The Papanicolaou test, commonly known as a Pap smear, serves as a preventative screening tool for cervical cancer. The procedure involves collecting cells from the cervix to examine them under a microscope for changes that could develop into cancer over time. An abnormal result indicates that some cells collected from the cervix appear unusual, but this finding does not automatically mean cancer is present. The purpose of the screening is to detect these cellular changes at an early, treatable stage, which significantly increases the chance of a successful outcome.
The Central Role of Human Papillomavirus (HPV)
The overwhelming majority of clinically significant abnormal Pap smears are caused by the Human Papillomavirus (HPV). HPV is a highly common sexually transmitted infection, with nearly all sexually active individuals acquiring it at some point. The virus has over 150 different types, but only a small number are classified as high-risk and cause pre-cancerous cellular changes.
High-risk types, particularly HPV 16 and HPV 18, are responsible for approximately 70% of all cervical cancer cases globally. While most HPV infections are transient and clear up naturally through the body’s immune response, a persistent infection with a high-risk strain leads to problems. The virus invades basal epithelial cells and produces oncoproteins (E6 and E7) that interfere with the cell’s natural growth regulators.
This interference disrupts the normal cell cycle, promoting uncontrolled proliferation. This cellular change, known as dysplasia, is the precursor to cervical cancer. An abnormal Pap smear often indicates that a persistent, high-risk HPV infection is altering the cellular structure of the cervix.
Other Non-Viral Factors Leading to Abnormal Readings
Not every abnormal Pap smear result is linked to persistent high-risk HPV or pre-cancerous changes. Many minor abnormalities are transient and caused by inflammation or irritation of the cervical tissue. Infections like bacterial vaginosis (BV), yeast infections, or trichomoniasis can cause cervical cells to appear atypical.
These common infections trigger an inflammatory response, which alters the appearance of the cells. Hormonal changes also influence results, particularly in post-menopausal individuals where decreased estrogen can lead to cervical atrophy. Cells may appear atypical due to tissue dryness and thinning.
Technical factors during sample collection or processing can lead to an “unsatisfactory” or atypical reading. If the sample contains too few cells, or is obscured by blood or mucus, the laboratory cannot provide a definitive result. In these non-viral cases, treating the underlying infection or retesting often results in a return to normal readings.
Understanding the Classification of Abnormal Cells
Abnormal Pap smear results are categorized using standardized terminology reflecting the degree of cellular change. The least worrisome finding is Atypical Squamous Cells of Undetermined Significance (ASC-US), where cells look slightly abnormal, but the cause is unclear (infection or HPV). Low-Grade Squamous Intraepithelial Lesion (LSIL) suggests mild cellular changes (mild dysplasia), usually caused by HPV, which often resolves spontaneously.
A more serious finding is High-Grade Squamous Intraepithelial Lesion (HSIL), which represents moderate to severe dysplasia. These cells have pronounced abnormalities and are less likely to clear without intervention, carrying a greater risk of progressing to cancer if left untreated. Atypical Squamous Cells, Cannot Exclude HSIL (ASC-H) indicates an abnormality raising suspicion for HSIL, requiring immediate follow-up.
Atypical Glandular Cells (AGC) refers to abnormal changes in the glandular cells of the endocervix or uterus, rather than the surface squamous cells. Since glandular changes are difficult to assess, an AGC result necessitates a more extensive workup to rule out a serious condition higher in the reproductive tract. The specific classification guides the appropriate next steps for monitoring or treatment.
Follow-up Procedures After an Abnormal Result
Follow-up depends on the specific classification of the abnormal Pap smear result, the patient’s age, and HPV status. For a minor abnormality like ASC-US, the provider may recommend a repeat Pap smear in twelve months or an HPV co-test to determine if a high-risk strain is present. If the result is LSIL, or if a high-risk HPV strain is detected, a colposcopy is typically the next step.
A colposcopy is a procedure where the cervix is examined using a specialized magnifying instrument (the colposcope). A mild vinegar solution is applied to highlight abnormal areas. If suspicious tissue is identified, a small tissue sample (biopsy) is taken for laboratory analysis. Low-grade lesions are frequently managed with a “watch and wait” approach, as they often regress naturally.
Confirmed high-grade lesions (HSIL) require treatment to remove the abnormal cells and prevent cancer progression. Common removal procedures include the Loop Electrosurgical Excision Procedure (LEEP), which uses a heated wire loop to shave off affected tissue, or cryotherapy, which freezes the abnormal cells. These targeted procedures effectively remove the pre-cancerous cells while preserving healthy cervical tissue.