Pap Smear: What It Is, How It Works, and Results

What Is a Pap Smear?

A Pap smear — also called a Pap test or cervical cytology — is a screening procedure that collects cells from the cervix and examines them under a microscope for abnormalities that may indicate pre-cancerous change or cervical cancer. It is one of the most successful cancer screening tests in medical history. Since the widespread adoption of Pap smear programs in the 1950s and 1960s, cervical cancer mortality in the United States has declined by approximately 70% — a reduction almost entirely attributable to the detection and treatment of pre-invasive cervical lesions through routine Pap screening.

The test was developed by Dr. Georgios Papanicolaou, a Greek-American physician who observed characteristic cellular changes in cervical cancer cells in the 1920s and spent two decades developing, validating, and advocating for cytological cervical screening before his methods gained widespread clinical acceptance. His landmark 1943 monograph, “Diagnosis of Uterine Cancer by the Vaginal Smear,” established the scientific basis for cervical cytology screening.

For context on how the Pap smear fits into the broader cervical cancer screening landscape, see our guide to cervical cancer screening. For information about cervical cancer itself, see our guide to cervical cancer.

What Does a Pap Smear Test For?

A Pap smear tests for cervical intraepithelial neoplasia (CIN) — pre-cancerous changes in cervical cells — and early-stage cervical cancer. Understanding what a Pap smear does and does not test for helps women interpret their results correctly and understand why other gynecological screening tests may also be recommended:

What a Pap smear DOES test for:

• Abnormal cervical cells (squamous cell and glandular cell abnormalities)
• CIN grades 1, 2, and 3 (mild, moderate, and severe pre-cancerous changes)
• Early squamous cell carcinoma and adenocarcinoma of the cervix

How a Pap Smear Is Performed

A Pap smear is typically performed in a healthcare provider’s office during a routine pelvic examination. The procedure takes approximately 5–10 minutes and is performed with the patient lying on an examination table with feet in stirrups (lithotomy position):

1. Speculum insertion: A lubricated speculum is gently inserted into the vagina and opened to expose the cervix. The speculum may feel like mild pressure; taking a slow deep breath during insertion can help with relaxation.
2. Ectocervical sampling: A plastic spatula is used to gently sweep cells from the outer surface of the cervix (ectocervix), which is the primary site for squamous cell pre-cancerous changes.
3. Endocervical sampling: A small endocervical brush is inserted approximately 1cm into the cervical os to collect cells from the endocervical canal and transformation zone — the junction where glandular cells meet squamous cells and where most cervical cancers originate.
4. Sample processing: Both the spatula and brush are rinsed into a small vial of liquid preservative medium (liquid-based cytology, or LBC). This replaces the older method of smearing cells directly onto a glass slide. The same liquid-based vial can be used for both cytological analysis and HPV DNA testing, enabling co-testing without a second specimen collection.
5. Laboratory analysis: The vial is sent to a cytology laboratory, where cells are processed, examined by a cytopathologist, and reported using standardized Bethesda System terminology.

Most women experience only mild pressure or brief cramping during the endocervical brush insertion. Some light spotting after the procedure is normal and resolves within 1–2 days. Women with severe discomfort, a history of vaginismus, or postmenopausal vaginal atrophy should inform their provider beforehand — smaller specula, additional lubricant, and slower technique can significantly improve comfort.

How to Prepare for a Pap Smear

Certain conditions and activities can reduce the accuracy of a Pap smear by obscuring or removing cells from the sampling area. To maximize test accuracy:

Timing:

• Schedule the Pap smear at a time when you are not menstruating, if possible; moderate to heavy menstrual blood can interfere with cell analysis
• Light spotting is generally acceptable; the provider will advise whether to reschedule
• Mid-cycle (days 10–20 of a typical 28-day cycle) is generally ideal

48 hours before the appointment, avoid:

• Sexual intercourse (semen, lubricants, and introduced cells can alter the specimen)
• Vaginal douching (removes natural flora and superficial cervical cells)
• Vaginal medications, creams, or suppositories (including antifungal preparations, hormonal creams, or spermicides)
• Tampon use (removes exfoliated cells from the vaginal canal)

Routine bathing and showering are appropriate. These restrictions exist because the cervical cells sampled are exfoliated (naturally shed) or gently brushed from the cervical surface; interference with this superficial layer reduces the quality of the sample and may contribute to false-negative results.

