The "Inconclusive--possible high grade epithelial abnormality" category in Papanicolaou smear reporting.

Background: The Australian Terminology for Cervical Cytology Reporting includes the category "Inconclusive-Possible high grade epithelial abnormality."
Methods: The frequency of use of this category, the types of associated cell patterns, and the yield of high grade lesions at biopsy were studied.
Results: One hundred and two cases categorized as "Inconclusive" were reported between January and June 1995, representing 0.24% of 41,712 Papanicolaou (Pap) smears screened. The abnormal cells were reported as squamous in 74.5% of cases, endocervical in 4.9% of cases, endometrial in 3.9% of cases, and indeterminate in 16.7% of cases. The main cellular patterns included disorganized groups of hyperchromatic squamous, glandular, or indeterminate cells (64.2% of cases) and atypical metaplastic squamous cells (28.4% of cases). Cell preservation was suboptimal. In 25.3% of cases the cells were highly degenerate or air-dried. Follow-up included biopsy (84.3% of cases), colposcopy alone (7.8% of cases), and repeat Pap smears without any detected abnormality (3.9% of cases). No follow-up was available in 3.9% of cases. High grade abnormalities were found in 66.3% of the biopsied cases and 55.9% of the total cases (48 cervical intraepithelial neoplasia [CIN] of Grade 2 or 3; 2 squamous cell carcinomas; 3 endocervical adenocarcinoma in situ [ACIS]; 3 adenocarcinomas of endocervical, ovarian, and endometrial origin; and 1 endometrial stromal sarcoma). In 16.2% of cases a low grade squamous lesion was present on biopsy (CIN, Grade 1 or human papillomavirus effect); and no lesion was found in 17.4% of cases.
Conclusions: The "Inconclusive" category was not overused, and gave a high yield of biopsy abnormalities. Accepting uncertainty in the diagnosis of some high grade lesions reduces their likelihood of being classified incorrectly as reactive changes, ignored because of poor cell preservation, or lost in the larger group of classifications such as atypical cells of undetermined significance, borderline nuclear abnormality, or non-specific minor changes.