Anal Pap Smear Procedure
Specimen Collection Technique
The anal Pap test involves blind insertion of a Dacron or polyester swab approximately 4-6 cm into the anal canal, rotating it 360 degrees while withdrawing to sample the transformation zone, then either fixing cells on a slide (conventional method) or placing the swab in liquid-based cytology medium. 1
Step-by-Step Collection Method
- Insert the moistened swab (with water or saline) 4-6 cm into the anal canal past the anal verge 2
- Rotate the swab 360 degrees while applying gentle lateral pressure against the anal canal wall 2
- Slowly withdraw the swab while continuing rotation to maximize cellular collection 1
- For conventional cytology: immediately smear the swab onto a glass slide and fix with cytology fixative 1
- For liquid-based cytology: place the swab directly into the collection vial and agitate to release cells 1
Self-Collection vs. Physician-Collection
Self-collected anal Pap specimens are equally adequate for cytologic interpretation compared to physician-collected specimens, with 78% adequacy rates and high patient satisfaction. 3
- Self-collection is preferred by 75% of patients when offered the option 3
- No statistically significant difference exists in specimen adequacy between self-collected and physician-collected samples 3
- Self-collection may improve screening compliance and is more feasible in primary care settings 3
Cytologic Interpretation
The anal Pap is interpreted using the standardized Bethesda System classification, identical to cervical cytology 1:
- Normal - no abnormal cells identified
- ASCUS (Atypical Squamous Cells of Undetermined Significance) - equivocal findings
- LSIL (Low-Grade Squamous Intraepithelial Lesion) - mild dysplasia
- HSIL (High-Grade Squamous Intraepithelial Lesion) - moderate to severe dysplasia
Follow-Up for Abnormal Results
Abnormal anal Pap smear findings (ASCUS or worse) should be further evaluated by high-resolution anoscopy with biopsy of abnormal areas and topical therapy of high-grade dysplastic lesions. 4
- High-resolution anoscopy (not routine anoscopy) is the diagnostic standard for evaluating abnormal cytology 1
- The technique is analogous to cervical colposcopy, using magnification and acetic acid application to identify dysplastic areas 1
- Directed biopsies are performed on acetowhite lesions for histologic confirmation 1
High-Risk Populations Requiring Screening
The following groups have substantially elevated anal cancer risk and warrant screening 2:
- HIV-positive men who have sex with men - highest risk at 70 per 100,000 (35-70 times general population risk) 1
- HIV-positive women - increased risk due to immunosuppression 1
- Men who have sex with men regardless of HIV status 2
- Women with history of cervical, vulvar, or vaginal cancer or high-grade cervical lesions 2
- Immunocompromised patients (transplant recipients, chronic immunosuppression) 1
- Women participating in receptive anal intercourse 2
Important Limitations and Caveats
The anal Pap test has highly variable sensitivity (26-69%) and specificity (59-92%) depending on the population and cytologic threshold used, with performance characteristics similar to cervical Pap testing. 1
- Sensitivity is lower in HIV-negative males (26-47%) compared to HIV-positive males (46-69%) 1
- Test performance depends heavily on pathologist experience - reported results generally represent best-case scenarios from specialty clinics 1
- HPV DNA testing is not useful as an adjunct to anal Pap screening because HPV prevalence is extremely high (>90%) in high-risk populations, precluding discriminatory value 1
Current Screening Recommendations
- No universally accepted guidelines or formal screening programs exist for anal dysplasia provincially, nationally, or internationally 1
- The New York State Department of Health AIDS Institute recommends annual anal Pap testing in high-risk groups 1
- Most jurisdictions do not reimburse for anal Pap testing in men or women 1
- No direct evidence exists that anal Pap screening programs reduce anal cancer mortality or morbidity, though strong parallels exist with cervical cancer screening 1