A smear test, commonly known as a Pap test or Pap smear, is a medical procedure that involves collecting cells for microscopic examination. The Papanicolaou test, named after its inventor, George Papanicolaou, is the specific cervical screening method that the general public most often associates with the “smear test.” This procedure focuses on cells gathered from the cervix, the lower, narrow end of the uterus that opens into the vagina. The purpose of this routine screening is to detect changes in the cervical cells, which are often the earliest signs of potential disease.
The Purpose of Cervical Screening
The primary function of the Pap test is to serve as a screening tool to prevent the development of cervical cancer. This test does not diagnose cancer outright but identifies precancerous cell changes, known as dysplasia, on the surface of the cervix. Detecting these cellular abnormalities early allows for preventative treatment before cancerous development can occur.
Nearly all cases of cervical cancer are linked to long-term infection with high-risk types of the Human Papillomavirus (HPV). HPV is a common sexually transmitted infection that causes the cellular changes the Pap test is designed to find. Because of this strong link, modern cervical screening often involves co-testing, performing both a Pap test and an HPV test on the same collected sample, especially for individuals over age 30.
The HPV test looks specifically for the presence of the viral DNA known to cause cervical changes. This co-testing strategy offers a more comprehensive assessment of a person’s risk. An abnormal Pap result combined with a positive high-risk HPV test indicates a higher need for follow-up. When precancerous changes are found and treated, the progression to invasive cancer is prevented over 95% of the time.
The Pap Test Procedure
The Pap test procedure begins in a healthcare setting with the patient positioned for a pelvic examination. A plastic or metal instrument called a speculum is gently inserted into the vagina to hold the walls open, allowing the healthcare provider a clear view of the cervix. The provider then uses specialized collection tools to gather cells from the transformation zone, the area of the cervix where precancerous changes most commonly occur.
The cell collection is typically performed using a small brush, a spatula, or a combination device, which is rotated gently against the cervical surface to gather a sample of cells. While the older, conventional method involved immediately smearing the collected cells onto a glass slide, the current standard is Liquid-Based Cytology (LBC). With LBC, the collection device is rinsed or its head is snapped off into a vial containing a preservative liquid.
This vial is sealed and transported to a specialized laboratory for analysis. In the lab, the liquid sample is processed to remove obscuring materials like blood or mucus, resulting in a cleaner, more uniform layer of cells. The cells are then transferred onto a glass slide and stained using the Papanicolaou staining method. This method uses different colored dyes to make the cell structures visible under a microscope. A cytotechnologist or pathologist examines the slide for any abnormal cell shapes, sizes, or arrangements that indicate precancerous or cancerous conditions.
Interpreting Smear Results
The results of a Pap test are reported using the Bethesda System, which categorizes the findings along a spectrum. A “Normal” or “Negative for Intraepithelial Lesion or Malignancy” result means the cervical cells appeared healthy and showed no signs of precancerous changes. This result means the person should continue with routine screening at the recommended interval.
When results are reported as “Abnormal,” it indicates that cell changes, or dysplasia, were found, but this seldom means immediate cancer. One of the most frequent abnormal results is Atypical Squamous Cells of Undetermined Significance (ASCUS), meaning the cells look slightly abnormal but the cause is not clear. A Low-grade Squamous Intraepithelial Lesion (LSIL) indicates mild changes often caused by a current HPV infection, which frequently resolve on their own, especially in younger individuals.
More significant findings include High-grade Squamous Intraepithelial Lesion (HSIL), which represents more serious, moderate-to-severe changes. These changes have a higher likelihood of progressing to cancer if left untreated. For any abnormal result, the necessary follow-up depends on the severity of the findings, the patient’s age, and their HPV status. Low-grade abnormalities like ASCUS or LSIL may only require repeat testing after six to twelve months.
A finding of HSIL, or persistent low-grade changes, typically leads to a referral for a colposcopy. During a colposcopy, the doctor uses a specialized magnifying instrument to closely examine the cervix and may take a small tissue sample, called a biopsy, for a more definitive diagnosis. This subsequent step confirms the extent of the cellular changes and determines the most appropriate preventative treatment, which may involve removing the abnormal tissue.