Sequential Application of Lugol's Iodine Test after Acetic Acid for Detecting Cervical Dysplasia: A Prospective Cohort Study

Applying Lugol's iodine solution to the cervix followed by colposcopic assessment is an established standard test to identify low grade/high grade squamous intraepithelial lesions (LSIL/HSIL). Here, we assessed the performance of Lugol's iodine test during colposcopy using a standardized protocol with 5% acetic acid followed by 5% Lugol's iodine solution and recording the most severe acetowhite (MSAWL) and iodine-negative (MSINL) lesions in a prospective cohort of consecutive women referred to our specialized colposcopy unit. The primary study endpoint was the sensitivity/specificity of MSINL for the detection of LSIL/HSIL. Secondary endpoints were the time to first appearance of the MSINL, MSINL staining intensity, and fading of MSINL. Three hundred and twenty women were included. The sensitivity and specificity of MSINL for the detection of LSIL/HSIL was 81.4 (95%-confidence interval (CI) 77.3-85.0)% and 29.5 (24.2-35.5)%, respectively. Ninety-six MSINL were identified exclusively by Lugol's iodine test (no pathology, n = 46; LSIL, n = 29; HSIL, n = 21) (number needed to biopsy to identify one additional LSIL/HSIL = 1.9). In 17/320 (5.3%) patients, the clinical management was changed based on the result of Lugol's iodine test. Video analysis showed an instant appearance of the MSINL within 10 s in 100% of cases. Intensity of MSINL significantly correlated with the presence/absence of LSIL/HSIL (Spearman rank order correlation; p < 0.0001). Fading of iodine-induced staining intensity over time was not observed. Thus, Lugol's iodine showed moderate sensitivity and poor specificity, but changed clinical management in 5% of cases when used in addition to acetic acid.