Quality control in cervicovaginal cytology by cytohistological correlation

Frequent studies attest to the correlation of cytological interpretations with defined histopathological entities. Nevertheless, as part of quality control, cytology laboratories are required to compare Papanicolaou smear reports with those of cervical biopsies to search for discrepancies. We have attempted to determine and categorize the causes of existing discrepancies in our laboratory in order to clarify the source of errors.

We reviewed 670 cervical smears that were paired with subsequent punch biopsy or endocervical curettage samples, obtained within 2 months of the cytology, and found out that 60 smear-biopsy pairs were discrepant regarding the diagnosis. These cases were categorized into four error groups after careful re-evaluation of the original smear and biopsy slides.

In 51 (85%) of 60 cervical smear-biopsy pairs with reports that disagreed, the initial diagnoses of both cervical smear and biopsy were confirmed by the review opinion; in these cases, cytology and biopsy 'sampling errors' were responsible for 40 and 11 instances of discrepancy, respectively. Seven cases (11.1%) were discrepant due to 'smear interpretation errors' and consisted of five cases with initial under-diagnosis and two cases with initial over-diagnosis. One case (1.7%) was due to 'screener error'. In another case, discordance was due to cervical 'biopsy interpretation error', with initial over-diagnosis as squamous intraepithelial lesion.

In this retrospective study, we determined the causes of cytohistological discrepancies in cervical samples. The main explanation for discrepancy was 'sampling error'.