Pap smear

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Pap Smear (Papanicolaou Test)

Overview

The Pap smear, named after its developer George Papanicolaou who introduced it in the 1920s, is a cervical cancer screening test that uses exfoliated cells scraped from the cervix to detect dysplastic or malignant changes under microscopy. It has been one of the most successful cancer screening tools in history - observational studies show a 60-90% reduction in cervical cancer incidence and 20-60% reduction in mortality in populations with widespread screening programs. - Junqueira's Basic Histology, p. 1151; Symptom to Diagnosis, p. 34

Anatomy and the Transformation Zone

The area of greatest clinical importance is the transformation zone (TZ) - where the squamous epithelium of the ectocervix meets the mucus-secreting columnar epithelium of the endocervix at the squamocolumnar junction (SCJ). This zone must be completely sampled for an adequate Pap smear. The SCJ location changes with age:

Cervical transformation zone anatomy by age group - showing SCJ location at puberty, reproductive age, and menopause

At puberty: SCJ is large and visible on the ectocervix
Reproductive age: SCJ migrates, TZ is identifiable but the original SCJ is no longer visible
Menopause and older: SCJ migrates into the canal and is no longer visible - this can limit sampling

Epithelial dysplasia begins in metaplastic cells of the TZ, typically occurring at a mean age of 54 for squamous cell neoplasia. HPV infection is strongly implicated. - Pfenninger and Fowler's Procedures for Primary Care, p. 1053

Technique

Equipment

Speculum and exam gloves
Sampling devices: Cytobrush, Cervex-Brush (broom), or Papette - the cotton swab and tongue blade are discouraged
Glass slides + fixative spray, or liquid-based transport medium (ThinPrep, SurePath)

Step-by-Step Procedure

Insert speculum, visualize the cervix - note the TZ, SCJ, and any gross lesions
Gently blot (do not rub) excess mucus only if truly necessary - it may contain exfoliated cells needed for analysis
Endocervical sampling: Insert the Cytobrush into the canal, rotate 90-180 degrees only (more rotation causes bleeding that can wash away or obscure abnormal cells)
Ectocervical/TZ sampling: Rotate a spatula 360 degrees over the entire TZ; or use broom devices (Cervex-Brush, Papette) which sample both areas simultaneously with 5 rotations of 360 degrees
Glass slide method: Apply ectocervical spatula sample first, then roll the Cytobrush material over it, spray with cytofixative within 5 seconds to prevent drying artifact
Liquid-based method: Rinse the device into a vial of transport liquid (ThinPrep or SurePath) instead of applying to glass slides
Obtain cervical cultures after cytologic sampling if indicated

Pfenninger and Fowler's Procedures for Primary Care, pp. 1054-1058

Methods: Conventional vs. Liquid-Based Cytology

Feature	Conventional	Liquid-Based (ThinPrep/SurePath)
Cell application	Spread directly on glass slide by examiner	Cells rinsed into vial, processed in lab
FDA approval	Standard	Both approved as alternatives
HPV reflex testing	Not available	ThinPrep only (FDA-approved for reflex HPV)
Sensitivity/specificity	Similar	Similar (no advantage in detection of high-grade CIN)
Advantage	Lower cost	Allows "reflex" HPV testing on same specimen; fewer inadequate samples

Liquid-based Pap smear testing is neither more sensitive nor more specific for high-grade CIN compared to the conventional Pap. The clearer advantage is the ability to perform reflex HPV DNA testing from the same vial. - Pfenninger and Fowler's Procedures for Primary Care, p. 1054

Test Characteristics

Sensitivity for HSIL: ~56%; for LSIL: ~77%
Specificity for HSIL: ~97%; for LSIL: ~80%
HPV testing is more sensitive but less specific for CIN 2/3; false-positive rates are higher in women under 35
Symptom to Diagnosis, p. 34

Bethesda 2001 Classification System

Pap smear results are reported using the Bethesda 2001 terminology:

