Information for general practitioners about anal Pap tests
What is an anal Pap test?
The anal Pap test is a method for screening for anal cancer and precancerous lesions. It essentially uses the same techniques as those of cervical screening.
Note that this technique is still being evaluated, and that there is currently no Medicare rebate.
How can I take an anal Pap test?
It is very important that you appropriately counsel your patients regarding the potential risks and benefits of the procedure before undertaking an anal Pap smear.
Cytological examination of anal specimens is quite specialised, and you should first discuss this with your local laboratory before sending any material.
It is currently unknown whether anal douching prior to taking the test affects the quality of the specimen.
Cells from the lining of the anal canal are collected using a Dacron swab, pre-moistened with tap water. It is inserted 5cm, directly into the anal canal, without the use of a proctoscope. In a spiral manner, and with firm pressure, it is rotated and gradually withdrawn over a 1 minute period.
The swab is then eluted into a fixative (such as ThinPrepTM) and sent to a laboratory.
If anal cancer is a significant concern, then a digital ano rectal examination should be performed after the Pap smear has been taken.
Consider screening for other anal STIs, if the history suggests that the person may be at risk.
What are the potential problems?
The procedure itself is usually well tolerated, although some people have some mild discomfort during and immediately after the swab has been taken. Rarely, minor bleeding is noted for a short while afterwards.
What will the anal Pap test result be?
The result will be one of:
- Technically inadequate – this is usually because there are not enough cells in the specimen for the cytologist to confidently make a diagnosis
- Normal – no abnormal cells identified
- Low-grade squamous intraepithelial lesion (LSIL) - sometimes called AIN1. Thought to be a result of infection with low risk HPV types, and to be of low risk for progression to anal cancer.
- Atypical squamous cells of undetermined significance (ASCUS) – cells present that lead the cytologist to have a concern that significant dysplasia may be present, but features not sufficiently clear to make a definitive diagnosis.
- High-grade squamous intraepithelial lesion (HSIL) - sometimes called AIN2 or AIN3. Severely dysplastic cells present. Thought to be a result of infection with high risk HPV types, and to be of significant risk for progression to anal cancer.
It is very important that you appropriately counsel your patients regarding the possible meaning of the results.
Caution is required in the interpreting of anal Pap results. The sensitivity and specificity are typically around 60%. It is important to note that this test does not reliably detect cancer - if you have any concerns, then please refer urgently for a specialist opinion.
If you suspect that your patient is at very high risk of anal cancer, they may be referred to the Dysplasia and Anal Cancer Services (DACS), IBAC, Level 4 Xavier Building, at St. Vincent's Hospital, Sydney. Your patient will need a referral letter. However, if the matter is urgent, please ring (02) 8382 3707.