What Does a Pap Smear Test Tell You
A Pap smear is primarily designed to detect abnormal cervical cells that may indicate precancerous or cancerous changes in the cervix, allowing for early detection and treatment of cervical cancer before it develops or progresses. 1
Purpose and Function of Pap Smears
A Pap smear (Papanicolaou test) serves as a screening tool that:
- Detects abnormal cervical cells that may indicate precancerous conditions
- Identifies cellular changes caused by human papillomavirus (HPV) infection
- Screens for cervical intraepithelial neoplasia (CIN) and cervical cancer
- Helps classify abnormalities according to standardized terminology
What Pap Smear Results Can Show
Pap smear results are typically reported using the Bethesda System terminology 2, which includes:
- Normal findings: Negative for intraepithelial lesion or malignancy (NILM)
- Abnormal findings:
- Atypical squamous cells of undetermined significance (ASC-US)
- Atypical squamous cells cannot exclude high-grade lesion (ASC-H)
- Low-grade squamous intraepithelial lesions (LSIL)
- High-grade squamous intraepithelial lesions (HSIL)
- Atypical glandular cells (AGC)
What Pap Smears Can Detect
HPV-related changes: The Pap test can identify cellular changes consistent with HPV infection, which is present in approximately 80-85% of LSIL cases 2
Precancerous lesions: Detects cervical intraepithelial neoplasia (CIN) grades 1,2, and 3, with CIN 3 representing the most severe precancerous condition
Cervical cancer: Can detect both squamous cell carcinoma (approximately 78% of cases) and adenocarcinoma (approximately 22% of cases) 2
Occasionally, endometrial abnormalities: While not designed for this purpose, Pap tests sometimes detect abnormal endometrial cells that may warrant further investigation 3
Limitations of Pap Smears
It's important to understand what Pap smears cannot reliably detect:
- Not for STD screening: Pap tests are not designed to screen for sexually transmitted infections other than HPV 2
- Limited sensitivity: A single Pap test has variable sensitivity (32-92%) for detecting cervical abnormalities 2, which is why regular screening is important
- Not for HPV typing: Standard Pap tests don't identify specific HPV types; separate HPV DNA testing is needed for that purpose
- Not for endometrial cancer screening: While sometimes detecting endometrial abnormalities, Pap tests are not reliable for endometrial cancer screening 2
Clinical Significance and Follow-up
The management of abnormal Pap results depends on the specific finding:
- ASC-US: May warrant HPV testing (for women ≥21 years) to determine if colposcopy is needed 2
- LSIL: Generally requires colposcopy with directed biopsy 2
- HSIL: Requires colposcopy or expedited treatment due to high risk of significant disease 2
- AGC: Requires colposcopy and possibly endocervical sampling 2
Important Considerations
- Pap smear screening has reduced cervical cancer mortality by over 70% in the United States 1
- The average progression time from high-grade precancerous lesion to invasive cancer is approximately 10 years, allowing ample opportunity for detection 1
- Women often confuse having a pelvic examination with having a Pap test; healthcare providers should clarify when a Pap test is being performed 2
- HPV vaccination status does not change screening recommendations 1
Pap smears remain a cornerstone of preventive healthcare for women, providing a valuable tool for early detection of cervical abnormalities that could progress to cancer if left untreated.