Proportion of CIN2+ lesions identified and relative sensitivity for women who tested HPV positive at an HC2 RLU/Co ratio of ≥1.
The prevalence of HPV according to the manufacturer's criteria, with a positive RLU/Co ratio of ≥1, was 15.6% (2,860/18,386) for women in the revealed arm at baseline in the ARTISTIC study (Table ). In total, 26% (744/2,860) of the positive samples had an RLU/Co value between 1 and <4, while 74% (2,116/2,860) had an RLU/Co value of ≥4. With increasing severity of the cytology grade, there was a strong linear trend of increasing HPV prevalence, from 10.4% (1,675/16,042) for cytological normality to 43.7% (867/1,986) for borderline/mild dyskaryosis and 88.8% (318/358) for moderate or worse dyskaryosis (PTrend, <0.0001). Histological data were available for 453 women in whom CIN2+ lesions were identified within 30 months of entry into the trial. The proportion of women with HC2 RLU/Co values of ≥1 at baseline for whom CIN2+ was detected was 14.7% (423/2,860). A high proportion of these women (94.8%) had RLU/Co values of >4. The relative sensitivity of the HC2 assay for the detection of CIN2+ was 93.4% (423/453) and increased to 97.0% (226/233) for women who had underlying histologically confirmed CIN3+. In total, 10.5% (23/220) of women with CIN2 lesions were found to be HC2 negative, while only 3% (7/233) of women with CIN3+ lesions were HC2 negative.
Cytology and histology by varying HC2 positivity thresholdsa
Proportion of CIN2+ lesions identified and relative sensitivity for women who tested HPV positive after adjustment of the HC2 RLU/Co value.
Table shows that adjustment of the HC2 positivity threshold to an RLU/Co ratio of ≥2 resulted in a 2.5% (confidence interval [CI], 2.26 to 2.72%) reduction in overall test positivity. The reduction in test positivity at an RLU/Co ratio of ≥2 by cytology grade from that at the lower RLU/Co ratio of ≥1 was statistically significant for women with normal cytology (1,675/16,042 [10.4%] versus 1,286/16,042 [8.0%] positive; reduction, 2.4% [CI, 2.20 to 2.67%]) or borderline/mild cytology (867/1,986 [43.7%] versus 802/1,986 [40.4%] positive; reduction, 3.3% [CI, 2.53 to 4.15%]). There was not a statistically significant reduction for women with moderate/worse cytology (318/358 [88.8%] versus 315/358 [88.0%] positive; reduction, 0.8% [CI, 0.17 to 2.43%]). Adjustment of the HC2 positivity threshold to an RLU/Co ratio of ≥2 would have resulted in a loss of 14 out of 423 (3.3%) CIN2+ lesions (including 4 out of 226 [1.8%] CIN3+ lesions) that were HC2 positive at an RLU/Co ratio of ≥1. This would result in slight decreases in the relative sensitivities for CIN2+ and CIN3+ lesions, to 90.3% (409/453) and 95.3% (222/233), respectively. An increase in the proportion of CIN2+ lesions detected among women who were positive at an RLU/Co ratio of ≥2 over that among women positive at an RLU/Co ratio of ≥1, from 14.7% (423/2,860) to 17.0% (409/2,403), was observed.
If different grades of cytology are compared, among women with normal cytology, an increase in the positivity threshold from an RLU/Co ratio of ≥1 to an RLU/Co ratio of ≥2 would have resulted in 5 out of 32 (15.6%) CIN2+ lesions (including 1 out of 10 [10%] CIN3+ lesions) being missed, with a reduction of 389 out of 1,675 (23.2%) HC2-positive test results (Table ). Among women with borderline/mild cytology, another 6 out of 150 (4%) CIN2+ lesions (including 2 out of 66 [3%] CIN3+ lesions) would have been missed, with the benefit of 65 out of 867 (7.5%) fewer colposcopies if HPV testing was being used for triage.
Increasing the HC2 positivity threshold to an RLU/Co ratio of ≥4 (Table ) results in a further decrease in the overall HPV prevalence to 11.5% (2,116/18,386), equating to 744 fewer HC2-positive test results than would be obtained with a threshold of ≥1, and a reduction in the overall sensitivity for the detection of CIN2+ lesions to 88.5% (401/453). Women with test results at a higher RLU/Co value, ≥4, were at a six-times-greater risk of CIN2+ than women who had an RLU/Co value between 1 and 3.999. The proportions of CIN2+ lesions detected were 19% (401/2,116) and 3.0% (22/744), respectively.
Confirmatory testing of HC2-positive samples by the Roche prototype line blot assay.
Further testing of the 2,860 HC2-positive samples by the Roche prototype LBA found that 35 (1.2%) samples had invalid LBA results, either testing beta-globin negative or having insufficient volume for additional testing. The analytical specificity of HC2-positive samples investigated using the LBA was therefore based on 2,825 samples. The results revealed that at an RLU/Co value of ≥1, 68.3% (1,935/2,825) of the HC2-positive samples were confirmed by the LBA and were found to contain one or more of the 13 HC2 target types (Table ). Significantly more HC2-positive samples were confirmed by the LBA at an HC2 positivity threshold consisting of an RLU/Co ratio between 2 and <4 than at an RLU/Co threshold between 1 and <2 (45.4% versus 22.6%; PTrend, <0.0001). At an RLU/Co threshold of ≥2, 77.2% (1,833/2,374) of HC2-positive samples were confirmed, and at a threshold of ≥4, this proportion increased to 81.5% (1,704/2,090).
Confirmatory testing of HC2-positive samples by the Roche prototype line blot assay
When we examined the proportion of confirmed HC2-positive samples by age group, we found that at an RLU/Co ratio of ≥1, HC2-positive samples were confirmed for 78.7% (1,423/1,807) of 20- to 34-year-olds, while significantly fewer HC2-positive samples (50.3% [512/1,018]) were confirmed for 35- to 64-year-olds (PTrend, <0.0001). Raising the threshold to an RLU/Co ratio of ≥2 increased the proportions of HC2-positive samples confirmed by the LBA to 83.7% (1,355/1,618) for 20- to 34-year-olds and 63.2% (478/756) for 35- to 64-year-olds.
The proportion of confirmed HC2-positive samples is shown to increase with the cytology grade (Table ), from 57.9% (962/1,661) for cytologically normal samples to 96.8% (302/312) for samples showing moderate/severe dyskaryosis (PTrend, <0.0001) at an RLU/Co value of ≥1. Significantly higher proportions of confirmed HC2-positive samples were observed at an RLU/Co ratio of ≥2 than at an RLU/Co ratio of ≥1 for women who had normal cytology (69.1% versus 57.9%; PTrend, <0.0001) or borderline/mild cytology (82.7% versus 78.8%; PTrend, 0.0443). This trend was not apparent among women with moderate/severe dyskaryosis (96.8% versus 96.8%). The risk of CIN2+ lesions during round 1 was significantly higher among women with confirmed HC2-positive samples at an RLU/Co value of ≥1 than among women with unconfirmed samples (95.9% versus 4.1%, respectively).
Table also categorized HC2-positive women who were either positive or negative for HPV 16 and/or 18 DNA by the LBA. As expected, CIN2+ was significantly (P < 0.0001) more prevalent among HPV 16/18-confirmed women than among women with confirmed non-type 16, non-type 18 HPV, irrespective of varying positivity thresholds and across all grades of cytology. The impact of altering the HC2 positivity threshold on the relative sensitivity of detection of CIN2+ lesions was lower for women with confirmed HPV 16 and/or HPV 18.