The cervical Pap smear is a long established screening test for cervical carcinoma. It identifies premalignant changes and allows selection of women with at-risk findings for more intense clinical examination, treatment and follow-up. It is very successful for detecting squamous lesions and can prevent most squamous cell carcinomas. In 1991, squamous cervical cancer occurred at a rate of 12.4/100 000. This had fallen to 5.4/100 000 by 2006.1 Some glandular abnormalities including adenocarcinoma in situ can also be identified on Pap smears, however this is not the main aim of cervical screening programs.
Australian guidelines 2,3 recommend screening every two years for all women over 18 years of age or two years after onset of sexual activity. Women over the age of 70 with two negative screens in the preceding five years can reasonably stop. The biggest risk factor for cervical cancer in Australia is not being screened, with 65% of all carcinomas identified in women who have been underscreened. The current Medicare Schedule provides a rebate for a conventional Pap smear.
Human papillomavirus is the main cause of cervical cancer. The transformation zone of the cervix is the area most susceptible to this infection and is sampled when collecting a Pap smear. This involves scraping the cervix transitional zone with a spatula or brush, then smearing the sample onto a glass slide and fixing with alcohol while still wet. Sampling should be taken by rotating the device around the endocervical canal. Abnormality develops at the squamo-columnar junction. This is the edge of any visible eversion/ectropion and care should be taken to sample this area.
Alternative monolayer technologies are equally effective but are not eligible for a Medicare rebate. After sampling, the plastic, not wooden, collection implement is vigorously agitated into a fixative solution to produce a cell suspension. This is subsequently processed in the laboratory to generate a more homogeneous specimen and a slide with cells spread one cell thick (thin layer or monolayer), with reduced obscuring factors such as blood or inflammation. After preparation of a conventional Pap smear, the plastic sampling brush can be rinsed into solution which can then be used for monolayer technology. Microbiological testing for chlamydia, by polymerase chain reaction, and DNA subtyping of human papillomavirus (HPV) can also be performed on this solution.
Currently, DNA human papillomavirus testing and subtyping for high-risk strains can be used as an indicator of risk of recurrence of high-grade abnormality and as a ‘test of cure’. A concurrent negative Pap smear with no high-risk human papillomavirus subtypes detected for two consecutive years enables a patient with a previous high-grade lesion to return from yearly screening to routine two-yearly screening. This use is covered by Medicare.