Performance of the acetic acid test when used in field conditions as a screening test for cervical cancer.
De, Vuyst H
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OBJECTIVE: To assess if visual inspection with acetic acid (VIA) is a useful alternative screening test for cervical cancer, when used in a resource-poor setting with an existing cytology-based screening programme. METHODS: Women living in Rivas district (Nicaragua), who attended the programme, were concurrently screened with VIA and Papanicolau (PAP) smear. Screening was performed by health providers who had received training in VIA and a refresher course in cytology. Women testing positive for either of the results were referred for colposcopy and biopsy when indicated. The performance of VIA was compared with PAP smear, calculating the relative true and false positive rate (RELTPR and RELFPR) and for a high threshold on biopsy (cervical intraepithelial neoplasia grade 2 or a higher grade). We determined the trade-off between both tests by calculating the ratio of extra false positives detected through extra true positives (EFP:ETP ratio). RESULTS: A total of 1076 patients were screened. Nearly 33% had a positive screening test. On biopsy, 7.6% had a low-grade intraepithelial lesion, 4.5% a high-grade intraepithelial lesion (HSIL) and 0.5% invasive cancer. The RELTPR (VIA to PAP) was 1.96, the RELFPR 5.02 and the EFP:ETP ratio 8.04. VIA detected twice as much HSIL and invasive cancers as the PAP smear. Yet, for every extra diagnosis, eight extra false positives had to be examined at the referral level. CONCLUSIONS: The VIA spectacularly increases the number of HSIL and invasive cancers detected. The high FPR is a concern for the organization of the referral level. There is a need to establish uniform criteria on test positivity and to further improve the performance in field conditions.