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15-11-2011 | Gynaecology | Article

Analytical performance for cobas and hybrid capture 2 HPV tests


Free abstract

MedWire News: The cobas human papillomavirus (HPV) test is similar to the hybrid capture 2 (HC2) test in terms of detecting high-risk (hr) genotypes, but has a lower rate of cross-reactivity with low-risk (lr) genotypes, researchers report.

The findings arise from the cobas Early Evaluator Program, which compared the analytical and clinical performance of the Roche cobas HPV test with that of the current standard of HPV DNA testing, the Digene HC2 HPV DNA test.

Maria Mateos (Hospital Ramón y Cajal, Madrid, Spain) and colleagues explain that HPV is a causal agent of cervical cancer, and persistent HPV16 or HPV18 infection carries a particularly high risk.

The cobas test provides individual HPV16 and HPV18 genotyping results plus a combined result for 12 other hr HPV genotypes, while the HC2 test simultaneously detects 13 hrHPV genotypes including HPV16 and HPV18.

The analytical performance of the cobas test for hrHPV genotype detection was compared with that of the HC2 test in cervical samples collected from 1360 women attending routine cervical cancer screening or follow-up of Pap smear abnormalities in three European centers.

The researchers report that the HC2 test identified 638 samples as hrHPV positive, 709 as hrHPV negative, and 13 as indeterminate. The cobas test identified 632 samples as hrHPV positive, 728 as hrHPV negative, and none as indeterminate.

The concordance between the two tests was 86.6%, while the percentages of positive and negative agreement were 86.2% and 90.0%, respectively.

All discordant samples were then analyzed with the linear array (LA) HPV genotyping test.

This test detected lrHPV genotypes in 58% (52/90) of HC2-positive/cobas-negative samples, and in 14% (7/50) of HC2-negative/cobas-positive samples.

Conversely, more hrHPV genotypes were detected in HC2-negative/cobas-positive samples compared with HC2-positive/cobas-negative samples. Specifically, the LA HPV test detected hrHPV genotypes in 16% (14/86) of HC2-positive/cobas-negative samples and in 48% (24/50) of HC2-negative/cobas-positive samples.

Further analysis revealed that the associations between HC2-positive/cobas-negative samples and a lrHPV-positive LA HPV test result, and between HC2-negative/cobas-positive samples and a hrHPV-positive LA HPV test were statistically significant.

These findings suggest that the HC2 test has greater cross-reactivity with lrHPV genotypes than does the cobas test, and that the HC2 test misses more hrHPV genotypes than the cobas test, Mateos and co-authors remark in the Journal of Molecular Diagnostics.

Even so, the high degree of concordance observed between the two tests indicates that they perform similarly for the detection of hrHPV genotypes, they add.

The researchers note that, for the purpose of this comparison, the hrHPV genotype status of each sample was provided as a pooled result by both tests, but the cobas test is also able to distinguish individual HPV16 and HPV18 genotypes if required.

"Therefore, the additional HPV16/18 genotyping information offered by the cobas HPV test may further help guide patient management in conjunction with the physician's assessment of cytology history, other risk factors, and professional guidelines," they conclude.

By Laura Dean

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