Understanding Your Pap Smear Results

Pap smear results are reported using the Bethesda System, a standardized terminology established in 1988 and updated in 2001 and 2014. Understanding the terminology helps women and their providers discuss next steps clearly:

NILM (Negative for Intraepithelial Lesion or Malignancy): A normal result. No abnormal cells were detected. This does not mean HPV-negative — a NILM Pap result can coexist with HPV infection. A NILM result indicates that cervical cells appeared normal under cytological examination at this time.

ASC-US (Atypical Squamous Cells of Undetermined Significance): The most common abnormal Pap result. Squamous cells show minor abnormalities that could represent early HPV effect, low-grade lesion, or benign reactive change. Management typically involves HPV reflex testing on the same sample — if HPV-negative, return to routine screening; if HPV-positive, colposcopy is recommended.

ASC-H (Atypical Squamous Cells, Cannot Exclude High-Grade SIL): Similar cellular appearance to ASC-US but with features suggesting a higher-grade lesion may be present. Colposcopy is recommended regardless of HPV status.

LSIL (Low-Grade Squamous Intraepithelial Lesion): Cellular changes consistent with mild dysplasia (CIN 1) or acute HPV cytopathic effect (koilocytosis). In most women, managed with colposcopy or 1-year repeat co-test. In women under 25, observation is preferred over colposcopy due to high rates of spontaneous regression.

HSIL (High-Grade Squamous Intraepithelial Lesion): Cellular changes consistent with moderate or severe dysplasia (CIN 2/CIN 3). Colposcopy with directed biopsy is required. This result carries a higher probability of finding CIN 2 or CIN 3 on biopsy, though not all HSIL Pap results reflect true high-grade histological lesions.

AGC (Atypical Glandular Cells): Glandular cells (endocervical or endometrial origin) that appear abnormal. Requires colposcopy plus endocervical sampling; endometrial biopsy is also recommended for women over 35 or with abnormal uterine bleeding. AGC can herald adenocarcinoma precursors of either cervical or endometrial origin.

What Happens After an Abnormal Pap Smear

An abnormal Pap smear does not mean cervical cancer is present — it means further evaluation is needed. The specific follow-up path depends on which type of abnormality was found and the patient’s prior screening history, per ASCCP 2019 risk-based management guidelines:

• ASC-US + HPV negative: Repeat co-test in 3 years; no colposcopy needed
• ASC-US + HPV positive (or HPV unknown): Colposcopy
• LSIL in women 25+: Colposcopy (or 1-year repeat acceptable)
• HSIL: Colposcopy with biopsy; some guidelines allow direct LEEP without biopsy first
• AGC: Colposcopy + endocervical sampling ± endometrial biopsy

If colposcopy and biopsy confirm CIN 2 or CIN 3, excisional or ablative treatment is recommended. After treatment, surveillance continues with co-testing at 6 months and annually for 25 years. Most women with abnormal Pap smears have pre-cancerous lesions (CIN), not invasive cancer — the Pap smear is catching problems at a stage when they are highly curable.

For a complete explanation of follow-up pathways and what to expect, see our detailed article on cervical cancer screening.

Pap Smear Frequency and Scheduling

The recommended interval for Pap smear testing depends on the screening approach chosen and the individual’s age:

• Pap smear alone (USPSTF): Every 3 years for ages 21–65 (USPSTF); every 3 years for ages 25–65 (ACS, as acceptable alternative to preferred HPV testing)
• Pap + HPV co-test: Every 5 years for ages 30–65 (USPSTF; ACS ages 25–65)
• Primary HPV testing (no Pap): Every 5 years for ages 25–65 (ACS preferred); FDA-approved option (USPSTF also allows this)
• Under age 21 (USPSTF) or under 25 (ACS): Not recommended regardless of sexual activity history
• Over age 65 with adequate prior testing: Screening can stop

Pap Smear vs. HPV Test vs. Co-Testing

Women are sometimes uncertain about the differences between a Pap smear, an HPV test, and co-testing. Here is a clear comparison:

• Pap smear: Examines cervical cells under a microscope for morphological abnormalities. Sensitivity ~55–70% for CIN 2+. Performed every 3 years. Does not directly detect HPV.
• HPV test: Detects high-risk HPV DNA in cervical cells. Sensitivity ~90–95% for CIN 2+. If negative, can be repeated every 5 years. Does not look at cell appearance.
• Co-testing: Both Pap and HPV test performed on the same sample simultaneously. Highest sensitivity. Negative result reassurance for 5 years. Recommended by USPSTF for women 30–65.

