Pap smear: When to start and What to expect?

Pap smear/test is a screening test used to detect early changes in cervical cancer. "Pap" is named after Dr George Papanicolaou. Before the cells in the cervix turn into cancer cells, they undergo a few pre-cancerous changes. If these changes can be picked up early, then treatment can be given and cervical cancer can be prevented.

The precancerous cell changes are called dysplasia or cervical intraepithelial neoplasia (CIN). CIN can be divided into mild (CIN 1), moderate (CIN 2) and severe (CIN 3). CIN 1 usually can go away on its own but it still can progress to CIN 2/3. CIN 2 and 3 are more serious and need further test.

Through Pap smear, a brush is used to sample cells around the cervix and viewed under a microscope. Liquid-based cytology is more accurate compared to the conventional Pap smear. It is best to do pap smear between 10-20 days after the first day of menstruation.

Pap smear schedule:

Start: Age 21, or 3 years after first vaginal intercourse

Stop: Age 70, and with 3 consecutive negative tests, and no abnormal test in prior 10 years.

Post total hysterectomy: discontinue if benign reasons & no high grade CIN

Interval:

• Conventional pap test: annually
• Liquid-based cytology (LC): every 2 years
• LC with negative HPV test: every 3 years

•  For conventional and LC, if age >= 30 years old with 3 consecutive negative Pap smears, can repeat in 2-3 years.

 Updated Oct 2012

The American Congress of Obstetricians and Gynecologists has updated its 2009 practice bulletin on cervical cancer screening; its guidelines generally align with those released earlier this year (2012) by the U.S. Preventive Services Task Force, the American Cancer Society, and other groups.

Among the recommendations for routine screening:

• Women under age 21 should not be screened, regardless of behavioral risk factors. 
• For those aged 21 to 29, cytology alone should be performed every 3 years.
• For women aged 30 to 65, cytology plus human papillomavirus co-testing every 5 years is preferred; however, cytology alone every 3 years is acceptable.
• Women should not be screened after age 65 provided they've previously had sufficient negative screening results and no history of cervical intraepithelial neoplasia grade 2 or higher.
• More frequent screening may be required for women who have a history of cervical cancer or CIN2 or higher, who are immunocompromised (including HIV-infected), or who were exposed to diethylstilbestrol in utero.

    Pap smear

The Bethesda System is often used to interpret pap smear's result. In this system, the term squamous intraepithelial lesion (SIL) is used instead of CIN. 

Pap smear result can either be:

• Negative (normal)

• Atypical squamous cells of undetermined significance (ASC-US)
• most common result
• usually indicate HPV infection which may normalize if infection is cleared

• Squamous intraepithelial lesion - low grade (LSIL)
• equivalent to mild dysplasia (CIN 1)
• may goes away without treatment
• may indicate mild precancerous change

• Squamous intraepithelial lesion - high grade (HSIL)
• more likely to progress to cancer
• equivalent to CIN 2,3 and carcinoma in-situ

• Atypical squamous cells, cannot exclude HSIL (ASC-H)
• not clearly HSIL but could be

• Atypical glandular cells  (AGC)
• suggest precancer cells

• Cancer
• abnormal cells may have spread deeper

Abnormal Pap smear results will require further tests, either repeat Pap smear, do HPV test or colposcopy. Biopsy or other minor intervention such as conization, cryocauterization, laser therapy, large-loop excision of the transformation zone or endometiral sampling may be needed.

      Follow up test for abnormal pap smear result