A retrospective analysis of 94 patients with CIN and false negative cervical smears taken at colposcopy.

This report investigates the reasons for false negative cervical cytology in 94 out of 630 patients (15%) in whom cervical intraepithelial neoplasia (CIN) was diagnosed on colposcopically directed biopsy. Cervical smears were taken immediately before biopsy and the cases with false negative cytology were compared with those whose cytology was abnormal. Patients with false negative cytology were more likely to have been younger (P < 0.01), to have had fewer pregnancies (P < 0.001), to have had a less severe grade of dyskaryosis on their referral smear (P < 0.001), to have had no endocervical cells on the smear (P < 0.05), to have had a less severe grade of CIN on biopsy (P < 0.001), to have had no punctation visible at colposcopy (P < 0.01), and to have had no mosaic pattern seen at colposcopy (P < 0.05). We found no effect attributable to the patient's menstrual history, the interval between referral smear and colposcopy clinic visit, the smear taker or the type of spatula used to take the smear.