Cervical Cytology (Pap, Liquid-Based)
Cervical cytology examines cells taken from the surface of the cervix and the endocervical canal to find pre-cancerous change and early cancer. Cells are collected with a spatula and brush, and either smeared on a slide (conventional method) or rinsed into a preservative fluid and processed into a thin layer (liquid based method).
The aim is to detect squamous and glandular precursor lesions, which are treated before cancer develops. Squamous lesions arise at the transformation zone, where the columnar epithelium of the canal meets the squamous epithelium of the ectocervix. Persistent infection with high risk human papillomavirus causes nearly all of them.
The test takes 5 minutes in clinic and is reported in 1 to 3 weeks. Liquid based preparation gives fewer unsatisfactory slides and leaves residual fluid for human papillomavirus testing, chlamydia and gonorrhoea tests. Its sensitivity for high grade lesions is similar to the conventional smear.
A single cytology test detects about 50 to 70% of high grade lesions (CIN 2 and worse), with a specificity over 95%. The sensitivity of the programme depends on regular repeat testing. Testing for high risk human papillomavirus is more sensitive (about 90 to 95%), and is used as the primary test in many programmes, with cytology used to triage positive results.
Most screening samples are normal. Abnormal results are found in about 5 to 10% of women screened, and most are low grade changes that regress.
Indications.
- Screening of women from the age set by the national programme (usually between 21 and 30 years) up to the age of about 64 to 69, at the programme interval.
- Follow up of a previous abnormal result, or after treatment of cervical precancer.
- Women with symptoms or an abnormal looking cervix, as an adjunct to colposcopy (cytology does not replace biopsy for a visible lesion).
- Women with HIV or other immunosuppression, screened more often.
- Vault samples after hysterectomy for cervical neoplasia.
Not indicated for diagnosing infections, or for women who have not had a pelvic or vaginal examination and are not sexually active, depending on the rules of the screening programme.
Contraindications and precautions.
- Menstrual bleeding: the sample is deferred, because blood hides cells.
- Acute cervical or vaginal infection: treat first when the discharge is heavy, since inflammation obscures cells.
- Recent intercourse, douching, vaginal creams, spermicides and lubricants in the preceding 48 hours.
- Pregnancy: screening is safe, with a spatula and a small soft brush. The brush is used with care when bleeding risk is present.
- Cervical stenosis, atrophy and post-radiotherapy changes make sampling difficult.
- Patients who decline or have pain, vaginismus or a history of abuse: explanation, a smaller speculum and consent at each step.
Preparation and technique.
The woman lies in the lithotomy or left lateral position. A speculum without lubricant (or with a small amount of water or lubricant that does not interfere) is inserted, and the cervix is brought into view. Cervical discharge is gently removed if heavy.
A spatula is placed against the ectocervix and rotated through 360° to sample the transformation zone. An endocervical brush is inserted into the canal and rotated through a half turn to a full turn, which samples the columnar cells.
In the conventional method, both are smeared thinly on a labelled slide and fixed at once in alcohol or spray. In the liquid based method, the head of the brush or spatula is rinsed vigorously in the vial of fluid, which is capped and labelled. The date of the last menstrual period, hormone use, age, previous results and the clinical findings go on the request.