In liquid-based cytology (the standard US method), all three options can be run from the same cervical sample collected during the same clinic visit — no additional specimen collection is required to add HPV testing to a Pap smear.

Limitations of the Pap Smear

Understanding the Pap smear’s limitations helps explain why regular testing rather than a single negative result is the basis of cervical cancer prevention:

• Sensitivity ~55–70%: A single Pap smear misses up to 30–45% of significant cervical lesions. This false-negative rate is clinically manageable because the long pre-invasive phase of cervical cancer (10–15 years) means a lesion missed on one test will likely be detected on subsequent screenings — provided screening intervals are maintained.
• Less effective for adenocarcinoma: Glandular cells of the endocervical canal are harder to sample reliably; adenocarcinoma and adenocarcinoma in situ (AIS) are more effectively detected by HPV testing than by cytology alone — one reason ACS now recommends primary HPV testing as the preferred approach.
• Does not detect ovarian, endometrial, or vaginal cancer: The cervical brush samples only cells from the cervix; abnormalities elsewhere in the reproductive tract are not captured.
• Inadequate samples: Approximately 1–5% of Pap smears are reported as inadequate due to insufficient cellularity, air-drying artifacts (conventional smear), or obscuring blood/inflammation. Liquid-based cytology has reduced inadequate sample rates compared to conventional smears.

Pap Smear During Pregnancy

Cervical screening during pregnancy follows the same schedule as for non-pregnant women. If a Pap smear is overdue, it can and should be performed at the first prenatal visit. Colposcopy is safe during pregnancy if triggered by an abnormal result. Several important pregnancy-specific considerations apply:

• Excisional procedures (LEEP, cone biopsy) are generally deferred until after delivery unless invasive cancer is strongly suspected, to avoid risk of preterm birth associated with cervical excision during pregnancy
• Cervical ectropion is more prominent during pregnancy (due to elevated estrogen), making post-coital bleeding and a visually abnormal cervix more common — these do not automatically indicate pre-cancer but should be evaluated
• CIN diagnosed during pregnancy is managed conservatively with repeat colposcopy at each trimester; most CIN 2 lesions in pregnant women are managed expectantly, with definitive treatment deferred to the postpartum period

Who Does Not Need a Pap Smear

Certain groups of women do not need routine Pap smear screening:

• Women under 21 (USPSTF) or under 25 (ACS preferred): cervical cancer is rare in this age group; HPV infections typically clear spontaneously; screening generates excessive colposcopy and treatment of lesions that would have resolved
• Women over 65 with adequate prior normal testing: three consecutive normal Pap smears or two consecutive negative co-tests in the past 10 years, with the most recent test within 5 years
• Women who have undergone total hysterectomy for benign disease: the cervix is removed; no cervical tissue remains to screen
• Exception: women who had hysterectomy for CIN 3 or cervical cancer need vaginal cuff testing for 25 years post-surgery

Frequently Asked Questions

Does a Pap smear hurt?

Most women experience only mild pressure or brief cramping, primarily when the endocervical brush enters the cervical canal. The sensation is usually described as similar to mild menstrual cramps and lasts only seconds. Some women — particularly those with vaginismus, cervical stenosis (narrowing), or postmenopausal vaginal atrophy — may find speculum insertion more uncomfortable. Informing your provider in advance allows accommodations such as smaller specula, additional lubrication, and a slower technique. Some spotting afterward is normal.

Can I have a Pap smear while menstruating?

Light spotting generally will not prevent a Pap smear from being performed, though your provider will assess the sample quality. Moderate to heavy menstrual bleeding can obscure cervical cells and reduce the accuracy of the result, potentially leading to an “inadequate sample” result requiring repeat testing. If you have a choice, scheduling mid-cycle (approximately days 10–20 of a typical cycle) is preferable. If you have irregular periods or cannot predict your cycle, proceed with the appointment and let your provider decide whether to proceed or reschedule.

What does it mean if my Pap smear is inadequate?

