women undergoing routine screening in the Capital Region of Denmark. The samples were split into two aliquots. Aliquots were tested at base line and after ≥7 months (4°C) using the clinical validated Onclarity HPV assay (BD, Sparks, Maryland, US). Stability of the SurePath samples were assessed by 1) clinical reproducibility of results between 1st and 2nd test, 2) analytical quality assessment using the mean Ct-value of the internal control (HBB) of the Onclarity assay as a proxy-marker of overall DNA quality after storage, and 3) HPV genotype specific Ct-values of positive samples were used to address the stability of HPV DNA. The mean Ct-values of the internal HBB control and the HPV positive results were compared using the one-way ANOVA test (SPSS version 22).
The overall reproducibility (positive-positive and negative-negative) was 98.0% (N=1192) with 1.8% (N=24) being discordant. No significant difference in the mean Ct-values of the internal HBB control (HBB; p=0.667) between the baseline test and the 2nd test were observed. The discordant samples were Ct 32.1±1.4 versus the manufacturer defined cut off of Ct 34.2. Furthermore, no significant difference were observed in measured Ct-values of the individual HPV genotypes detected between baseline and 2nd test; HPV16; p= 0.773, HPV18; p=0.530, HPV31; p=0.701, HPV33/58; p=0.996, HPV35/39/68; p=0.923; HPV45; p=0.992, HPV51; p=0.722, HPV 52; p=0.896, HPV56/59/66; p=0.626.
In conclusion, SurePath collected cervical screening samples can be stored at 4°C for at least 7 months without significant deterioration of the clinical or analytical quality of the material with respect to HPV testing when using the Onclarity HPV assay.