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  Imaging systems, workload limits, and screening accuracy


CAP Today




January 2011

Roger B. Lane, MD

The ThinPrep imaging system is an FDA-approved device that scans and locates 22 fields of view (FOV) for gynecologic ThinPrep slides based on nuclear:cytoplasmic ratio, nuclear size, and nuclear staining characteristics. After evaluating each FOV, a cytotechnologist may sign out a case as negative if no abnormalities are found. If abnormalities are found, manual review of the entire glass slide is required. FDA approval of the ThinPrep imaging system included the acceptance of a higher screening limit of 200 slides per day, compared with 100 slides per day for manual ThinPrep screening. (The FDA recently clarified that the 200-slide limit applies only to slides that do not undergo manual review of the entire slide.) A recent study by Tarik M. Elsheikh, MD, et al, investigates the effect of increasing workload on the performance of cytotechnologists using the ThinPrep imaging system (Cancer Cytopathol. 2010;118:75–82).

In this study, workloads for three cytotechnologists using the ThinPrep imaging system were increased over an eight-week period from an average of 87 slides per day to 118 slides per day. The first phase lasted three weeks, during which time the cytotechnologists were asked to screen at their usual speed, to establish a baseline performance. In phase two (three weeks duration), they were asked to screen as fast as they could without feeling they were compromising the quality of their work. In phase three (two weeks duration), they were asked to meet a certain productivity expectation (15 percent higher than their average productivity in phase two). The cytotechnologists were blinded to the purpose of the study, and non-participating cytotechnologists re-screened all slides.

An increased workload correlated with a decreased percentage of cases undergoing manual review, lower detection of abnormal findings, and an increased false-negative fraction rate. El-sheikh, et al, concluded that increasing cytotechnologist workloads to greater than 100 slides per day with the ThinPrep imaging system results in a significantly reduced screening performance.

The article includes a description of the clinical trial study that led to FDA approval of the ThinPrep imaging system, including a discussion of the limitations of the data that led to approval of a 200-slide per day maximum screening rate. In addition, there is an interesting discussion of post-study interviews with participating cytotechnologists about their experience and their reactions to the study.

A second recommended reading, also by Elsheikh, et al, is a study that measured the screening accuracy of four cytotechnologists during different days of the week and at different times during the day using the ThinPrep imaging system (Cancer Cytopathol. 2010;118:41–46). The study was conducted over an eight-month period, and multiple measures of accuracy were followed, including individual workload, detection rate of atypical squamous cells (ASC) and low-grade squamous intraepithelial lesions (LSIL), total abnormal rate, high-risk human papillomavirus positivity rates associated with ASC, false-negative fraction, and workload.

The authors found that three of the four cytotechnologists detected significantly fewer abnormal cases on one day of the week (one on Mon-day, two on Friday). Two cytotechnol-ogists detected significantly fewer total abnormal cases in the afternoon than in the morning; this was strongly coordinated with increased speed in the afternoon and decreased detection of ASC cases. The study provides evidence that individual cytotechnologists may have particular trends that are worth noting and monitoring. There is discussion of how these types of monitors can be used to detect differences in sensitivity relating to workload and how they can be used to determine the cause and suggest options to correct any decrease in sensitivity.

Finally, a third recommended reading is a review by Andrew A. Renshaw, MD, and Dr. Elsheikh, which proposes ways to improve quality assurance in cytopathology (Diagn Cytopathol. 2010;38:772–775). The article begins with a review of limitations of the CLIA ’88 mandates con-cerning assessment of cytotechnologist workload and screening accuracy. The authors discuss why they believe the CLIA mandates are insufficient to determine the quality of Pap test interpretation in actual clinical practice.

The article provides an interesting discussion of how “controls” are uncommonly used in cytopathology but could be useful to improve the practice of gynecologic cytology. Among the possible uses of controls are inserting known abnormals into routine material as a method to measure the sensitivity of screening, or, alternatively, prescreening slides and using the abnormal cases in the material itself as a control. In addition, the authors suggest that monitoring screen-ing sensitivity during the morning versus afternoon and on different days of the week can be used as a control to determine workload limits for cytotechnologists based on any trends in decreased sensitivity during certain times of the day or week for individual cytotechnologists.

The studies by Elsheikh, et al, and the review by Renshaw and Elsheikh are recommended reading for all involved in gynecologic cytology. They provide informative discussions of current issues regarding effective monitoring of screening accuracy and provide helpful ideas for defining appropriate workload limits for individual cytotechnologists.

Dr. Lane, a member of the CAP Cytopathology Committee, is a pathologist with Southeastern Pathology Associates, Brunswick, Ga.