A Pap smear tests for abnormal cell changes on your cervix that could indicate precancer or cervical cancer. It does not test for STIs, ovarian cancer, or uterine cancer, which is a common source of confusion. The test is specifically designed to catch cellular changes early, often years before they would ever become cancerous, making it one of the most effective cancer screening tools available.
What a Pap Smear Actually Detects
A Pap smear is a cytology test, meaning it examines individual cells under a microscope. During the test, a clinician collects cells from two areas of your cervix: the outer surface (ectocervix) using a small plastic spatula, and the inner canal (endocervix) using a tiny brush. The key target is the transformation zone, the area where two types of cervical cells meet. This is where the vast majority of cervical abnormalities develop.
The cells are sent to a lab, where a pathologist classifies them using a standardized system called the Bethesda System. Results fall into a few main categories:
- Normal (NILM): No abnormal cells found. This is the result most people get.
- ASC-US: Atypical squamous cells of undetermined significance. The cells look slightly unusual but not clearly abnormal. This is the most common “abnormal” result and is often caused by temporary irritation or a low-risk HPV infection.
- LSIL: Low-grade squamous intraepithelial lesion. The cells show mild changes, typically linked to an HPV infection. Many LSIL findings resolve on their own without treatment.
- HSIL: High-grade squamous intraepithelial lesion. The cells show moderate to severe changes that could become cervical cancer if left untreated. This result usually leads to further testing.
- AGC: Atypical glandular cells. These abnormal cells come from the glandular tissue of the cervix or uterus. Because glandular abnormalities can signal more serious problems, this result almost always triggers a follow-up procedure.
In rare cases, a Pap smear can detect cells from endocervical adenocarcinoma (cancer of the glandular cells lining the cervical canal) or endometrial adenocarcinoma (cancer of the uterine lining), though it is not designed to screen for the latter.
The HPV Connection
HPV testing and Pap smears are closely related but are not the same test. A Pap smear looks at how your cells appear under a microscope. An HPV test checks the same cell sample for the DNA of high-risk strains of human papillomavirus, the virus responsible for nearly all cervical cancers.
Both tests can be done from a single collection during the same office visit, which is why many people assume they’re one test. For women aged 30 to 65, the preferred screening method is now a primary HPV test every five years, or co-testing (Pap plus HPV) every five years. For women aged 21 to 29, a Pap test alone every three years is recommended, since HPV infections in younger women are extremely common and usually clear on their own.
What a Pap Smear Does Not Test For
This is where the biggest misunderstandings happen. A Pap smear does not screen for sexually transmitted infections like chlamydia, gonorrhea, syphilis, herpes, or HIV. Years ago, chlamydia screening was often done from a cervical sample collected at the same time as a Pap, which led many people to believe the Pap itself covered STIs. Public health guidelines have stressed the separation of these two types of screening for over a decade. STI testing now typically uses a urine sample or vaginal swab, no pelvic exam required.
A Pap smear also cannot reliably detect ovarian cancer. While ovarian cancer cells could theoretically travel from the ovaries through the fallopian tubes and uterus to the cervix, this is extremely rare. There is currently no routine screening test for ovarian cancer. Similarly, the Pap is not a screening tool for endometrial (uterine) cancer, though abnormal endometrial cells occasionally show up incidentally.
How Accurate Is It?
A single Pap smear catches high-grade cervical lesions about 55% to 80% of the time. That might sound low, but the test is designed to be repeated at regular intervals, so abnormalities missed on one screening are typically caught on the next. When looking specifically at moderate to severe cell changes, the test’s specificity is around 95%, meaning it rarely flags something as abnormal when it isn’t. Adding HPV testing improves detection rates significantly, which is why co-testing or primary HPV testing is now preferred for women over 30.
What Happens After an Abnormal Result
An abnormal Pap result does not mean you have cancer. Most abnormal results reflect minor cell changes that resolve without treatment. What happens next depends on the type and severity of the abnormality.
For ASC-US results, you may simply be asked to return for a repeat test in one to three years, or your sample may be tested for HPV to determine if closer follow-up is needed. LSIL results in younger women are often monitored with repeat screening, since the underlying HPV infection frequently clears on its own.
Results of HSIL, ASC-H (atypical cells that may be high-grade), AGC, or adenocarcinoma in situ typically lead to a colposcopy. During this procedure, a clinician uses a magnifying instrument to examine your cervix more closely and usually takes a small tissue biopsy. The biopsy provides a definitive diagnosis and guides treatment decisions. The colposcopy itself takes about 10 to 20 minutes and may cause mild cramping similar to a period cramp.
How to Prepare for the Test
For the most accurate results, avoid sexual intercourse, douching, and any vaginal medicines, foams, or spermicidal products for two days before your appointment. These can wash away or obscure the cells the test needs to examine. Try to schedule your Pap for a time when you’re not on your period, though the test can still be performed during menstruation if needed. If you’re experiencing bleeding that isn’t part of your regular cycle, don’t delay your appointment.
The test itself takes only a few minutes. A speculum is inserted to hold the vaginal walls open, and cells are gently collected from the cervix with a spatula and brush. Most people feel brief pressure or mild discomfort, but not pain.