Unsatisfactory slides added to 2004 gyn graded slide sets
Michael A. Schulte, MD
Beginning this year, unsatisfactory slides will be included in graded slide sets for the CAP’s Interlaboratory Comparison Program in Gynecologic Cytopathology, or Pap program. Unsatisfactory slides previously were available only in educational sets.
The 2002 Pap program year-end summary shows that 88.6 percent of participants’ diagnoses agreed with the reference diagnosis of unsatisfactory for conventional Pap slides. For ThinPrep slides, 95 percent of participants arrived at the correct diagnosis (unsatisfactory). All unsatisfactory slides included in the 2004 graded slide sets have been validated, and the 2004 program response forms will be modified to reflect inclusion of "unsatisfactory" as an interpretive choice.
One factor preventing inclusion of unsatisfactory slides in the graded program until now has been ambiguous criteria for determining adequacy for gynecologic cytology. Bethesda 2001 has created new adequacy criteria that allow more reproducible interpretations. According to Bethesda criteria, an adequate conventional smear should have an estimated minimum of 8,000 to 12,000 well-preserved and well-visualized squamous epithelial cells. Endocervical cells and cells that are completely obscured should not be included in the estimated range, and individual cells should not be counted on conventional slides.
The revised Bethesda atlas will include reference images of slides of known cellularity for comparison with slides being examined (see "Revised Bethesda atlas fine-tuned and first-rate," page 36). For liquid-based preparation slides, a minimum of 5,000 well-visualized and well-preserved squamous cells should be present for an adequate preparation. A cell count is necessary with such slides to determine adequacy. Ten 40¥ fields are counted across the diameter of the material. The average number of cells needed for an adequate preparation depends on the diameter of the material on the slide, magnification of the objective lens, and field number of the eyepiece. For example, with a 20-mm-diameter preparation using a 40¥ objective lens and an eyepiece with a field number of 22, an average of 3.8 cells per field (with 10 fields counted) is needed for adequate preparation.
Bethesda 2001 adequacy criteria have been published in the Journal of the American Medical Association (Solomon D, et al. 2002; 287: 2114- 2119); however, a more detailed explanation and a summary table for determining the minimum number of cells will be included in the 2004 Bethesda atlas, slated to be published by Springer-Verlag in February or March.
Dr. Schulte, a member of the CAP Cytopathology Committee, is cytopathology section director of Covenant Laboratories and Midwest Clinical Laboratories and laboratory director, St. Michael Hospital, Milwaukee.