An abnormal result from a Papanicolaou (Pap) test often triggers immediate worry about cancer, but this reaction is generally disproportionate to the actual risk. The Pap test is a screening tool designed to detect subtle changes in cervical cells long before cancer could develop. An abnormal result is relatively common, occurring in about 5% of all Pap tests in the United States, and in the vast majority of these cases, the finding does not signify cancer. The result simply indicates the presence of cells that look unusual and requires a follow-up plan to determine the nature and severity of those changes.
Understanding Cell Changes
When a Pap test is abnormal, cells are classified based on how much they deviate from a healthy appearance, defining a spectrum of severity. The mildest and most common finding is Atypical Squamous Cells of Undetermined Significance (ASC-US). This result indicates that some cells look slightly irregular, but the cause is unclear. This irregularity could be due to inflammation, infection, or hormonal changes, not necessarily a precancerous condition.
Moving up the scale are Low-Grade Squamous Intraepithelial Lesions (LSIL) and High-Grade Squamous Intraepithelial Lesions (HSIL). These categories reflect a higher likelihood of an underlying precancerous condition called Cervical Intraepithelial Neoplasia (CIN). LSIL typically corresponds to CIN 1, where abnormal cells affect only the lower third of the cervix’s surface layer. CIN 1 lesions are the most minor form of precancerous change and often resolve on their own without intervention.
High-Grade Squamous Intraepithelial Lesions (HSIL) are more serious and generally correspond to CIN 2 or CIN 3. In CIN 2, cell changes affect up to two-thirds of the cervical lining, while CIN 3 indicates severe changes affecting more than two-thirds of the epithelium. Even CIN 3 is a form of precancer, meaning the cells are highly abnormal but have not yet invaded the deeper underlying tissue. The progression from these high-grade changes to actual invasive cancer is typically a slow process, often taking many years.
The Connection to Human Papillomavirus
The vast majority of abnormal cervical cell changes are traced back to a persistent infection with the Human Papillomavirus (HPV). HPV is the most common sexually transmitted infection globally, and most sexually active people contract at least one strain. The body’s immune system successfully clears most HPV infections naturally, often within one to two years, before lasting cell changes occur.
The concern arises when the infection involves high-risk HPV types, such as HPV 16 and 18, and the immune system fails to clear it. These high-risk strains are responsible for nearly all cases of cervical cancer. When a high-risk HPV infection persists for many years, the virus’s proteins interfere with the normal growth cycle of the cervical cells, leading to the abnormalities identified on the Pap test.
Low-risk HPV types, which can cause genital warts, are not associated with cervical cancer development. The key difference between a transient infection and one that leads to precancerous lesions is the persistence of the high-risk virus. A persistent infection creates the environment where the cellular changes, or dysplasia, can slowly progress from low-grade to high-grade lesions. Understanding that HPV is the root cause helps shift the focus from a cancer diagnosis to the management of a common viral infection and its potential cellular effects.
Your Follow-up Plan
The recommended follow-up for an abnormal Pap result depends on the degree of cell change and the patient’s HPV status, following risk-based management guidelines. For the mildest abnormality (ASC-US) or low-grade changes (LSIL), especially in younger individuals, the initial approach is often watchful waiting. Since these low-grade changes frequently resolve as the immune system clears the HPV infection, a repeat Pap or HPV test is typically scheduled in 6 to 12 months.
If follow-up testing indicates a persistent abnormality or if the initial result showed severe changes such as HSIL, the next step is usually a colposcopy. This is an office procedure where a healthcare provider uses a magnifying instrument to examine the cervix closely and applies a solution to highlight abnormal areas. During this examination, small tissue samples, or biopsies, are taken from suspicious areas to confirm the diagnosis and determine the precise grade of the precancerous lesion.
If the biopsy confirms a high-grade lesion (CIN 2 or CIN 3), treatment is recommended to remove the abnormal tissue and prevent the development of cancer. Common treatment options include the Loop Electrosurgical Excision Procedure (LEEP) or cryotherapy. LEEP uses a thin, electrified wire loop to precisely shave off the affected tissue, while cryotherapy uses a freezing probe to destroy the abnormal cells. These procedures are highly effective, curative interventions.