The Pap smear is a routine screening tool used to detect changes in the cells of the cervix, the lower part of the uterus that opens into the vagina. This test involves collecting a small sample of cells to examine for abnormalities that could potentially progress to cancer over many years. Receiving an abnormal result can be alarming, but it is a common occurrence that rarely signifies cancer; instead, it most often indicates the presence of precancerous cellular changes, frequently caused by the human papillomavirus (HPV). These changes require careful monitoring or intervention to prevent any future development of malignancy.
Understanding the Abnormal Result Classifications
When a Pap test identifies abnormal cells, the results are categorized using specific medical terminology to indicate the degree of change observed in the cells. These classifications are grouped into low-grade and high-grade categories, which guide the next steps for follow-up. The mildest and most frequent abnormal finding is Atypical Squamous Cells of Undetermined Significance, or ASC-US, meaning the cells look slightly irregular, but the cause is not clear.
The next level of abnormality is the Low-Grade Squamous Intraepithelial Lesion (LSIL), which indicates mild changes in the size, shape, and organization of the surface cells. LSIL is often associated with a current HPV infection and corresponds to the least severe form of precancerous change. A more serious finding is the High-Grade Squamous Intraepithelial Lesion (HSIL), where the cells show more significant and severe abnormalities. HSIL is considered a more probable precursor to cancer than LSIL, making immediate follow-up necessary.
Initial Follow-Up Testing and Monitoring
The first response to an abnormal Pap smear often involves a non-invasive procedure called reflex HPV testing, which uses the same cell sample collected for the initial Pap test. This testing is done to check for the presence of high-risk strains of the human papillomavirus, as persistent infection with these strains is the primary cause of cervical cell changes. A negative HPV test following an ASC-US result typically means the cell changes are likely due to a temporary factor, such as irritation or a minor infection, and the patient can return to routine screening.
For low-grade abnormalities like ASC-US or LSIL, especially in younger individuals, the recommendation is often “watchful waiting” or repeat Pap smears on a scheduled basis. This monitoring approach is used because the immune system can often clear the HPV infection and reverse the cellular changes on its own, a process that can take up to two years. Patients with LSIL who test negative for high-risk HPV may have a repeat Pap test and HPV co-test scheduled in one year to ensure the abnormality resolves. If the initial abnormal result was ASC-US and the HPV test is positive, or if a low-grade change persists after a year of monitoring, more direct examination becomes necessary.
Advanced Diagnostic Procedures
If the initial monitoring shows that a low-grade abnormality is persistent, or if the Pap smear immediately suggests a high-grade abnormality (HSIL), an advanced diagnostic procedure called a Colposcopy is typically performed. This is an in-office procedure where a specialized instrument with a magnifying lens is used to allow the clinician to closely examine the surface of the cervix. During the Colposcopy, a mild acetic acid solution is applied to the cervix, which temporarily turns abnormal areas white, making them clearly visible for evaluation.
If the Colposcopy identifies suspicious areas, small tissue samples, known as biopsies, are collected from the cervix and sent to a lab for definitive diagnosis. The lab results of these biopsies are classified as Cervical Intraepithelial Neoplasia (CIN) and graded on a scale from 1 to 3, with CIN 1 being the mildest change and CIN 3 being the most severe precancerous change. CIN 1 corresponds to a low-grade abnormality and often resolves spontaneously, while CIN 2 and CIN 3 represent moderate to severe high-grade changes that carry a higher risk of progressing to cancer if left untreated. The Colposcopy and subsequent biopsy are the necessary steps to accurately determine the severity of the precancerous changes and decide whether treatment is required.
Treatment for Confirmed Cellular Changes
Once the biopsy confirms a high-grade cellular change, such as CIN 2 or CIN 3, treatment is usually recommended to remove the precancerous tissue and prevent the development of cervical cancer. The most common therapeutic procedure is the Loop Electrosurgical Excision Procedure, or LEEP, which is typically performed in an outpatient setting using a local anesthetic. This procedure utilizes a thin wire loop heated by an electrical current to precisely excise, or cut away, the abnormal area of tissue from the cervix.
Other methods, such as Cryotherapy, which uses extreme cold to destroy abnormal cells, or a Cold Knife Cone Biopsy, a surgical procedure that removes a cone-shaped piece of tissue, may also be used in specific cases. The tissue removed during a LEEP is sent to a pathologist to ensure the margins, or edges, of the sample are clear of abnormal cells, indicating a complete excision. Following the procedure, close surveillance with repeat Pap and HPV testing is necessary to ensure the abnormal cells do not return.