Cervical cytology is the microscopic examination of cells collected from the cervix, the lower, narrow end of the uterus that opens into the vagina. This study is primarily used as a screening tool for the early detection of abnormal changes that could potentially develop into cervical cancer. Identifying these cellular changes allows practitioners to intervene before cancer begins, a process that has significantly reduced mortality rates. The Papanicolaou test, or Pap test, gathers a representative sample of cells for laboratory analysis.
The Role of the Pap Test in Screening
The Papanicolaou test collects cells from the cervix for screening. During a pelvic examination, a healthcare professional uses a speculum to gently separate the vaginal walls, allowing the cervix to be seen. A small brush and spatula are then used to collect cells from both the outer surface and the canal of the cervix. The collection process is quick and generally causes only minor pressure or cramping.
The primary purpose of the Pap test is the early detection of cell changes caused by the human papillomavirus (HPV), which causes most cervical cancers. Screening generally recommends starting around age 21. For those aged 21 to 29, a Pap test alone is recommended every three years.
After age 30, screening options broaden to include co-testing, combining a Pap test with an HPV test every five years. Primary HPV testing every five years for individuals aged 25 to 65 is also recommended, with co-testing or Pap-only testing remaining acceptable alternatives. Screening can typically stop after age 65 if a person has a history of consistently normal results.
Sample Processing and Laboratory Methods
Once the cells are collected, the sample is sent to a specialized laboratory for processing and microscopic review. Historically, the conventional Pap smear involved spreading the collected cells directly onto a glass slide. This technique often resulted in clumping, cellular overlap, and obscured cells due to blood or mucus, making interpretation difficult.
Today, the more common method is liquid-based cytology (LBC). With LBC, the collection device is rinsed into a vial of preservative liquid, allowing the laboratory to remove obscuring materials and create a thinner, more uniform layer of cells on the slide. This improved preparation reduces the rate of unsatisfactory samples and increases the clarity of cellular details.
A major advantage of LBC is that the remaining cell suspension can be used for ancillary testing, such as for high-risk HPV, without needing a separate sample collection. Cytotechnologists often use automated screening systems to review the prepared slides. The final diagnosis is then made by a trained cytopathologist or cytotechnologist using the standardized Bethesda System.
Decoding Cytology Classifications
The results of cervical cytology are reported using the standardized Bethesda System, which uses specific terminology. The most common result is Negative for Intraepithelial Lesion or Malignancy (NILM), which indicates that the cells are normal and there is no evidence of precancerous or cancerous changes.
An abnormal result may fall into the category of Atypical Squamous Cells of Undetermined Significance (ASCUS). This is a common finding where the cells show minor changes that are not definitive enough to be classified as a true lesion. ASCUS often prompts reflex HPV testing to determine the risk level. More significant findings are classified as Squamous Intraepithelial Lesions (SILs), which are divided into two grades.
Low-Grade Squamous Intraepithelial Lesion (LSIL)
LSIL typically indicates mild dysplasia and is often associated with an active HPV infection. These changes are considered mild and frequently resolve on their own.
High-Grade Squamous Intraepithelial Lesion (HSIL)
HSIL represents moderate to severe dysplasia. HSIL carries a higher risk of progressing to invasive cancer if left untreated, requiring immediate follow-up.
A less common classification is Atypical Glandular Cells (AGC), which indicates abnormal cells from the glandular tissue lining the inner cervix or the uterus. AGC can signal a more serious problem and always requires further investigation.
Management of Abnormal Findings
Clinical management following an abnormal Pap test result is determined by the specific classification and the individual’s HPV status. Management protocols are risk-based, aiming to avoid overtreatment for minor, self-resolving changes while ensuring that high-risk lesions are addressed promptly.
For mild abnormalities like ASCUS and LSIL, the next step often involves repeat testing after six to twelve months, or immediate HPV testing to triage the risk. If high-risk HPV is not present, the patient often returns to routine screening, as the cell changes are likely to clear spontaneously.
If the HPV test is positive, or if the abnormality is more severe, such as HSIL or AGC, the patient is typically referred for colposcopy. Colposcopy is an in-office procedure where a provider uses a magnifying instrument to visually examine the cervix after applying a solution to highlight abnormal areas. If a concerning area is visualized, a small tissue sample (biopsy) is taken for definitive diagnosis. If the biopsy confirms a high-grade precancerous lesion, treatment procedures are performed to remove the abnormal tissue.
Treatment Options
The most common treatment is the Loop Electrosurgical Excision Procedure (LEEP), which uses a thin wire loop heated by an electrical current to remove the affected area. Another ablative option is cryotherapy, which uses a specialized cold probe to freeze and destroy the abnormal cells. Both LEEP and cryotherapy are effective treatments for precancerous cells.