Pap smears and HPV testing

Cervical screening works better than almost any other cancer screening we have, because the disease it targets passes through a long, detectable precancerous stage before it becomes cancer. The aim is not to find cervical cancer but to find the abnormal cells that precede it by years, when removing them ends the matter. What has changed over the last decade is how we test, how often, and how results are acted on. The test itself still takes about two minutes.

What the test looks for, and what it does not

A Pap smear collects cells from the surface of the cervix and from the canal just inside it. Those cells are examined for the changes produced by persistent infection with high risk human papillomavirus, the virus responsible for effectively all cervical cancer. Because those changes typically take years to progress, screening at intervals catches them while they are still confined to the surface layer and can be removed in an office procedure.

The limits are worth stating plainly. A Pap does not screen for ovarian cancer, and no reliable screening test for ovarian cancer exists for average risk women. It is not a test for chlamydia, gonorrhea or any other sexually transmitted infection; those need separate swabs or urine testing, which can be done at the same visit. It does not assess the lining of the uterus, so postmenopausal bleeding or persistently abnormal bleeding requires its own evaluation regardless of a normal Pap.

Cytology, primary HPV testing and co-testing

Three approaches are in use. Cytology, the classic Pap, examines cell morphology under a microscope and reports what the cells look like. Primary HPV testing looks instead for the DNA of high risk HPV types and reports whether the infection that causes the disease is present. Co-testing runs both on the same sample.

HPV testing is the more sensitive of the two. It detects a higher proportion of significant precancer, and a negative HPV result predicts a very low risk for several years, which is what makes longer intervals safe. Cytology is more specific in the short term, meaning fewer positive results that turn out to be nothing. The trade-off is real: HPV based screening finds more disease but also flags more transient infections that would have cleared on their own, which means more follow up visits and more anxiety for some women. Most guideline bodies have judged the sensitivity worth it, and the US Preventive Services Task Force has moved toward primary HPV testing as the preferred approach from age 30, including options for self collected samples. The collection procedure feels identical from your side.

How often to screen, and when to stop

Intervals depend on your age and on which test is used. For a woman with no history of abnormal results, no immune compromise and no in utero DES exposure, current United States practice looks like this.

• Under 21: no cervical screening, whatever your sexual history
• Ages 21 to 29: cytology alone every 3 years
• Ages 30 to 65: primary HPV testing every 5 years, co-testing every 5 years, or cytology alone every 3 years
• Over 65: screening can stop given an adequate record of recent negative results and no history of high grade abnormality
• After hysterectomy with removal of the cervix for benign reasons: no further screening
• After treatment for high grade precancer: closer surveillance continues for at least 25 years

Those intervals assume a clean history. Previous CIN 2 or CIN 3, HIV or other immunosuppression, or an organ transplant puts you on a different and closer schedule, and we will tell you that explicitly rather than leaving you to work it out from a chart.

What an abnormal result means

Abnormal Pap results are common, and the large majority are not precancer and are nowhere near cancer. The report uses a specific vocabulary, and knowing what the terms mean removes most of the alarm they cause.

ASC-US and LSIL

ASC-US means atypical squamous cells of undetermined significance: the cells look slightly off and the pathologist cannot say whether that reflects HPV, inflammation or nothing at all. It is the most frequent abnormal result. LSIL, low grade squamous intraepithelial lesion, is the cellular signature of an active HPV infection. In younger women both commonly resolve without treatment as the immune system clears the virus. Management turns on the HPV result attached to the sample: HPV negative usually means returning to routine or slightly shortened intervals, while HPV positive, particularly types 16 or 18, generally leads to colposcopy.

HSIL, ASC-H and AGC

HSIL, high grade squamous intraepithelial lesion, is genuine precancer and warrants colposcopy promptly. In selected situations, particularly where the estimated risk of underlying CIN 3 is very high and childbearing is complete, immediate treatment without a preliminary biopsy is an accepted option. ASC-H means the pathologist cannot exclude a high grade lesion and is handled with the same urgency. AGC, atypical glandular cells, is uncommon and deserves particular attention because the cells may arise from the endocervical canal or from the uterine lining; evaluation includes colposcopy with sampling of the canal, plus endometrial sampling if you are over 35 or have abnormal bleeding.

What happens next

Follow up is now driven by estimated risk rather than by the result label alone. The ASCCP risk based guidelines combine your current result, your HPV status and your screening history to estimate the chance that high grade precancer is present, and that estimate determines whether you repeat testing in a year, return in three, proceed to colposcopy, or go straight to treatment. One consequence is that the same Pap result can produce different recommendations in two different women. That is intentional, not inconsistency.

An abnormal Pap is a signal to look more closely. It is not a diagnosis of cancer.

Colposcopy is an office procedure. The cervix is examined under magnification after a dilute acetic acid solution is applied, which makes abnormal areas visible, and any suspicious area is biopsied. It takes a few minutes and feels like a period cramp for most women. If biopsy confirms high grade precancer, treatment usually means removing the affected zone of the cervix, most often by LEEP, performed in the office under local anesthesia and highly effective. Low grade findings are generally monitored rather than treated, because treating tissue that would have cleared on its own carries costs of its own, including a small effect on future pregnancies.

Where the guidelines disagree

There is honest disagreement about when screening should start. Professional bodies in obstetrics and gynecology continue to recommend beginning at 21, while the American Cancer Society recommends starting at 25, on the grounds that HPV vaccination has reduced disease in younger women and that screening in the early twenties turns up many abnormalities that would have resolved without intervention. Both positions are defensible on the evidence. Self collection is also moving quickly, and it matters most for women who avoid speculum examinations altogether.

Vaccination changes the background but not, so far, the schedule. HPV vaccination is routine at 11 or 12, can be given from 9, and is approved through 45 as a shared decision for adults who missed it earlier. Vaccinated women still screen on the standard schedule, because the vaccine does not cover every oncogenic type and may have been given after exposure had already occurred.