Cervical Screening Programme
Department of Health
The Government of the Hong Kong Special Administrative Region

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The sensitivity of the cervical smear depends greatly on the quality of the smear. Appropriate timing: avoid cervical screening during menstruation because blood stained smear may be difficult to interpret and may give rise to false negative smear results. Correct site of sampling (transformation zone). Adequate cervical cells obtained (both ectocervical and endocervical components) using appropriate sampler: the presence of endocervical cells on the sample has been recommended as a marker of adequacy of cervical cell collection as they imply the upper limit of transformation zone was included in the specimen. Proper fixation and proper storage of specimen. Correct labeling of specimen and cytology request form filled with adequate clinical details. Timely delivery to laboratory. Common reasons for screening failure leading to false negative results: Causes of false negative results Source of error Solution Sampling failure - Failure in sampling the abnormal area - Failure in obtaining adequate cellular component for diagnosis - Excessive blood, traumatized cells, mucus or inflammation - The lesion fails to exfoliate despite adequate sampling. - Ensure adequate exposure of cervix - Target the sampler towards the transformation zone - Circumferential collection of adequate samples Transfer failure - Failure in transferring the abnormal cells onto the slide. Only about 20% of cells collected can be transferred to the slide. - Unsatisfactory preparation of the slide such as blood smear with traumatized cells, layering of cells, air-drying of slide and fixation artefact - Liquid-based cytology may provide better cells sample - Fixate soon after taking the smear Laboratory failure - Smear of poor quality - Cells distorted by air-drying - Scanty material for interpretation - Liquid-based cytology may provide better cells sample - Properly trained staff for slide interpretation - Computer assisted slide interpretation Timing of Cervical Smear Taking Communication with Clients Equipment for Smear Taking Right Environment & Correct Positioning Insertion of Speculum Cervical Cells Sampling Management of Cells Collected

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