Cervical Cancer Screening: Pap Smear and HPV Testing
Understanding Cervical Cancer
Cervical cancer is a cancer that develops in the cervix—the lower part of the uterus that connects to the vagina. It is one of the most preventable cancers in women because it typically develops slowly over many years, passing through precancerous stages before becoming invasive cancer.
With appropriate screening and follow-up, cervical cancer can often be detected early or prevented altogether.
What Causes Cervical Cancer?
The vast majority of cervical cancers are caused by persistent infection with high-risk types of human papillomavirus (HPV).
HPV types 16 and 18 are the most common and account for over 70% of cervical cancers worldwide. Other high-risk HPV types include 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, and 68.
HPV is extremely common, transmitted through sexual contact and often cleared naturally by the immune system. However, in some women, high-risk HPV persists, leading to cellular changes in the cervix that may progress over time.
Other factors that increase the risk of cervical cancer include early onset of sexual activity and multiple partners, smoking, and a weakened immune system (such as people who are on steroids or immunosuppressive medications). Inadequate cervical cancer screening may also increase the risk by missing the opportunity to detect abnormal cells before they turn cancerous.
What Are the Symptoms of Cervical Cancer?
Early cervical cancer and precancerous changes usually cause no symptoms, which is why regular screening is so important. Generally symptoms occur when cervical cancer has already developed. These include abnormal vaginal bleeding, including bleeding between periods, after intercourse or after menopause, unusual vaginal discharge or pelvic pain. These symptoms are not specific to cervical cancer but they should always be evaluated by a gynecologist.
Why Cervical Cancer Screening Works
Cervical cancer screening is effective because of two reasons. Firstly, it can detect abnormal cells before cancer develops. Secondly, it identifies HPV infection which may be associated with changes in the cells of the cervix.
Progression from HPV infection to precancerous lesions (cervical intraepithelial neoplasia, or CIN), and eventually to cervical cancer, is a slow process that often takes 10–20 years. This long timeline allows for early detection and timely treatment, significantly reducing the risk of developing cervical cancer.
Pap Smear vs HPV Testing: What’s the Difference?
Pap Smear (Cytology)
Traditionally, the Pap smear has been used to screen for cervical cancer. During a Pap smear, cells are collected from the cervix and examined under a microscope to look for abnormalities, including precancerous and cancerous cells.
Pap smears have played a critical role in reducing cervical cancer rates. However, they have lower sensitivity compared to HPV testing, detecting precancerous changes in approximately 63–73% of cases. This means that some abnormalities may not be identified through Pap testing alone.
HPV Testing
HPV testing detects the presence of high-risk human papillomavirus (HPV) types known to cause cervical cancer.
Unlike a Pap smear, HPV testing does not assess the appearance of the cells. Instead, it identifies the underlying viral infection that can lead to cervical cancer over time. Because HPV infection occurs before cellular changes develop, HPV testing has higher sensitivity than the traditional Pap smear.
However, HPV testing alone does not determine whether abnormal cells are already present.
How These Tests Are Used Today
High-risk HPV testing is currently used as part of co-testing (Pap smear plus HPV testing), as triage for equivocal Pap smear results, or as a primary screening test of its own.
Co-testing provides the highest overall sensitivity, as it evaluates both current cellular changes and the presence of HPV.
Cervical Cancer Screening Guidelines: Thailand and International Practice
Several international guidelines guide cervical cancer screening.
In the United States, most guidelines (USPSTF/ACOG/HRSA) recommend beginning screening at 21 years of age:
– Pap smear every 3 years from 21–29 years of age
– From 30 years of age, primary high-risk HPV testing every 5 years (preferred) OR co-testing (Pap + HPV) every 5 years OR Pap smear every 3 years. Self-collection for HPV testing is now an endorsed option for women 30–65 to improve access (HRSA update 2026).
In Thailand, the Royal Thai College of Obstetricians and Gynaecologists (RTCOG) recommends starting screening at 25 years of age, using one of the following approaches:
– HPV testing or co-testing every 5 years (preferred)
– Pap smear every 2 years
Women under 25 years of age may require earlier screening if they are at higher risk, including those with HIV infection or immunosuppression, multiple partners or a history of sexually transmitted diseases or genital warts.
Your gynecologist can help determine the most appropriate screening strategy based on your individual risk factors.
Self-Collected HPV Testing
For women who prefer not to undergo a pelvic examination, self-collected HPV testing may be an option in selected cases. This method allows patients to collect a vaginal sample themselves, which is then tested for high-risk HPV. It is increasingly endorsed internationally (e.g., HRSA/ACS 2026 updates in the US) and allowed in Thailand per RTCOG guidelines for women who cannot easily access provider-collected testing. While not suitable for everyone, it can improve access to screening for some women.
What Happens If My Result Is Abnormal?
An abnormal screening result does not mean cancer.
If your test result is abnormal, your doctor will review your medical history and screening results. The next step depends on several factors, including your age, your cervical cancer screening history and the type of screening test currently performed.
Depending on your individual risk, your doctor may recommend repeating the test at a shorter interval, additional testing immediately, a colposcopy (a procedure where your doctor takes a closer look at your cervix under magnification, which may include a biopsy). If the initial abnormality identified is severe, your doctor may recommend going straight to treatment.
Cervical cancer screening should be individualized based on a woman’s age, health history, and personal preferences. An OB-GYN can help interpret results, explain options clearly, and guide appropriate next steps using current evidence and clinical guidelines. Regular screening is key so that any abnormality can be detected early and timely treatment provided.
References
1. Royal Thai College of Obstetricians and Gynaecologists. การตรวจคัดกรองมะเร็งทางนรีเวช Gynecologic cancer screening: แนวทางเวชปฏิบัติของราชวิทยาลัยสูตินรีแพทยแห่งประเทศไทย RTCOG Clinical Practice Guideline. Bangkok: Royal Thai College of Obstetricians and Gynaecologists; 2025. Document GY 68-038. Available from: https://www.rtcog.or.th/files/1755740456_721f4208ebed34da63d8.pdf.
2. U.S. Preventive Services Task Force. Screening for cervical cancer: U.S. Preventive Services Task Force recommendation statement. JAMA. 2018;320(7):674-86. doi:10.1001/jama.2018.10897. Available from: https://www.uspreventiveservicestaskforce.org/uspstf/recommendation/cervical-cancer-screening.
3. American College of Obstetricians and Gynecologists. Cervical cancer screening [infographic]. Washington, DC: American College of Obstetricians and Gynecologists; 2021. Available from: https://www.acog.org/womens-health/infographics/cervical-cancer-screening.
Maternal–Fetal Medicine Specialist in Bangkok
Dr. Narisra Srikureja Firer (Dr. Niti)
Dr. Niti is a Bangkok-based OBGYN with subspecialty training in Maternal–Fetal Medicine (MFM). She provides comprehensive care for women across all stages of life, including pregnancy care, deliveries, and general gynecological conditions.
She dedicates her time to private practice at Ruamjairak Hospital and Mission Hospital, and serves as a Maternal–Fetal Medicine Consultant at a large government tertiary care center.
To read Dr. Niti’s full bio, click here.
