Human papillomavirus (HPV) is a very common sexually transmitted infection that can lead to cervical cancer in some cases. Many people wonder whether HPV would be detected during a routine Pap smear test. The short answer is yes – HPV can be detected on a Pap smear if the pathologist specifically looks for signs of it. However, the main purpose of a Pap smear is to check for abnormal cervical cells that could indicate early signs of cancer. Let’s take a deeper look at how Pap smears work and the role of HPV testing.
What is a Pap Smear?
A Pap smear, also known as a Pap test, is a screening procedure for cervical cancer. It was named after Dr. George Papanicolaou, the creator of the test. The test involves collecting cells from the surface of the cervix and examining them under a microscope. The main goal is to check for abnormal or precancerous cells called dysplasia or cervical intraepithelial neoplasia (CIN).
During a Pap smear, the doctor inserts a speculum into the vagina to open it up and uses a small brush or spatula to gently scrape cells from the cervix. The collected sample of cells is then sent to a laboratory for analysis. A cytotechnologist will examine the cells under a microscope to see if any abnormalities are present.
What Abnormalities Can Be Detected?
A Pap smear can detect the following abnormalities:
- Atypical squamous cells (ASC): irregular squamous cells
- Low-grade squamous intraepithelial lesion (LSIL): mild dysplasia
- High-grade squamous intraepithelial lesion (HSIL): moderate/severe dysplasia
- Squamous cell carcinoma: cancer of the cervix
Detecting precancerous changes like LSIL allows early treatment before potential progression to cervical cancer. Important to note is that HPV infection itself does not get diagnosed on a routine Pap smear – additional HPV testing is required (more on this later).
What is HPV?
HPV stands for human papillomavirus. It is a very common sexually transmitted infection that can infect the genitals, mouth, throat, and other areas. There are over 150 known types of HPV viruses. Different HPV strains are categorized as either low-risk or high-risk based on their potential to cause cancer.
Low-Risk HPV Types
Low-risk HPV types, such as HPV 6 and 11, can cause benign genital warts. They have a low cancer risk.
High-Risk HPV Types
High-risk HPV types, such as HPV 16 and 18, can lead to cell changes that may progress to cancer over time. HPV 16 and 18 are responsible for 70% of cervical cancers. Other high-risk types include HPV 31, 33, 45, 52, and 58.
Many people contract HPV at some point. Most HPV infections resolve spontaneously and do not lead to cancer. However, high-risk HPV can persist in some individuals and cause precancerous cervical lesions. Screening tests like Pap smears aim to detect these lesions early.
Can a Pap Smear Detect HPV?
The main purpose of a traditional Pap smear is to screen for abnormal cervical cells, not to test for HPV itself. However, there are often cell changes that occur due to an active HPV infection that the pathologist can identify.
When examining Pap smear cells under a microscope, signs of HPV infection can include:
- Koilocytes: irregularly-shaped cells with halos around the nuclei
- Dyskeratosis: abnormal keratinization of squamous cells
- Atypical parakeratosis: nuclei retained in surface cells
- Binucleation and multinucleation of cells
So in a way, HPV can be detected indirectly on a Pap smear through associated cellular changes. However, cellular changes alone do not allow typing of the specific HPV strain. The pathologist simply sees abnormalities suggesting the presence of HPV.
HPV Testing Methods
To diagnose active HPV infection, specific molecular testing is required. There are two main methods:
1. HPV DNA Testing
This test detects the presence of HPV DNA in cervical cells. It can identify whether the HPV type is high-risk or low-risk, but does not specify the exact subtype. HPV DNA testing is often used adjunctively with Pap smears in women 30 years or older.
2. HPV Genotyping
HPV genotyping identifies the specific high-risk HPV types present, such as HPV 16 or 18. It detects the DNA of individual strains. HPV genotyping provides more information but is not routinely performed.
An HPV test using one of the above methods may be ordered if Pap smear results are abnormal or if HPV testing is due for a patient based on screening guidelines. Standalone HPV testing is also an approved primary cervical cancer screening approach for some women 30 and over.
HPV Testing Guidelines
Professional medical organizations provide the following guidelines on HPV testing:
Women Ages 21-29
- No screening for HPV alone – HPV testing is not recommended.
- Pap smear every 3 years.
Women Ages 30-65
- Pap smear every 3 years.
- HPV testing with Pap smear (called co-testing) every 5 years is preferred.
- HPV testing alone every 5 years is also approved.
Women Over 65
- Stop screening at age 65 if prior tests are normal and no history of abnormal results.
- Continue routine Pap smear screening for at least 20 years after serious abnormal result.
So in summary, HPV testing is not indicated for younger women but is incorporated into cervical cancer screening for women 30 and older.
How Accurate is HPV Testing Compared to Pap Smears?
HPV testing is more sensitive at detecting HPV infections that can lead to cancer compared to Pap smear screening alone. However, HPV testing also has a higher false positive rate since many infections clear on their own.
Some key statistics on the accuracy of HPV testing:
- Sensitivity of high-risk HPV DNA testing for detecting CIN2+ (pre-cancer): 96-100%
- Specificity of high-risk HPV DNA testing: 88-90%
- Pap smear sensitivity for detecting CIN2+: 60-80%
- Pap smear specificity: 86-100%
HPV tends to detect more potential problems, but further triage is needed to determine which cases require treatment versus just monitoring. The high negative predictive value of HPV testing provides assurance that cancer risk is low with a negative test.
Advantages of HPV Testing
- Finds more precancerous changes than Pap smear alone
- Longer screening intervals possible when combined with Pap smear
- High negative predictive value
Disadvantages of HPV Testing
- Does not detect all precancerous changes
- Higher false positives compared to Pap smear
- Does not determine cancer risk from specific HPV strain
- Does not replace need for regular Pap smears
Overall, HPV and Pap testing together provide a comprehensive approach to detecting both early HPV infection and any abnormal cervical changes.
HPV Vaccination
Vaccination provides the best protection against HPV infection. The CDC recommends routine HPV vaccination at age 11-12 for both boys and girls. Catch-up vaccination is recommended for females up to age 26 and males up to age 21.
The HPV vaccine protects against high-risk HPV types 16 and 18 that cause most cancers. It also protects against types 6 and 11 that cause 90% of genital warts.
Widespread vaccination has led to a major decline in HPV infections and precancerous cervical lesions. However, screening is still crucial to detect any abnormalities that could develop into cancer. Even vaccinated individuals should follow the recommended cervical cancer screening guidelines.
HPV Vaccines
There are currently three HPV vaccines approved:
- Gardasil: Quadrivalent vaccine protecting against HPV types 6, 11, 16, and 18.
- Gardasil 9: Nine-valent vaccine protecting against HPV types 6, 11, 16, 18, 31, 33, 45, 52, and 58.
- Cervarix: Bivalent vaccine protecting against HPV types 16 and 18.
The vaccines require a series of shots for full protection. Gardasil 9 offers the broadest coverage against carcinogenic HPV types and is the preferred vaccine today.
Conclusion
In summary, HPV can be detected indirectly on a Pap smear when cervical cell abnormalities related to the infection are seen. However, specific HPV testing is needed to identify active high-risk HPV infection. HPV DNA testing and Pap smears together improve early detection of cervical cancer precursors. HPV vaccination combined with routine screening provides optimal protection for women’s health.
