Repeat Processing of Residual ThinPrep Pap Tests: Sampling of the Vial May Not Be Invariably Homogeneous

Objective: To re-evaluate the reproducibility of additional slides prepared from residual cervical ThinPrep (TP) samples. Study Design: Sixty paired specimens (conventional smears and direct-to-vial TP) were studied. Up to 10 additional slides were prepared from each TP vial. All slides were reviewed for adequacy of material, presence of abnormal cells and presence of normal flora or other pathogens. The additional TP slides were further evaluated for the presence of diagnostic elements which were not found on the conventional smear and primary TP slide. Results: Abnormal cells found on the primary TP slide were also identified on all additional slides in 48/50 cases (96%) with squamous cell lesions. The distribution of material on TP slides was evaluated as homogenous in 51 cases (85%) and as non-homogenous in 9 (15%). Using the primary slides (conventional smear and TP) as a reference, additional diagnostic cells upgrading the cytologic diagnosis were found on the repeat slides in 7 cases (11.7%) and fungi consistent with Candida in 3 (5%). Conclusion: Repeat processing of residual cervical TP samples may not be an invariably reproducible procedure and the first slide may not be necessarily representative of the specimen as a whole. Nevertheless, both primary and repeat TP slides seem to be extremely effective in detecting a lesion (regardless of grade) in abnormal cases. The exact impact of non-homogeneous sampling of the vial on the diagnostic accuracy of the TP method should be further investigated.