Identification of Trichomonas vaginalis in different Papanicolaou test preparations: trends over time in the College of American Pathologists educational Interlaboratory Comparison Program.

Context: The College of American Pathologists' Interlaboratory Comparison Program in Gynecologic Cytology has seen an increase in enrollment in liquid-based Papanicolaou test challenges with a decrease for conventional Papanicolaou tests. Trichomonas vaginalis can be difficult to identify in all preparation types.

Objectives: To evaluate 20 years of participant results from the College of American Pathologists Interlaboratory Comparison Program in Gynecologic Cytology for Trichomonas to ascertain whether performance has changed because of the introduction of liquid-based Papanicolaou and proficiency testing.

Design: Concordance rates for the target diagnosis of Trichomonas vaginalis were evaluated for 167,956 participant responses (1990-2010). A nonlinear mixed model was fit with participant type, preparation type, and a 2-level program year (1990-2005 and 2006-2010) reflecting before and after proficiency testing began. A repeated-measures component allowed modeling of the slide-specific performance to ensure that the overall results were not based on the performance of a few slides.

Results: Cytotechnologists had higher concordance with the target diagnosis than did pathologists (89.8% [72,992 of 81,319] versus 83.4% [72,271 of 86,637], P < .001) and better performance for each preparation type (P = .003). Concordance initially dropped after the introduction of proficiency testing (P < .001) for conventional and liquid-based (SurePath) preparations by both participant types, followed by quick, parallel improvement.

Conclusions: Performance is high in the detection of Trichomonas vaginalis in the College of American Pathologists Interlaboratory Comparison Program in Gynecologic Cytology. Liquid-based Papanicolaou and proficiency testing minimally affected participant performance. Cytotechnologists performed better over time and across preparation types than did pathologists, although pathologists showed performance results parallel to that of the cytotechnologists. Awareness of the performance differences by pathologists and cytotechnologists, as well as their difference in proficiency among liquid-based techniques, may help ensure accurate results in clinical practice.