Currently, a large scale study is being conducted to verify compatibility of the Xpert®HPV assay (Cepheid) with specimens collected in Surepath Preservative Fluid. Primary aim of this study is to investigate whether both fractions (primary cells and cell pellet) can be considered as suitable input material for the Xpert HPV assay. For this interim analysis, endpoints are limited to results with clinical cutoff only, and matched to corresponding outcomes of the Riatol qPCR genotyping assay as standard comparator test (limited to HR-HPV types only).
In total, 100 samples were prospectively collected and processed according to the standard Surepath method for cytology. Two different cell fractions were obtained per sample, i.e. left-over primary sample and pelleted cells after gradient purification. Both cell fractions are stored at 4°C, and further processed on both the Xpert HPV assay and the Riatol qPCR genotyping assay. Clinical thresholds were applied accordingly during this analysis. Paired T-test was used to compare Ct-values of both fractions.
Median age of study participants was 46 years (IQR = 31 – 56). The first 100 samples gave valid results for 96 paired samples on Xpert HPV. HPV prevalence in this subset was 27/96 (28.1%). In all tested sample pairs, no clinical difference was observed between primary sample and pelleted cells. When comparing Ct-values for HMBS (cell adequacy control), significantly higher HMBS signals were found in the primary sample versus the processed fraction (p <0,001), indicating less cells in this fraction. At clinical level, full concordance between the standard comparator test (Riatol qPCR genotyping assay) and the Xpert HPV assay was observed. Errors (4 errors/200 reactions; 2%), were observed both in primary sample fraction (n=3) and in pelleted cells (n=1).
This interim analysis indicates a good compatibility of the Xpert HPV assay with samples collected in Surepath Preservative Fluid. Both cell fractions, generated after standard Surepath processing, can be analyzed without pre-treatment on the Xpert HPV assay. Results are shown to be clinically valid, as no differences could be observed with a validated comparator assay (Riatol qPCR genotyping assay). Higher concentration of cells was measured in the pelleted fraction, however these preliminary results do not indicate influence at clinical level, as no discordant HPV results between both Surepath cell fractions could be observed.