Partial rescreening of all negative smears: an improved method of quality assurance in laboratories undertaking cervical screening.

Partial rescreening was carried out on 9633 cervical smears reported as negative by standard screening. Each slide was 'step-screened' at normal speed for 30 s. Thirteen false negative smears were detected by this method. No false negatives were revealed by conventionally rescreening 10% of the same study group. The sensitivity of the method was assessed by 'step-screening' 100 known positive smears. Of this group 92 were detected. The results indicate that partial rescreening is a sensitive method of quality assurance and should replace conventional 10% proportional rescreening, which is ineffective.