An inadequate (or unsatisfactory) Pap result means the sample did not contain enough well-preserved cells to be analyzed reliably. This is not an abnormal result — it does not indicate pre-cancer or cancer. It simply means the test needs to be repeated, usually in 2–4 months. Common causes include thick cervical mucus, inflammation, recent sexual intercourse or douching, or insufficient sampling technique. Liquid-based cytology has substantially reduced inadequate sample rates compared to the older conventional smear method.

I had a normal Pap smear — do I still need an HPV test?

If you had a Pap smear alone and it was normal, follow your age-appropriate interval (3 years if you are 21–29; 3 years if you are 30–65 on Pap-alone screening). If you had a co-test (Pap + HPV) and both were negative, your next test can wait 5 years. If your provider offers co-testing or primary HPV testing, these options provide a longer reassurance window and are now preferred by ACS and USPSTF for women 30 and older. Discuss your screening approach with your provider to confirm the most appropriate option for your age and risk profile. For more on screening options, see our guide to cervical cancer screening and our overview of cervical cancer symptoms to know when to seek evaluation between scheduled tests.

The Evolution of Pap Smear Technology

The Pap smear has evolved substantially since Papanicolaou introduced the concept of cervical cytology. Understanding this evolution helps explain why modern Pap smears are more reliable than the test that was performed a generation ago, and why clinical guidelines have shifted toward longer intervals and HPV-based screening.

Conventional Pap smear (1940s–1990s): Cells were smeared directly onto a glass slide, fixed with hairspray or ethyl alcohol spray, and sent to the laboratory. This method was prone to air-drying artifacts (if fixation was delayed), cell clumping, and uneven cell distribution on the slide, contributing to a relatively high inadequate sample rate (5–10%) and the ~30% false-negative rate associated with the conventional method.

Liquid-based cytology (ThinPrep, introduced 1996; SurePath, 2000): Rather than smearing cells onto a slide at the point of collection, the brush and spatula are rinsed into a liquid preservative vial. At the laboratory, cells are processed (filtered or centrifuged) into a thin, uniform layer on a glass slide. Benefits include: lower inadequate sample rate (typically <1%), reduced background (blood, mucus, inflammatory cells dispersed more evenly), and — critically — the ability to use residual liquid from the same vial for HPV DNA testing, enabling co-testing without a second collection.

Computer-assisted reading (FDA-approved since 1996): FDA-approved computer systems (AutoPap, BD FocalPoint) can pre-screen slides, flagging cases that require human cytopathologist review and allowing cytopathologists to focus on the highest-risk slides. This improves throughput and reduces the false-negative rate associated with reader fatigue in high-volume cytology laboratories.

Primary HPV screening (emerging standard): The ACS 2020 updated guidelines now recommend primary HPV testing — without a Pap smear — as the preferred approach for women 25–65. This reflects evidence that HPV testing has higher sensitivity than cytology, provides a longer reassurance interval when negative (5 years), and is particularly effective at detecting adenocarcinoma precursors that cytology alone often misses. In Australia and the Netherlands, national cervical screening programs have transitioned to primary HPV testing — with cytology used as a triage test when HPV is positive — and early data confirm superior performance compared to Pap-first strategies.

The Role of the Pap Smear in a Post-Vaccination Era

With expanding HPV vaccination coverage among adolescents, a common question is whether Pap smear screening will remain necessary in the long term. The current answer is yes — for several reasons.

First, the existing adult population includes many women who were not vaccinated in adolescence and who carry unknown HPV infection history. For these women, Pap smear and HPV screening remain the primary protection against cervical cancer. Second, even Gardasil 9 — the most comprehensive current HPV vaccine — covers approximately 90% of cancer-causing HPV types, not 100%. The remaining 10% of cervical cancers caused by non-vaccine HPV types can still be caught and treated by cervical screening. Third, mathematical modeling of national cervical cancer elimination timelines (such as Australia’s projected elimination before 2030) assumes continued screening in vaccinated cohorts — without screening, elimination targets are not achievable.

In a future where near-universal HPV vaccination from adolescence is achieved across multiple decades, cervical cancer screening protocols may be able to extend intervals further or change start ages. But this is a future state; for women alive today, the Pap smear — or its HPV-testing successor — remains a critical protection against cervical cancer.