1. Negative for Intraepithelial Lesion or Malignancy (NILM)

Normal, including benign cellular changes

2. Epithelial Cell Abnormalities - Squamous

Bethesda Term	Histologic Equivalent	Meaning
ASC-US	Variable	Atypical squamous cells of undetermined significance
ASC-H	Variable	Atypical squamous cells, cannot exclude HSIL
LSIL	CIN 1 (mild dysplasia), HPV effect	Low-grade squamous intraepithelial lesion; ≤1/3 of epithelium involved
HSIL	CIN 2/3, CIS	High-grade squamous intraepithelial lesion; >1/3 to entire epithelium involved
Squamous cell carcinoma	Frankly invasive cancer	Invasion >3 mm below basement membrane

3. Epithelial Cell Abnormalities - Glandular

AGC (atypical glandular cells) - previously called AGC-US, but the "US" was dropped because 10% harbor cancer and 25% harbor high-grade lesions; all AGC reports require further investigation
Atypical endocervical/endometrial cells, favor neoplasia
Endocervical adenocarcinoma in situ (AIS)
Adenocarcinoma

Histologic and cytologic correlations of cervical dysplasia - CIN I through invasive cancer with Bethesda terminology

The diagram above shows the correlation between the degree of epithelial involvement and cytologic findings. Invasion below the basement membrane signals invasive cancer.

Pfenninger and Fowler's Procedures for Primary Care, Box 151-2; Swanson's Family Medicine Review

Screening Guidelines

USPSTF 2018 (Grade A)

Age Group	Recommendation
< 21 years	No screening (Grade D)
21-29 years	Cytology (Pap smear) every 3 years
30-65 years	Cytology every 3 years, OR HPV alone every 5 years, OR co-testing (cytology + HPV) every 5 years
> 65 years	Discontinue if adequate prior screening (3 consecutive negative cytology or 2 negative HPV results within last 10 years, most recent within 5 years)
Post-hysterectomy (benign, no CIN 2/3 history)	Discontinue (Grade D)

ACOG 2016

Cytology every 3 years for women ages 21-65, or
Cytology every 3 years (ages 21-29) + co-testing (cytology + HPV) every 3 years for ages 30-65

Special Situations

Post-dysplasia treatment: Continue Pap smears at least annually for life (significant recurrence risk)
After hysterectomy for dysplasia/cancer: Continue annually after 3-4 normal smears at 4-6 month intervals
DES-exposed offspring: Require modified protocols and colposcopic evaluation
Immunocompromised women: Continue screening beyond age 65
Rape/abuse victims: Pap smear is part of the initial work-up
Symptom to Diagnosis, p. 34; Pfenninger and Fowler's Procedures for Primary Care, pp. 1052-1053

Management of Abnormal Results

Result	Management
ASC-US	(1) Repeat cytology at 6-month intervals x2; or (2) Reflex HPV DNA testing - colposcopy if high-risk HPV+; or (3) Immediate colposcopy. HPV-based triage has 90-96% sensitivity vs. 75-85% for repeat Pap. HPV-negative ASC-US has ≥98% negative predictive value.
ASC-H	Colposcopy
LSIL	Colposcopy (majority resolve spontaneously - ablative/excisional therapy NOT acceptable without first doing colposcopy)
HSIL	Colposcopy with endocervical curettage
AGC	Colposcopy + endocervical sampling; if no lesion found, endometrial sampling
Any gross cervical lesion	Pap smear is NOT diagnostic - biopsy directed by colposcope is required regardless of Pap result

Swanson's Family Medicine Review, pp. 1757-1779

Risk Factors for Cervical Neoplasia

HPV infection (necessary precursor; HPV 16 carries the greatest risk)
Most HPV infections (90%) resolve within 2 years; the persistent 10% have potential to progress
Smoking
Immunocompromised state
Early age of first intercourse
Multiple sexual partners
Alcohol use is not an associated risk factor

Relative Contraindications

There are no absolute contraindications to obtaining a Pap smear. Relative contraindications include active vaginitis, cervicitis, PID, or menses - where sample collection or interpretation may be difficult. However, the Pap smear should still be obtained if clinically warranted.

Pfenninger and Fowler's Procedures for Primary Care

Recent Evidence (2024-2026)

A 2026 systematic review and meta-analysis (PMID 42142346) examined liquid-based cytology vs. conventional Pap smear in cervical cancer screening - supporting the continued role of both methods. A 2024 systematic review (PMID 39558397) assessed AI in cytopathology, noting promising accuracy for automated Pap smear reading - though this is not yet standard of care.

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