The Pap test

The background and evolution of the Pap test

The Pap test, or Papanicolaou test, was developed by the American anatomist, Dr. George Papanicolaou. In 1926, he reported that tumour cells could be seen in the vaginal secretions of women with cervical cancer leading to his publication of the Diagnosis of uterine cancer by the vaginal smear in 1943. The first cervical cancer screening clinic was opened in Massachusetts in 1945 [1].

The Pap test has been used as a screening test worldwide for more than 50 years and has since played a significant role in the dramatic decline of cervical cancer in developed countries. In Canada, screening programs have used the traditional Pap smear test, or in more recent years, liquid-based cytology as the mainstay screening method for cervical cancer [2].

The goal of the Pap test is to screen for precancerous lesions of the cervix and vagina that have the potential to become invasive cancer and reduce the risk of advanced cancer through the detection of asymptomatic or early-stage cancer [3]. The test itself involves scraping a sample of epithelial cells from the surface of the cervix using a spatula, brush or other sampling device.

If the sample is clear, it will be sent to laboratories for testing. Labs in Canada use the Bethesda system to report Pap test results.

These results can be reported as being normal or abnormal. A normal, or negative, result means that there were enough cells in the sample and no cancerous cells were found. Abnormal results in the cervix and vagina are classified based on how deviant they look from normal cells [4]:

  • Normal: There is no evidence of abnormal changes in the cells sampled.
  • ASCUS (Atypical Squamous Cells of Undetermined Significance): The cells are abnormal, but no definite diagnosis can be made. This test result can be caused by a yeast infection, using oral contraceptives, or problems with taking the sample. Usually doctors repeat the Pap smear in a few weeks or test for the presence of high risk types of HPV.
  • LSIL (Low-grade Squamous Intraepithelial Lesion): This result means an acute infection. If it persists for at least two to three visits, it can be assumed that it could lead to cancer.
  • HSIL (High-grade Squamous Intraepithelial Lesion): This result means more advanced lesions.
  • AGC (Atypical Glandular Cells): these abnormal cells are the precursors of about 20 per cent of cervical cancers. These cells are very difficult to detect.

Abnormal results do not mean there is a precancerous condition or cancer present, some may return to normal on their own while others may develop into cancer over time. Every year, almost 400,000 Canadian women have an abnormal Pap test result [5].

If the result of a Pap test is abnormal, together with your doctor you will decide if you need to have follow-up tests, treatment or both—follow-up options another include Pap test or a colposcopy.

Limitations of the Pap test

While the Pap test can be an effective tool for preventing cervical cancer, no screening test is entirely accurate and does have a risk of giving misleading results [6]:

  • the sample may not contain abnormal cells which may still be present on the cervix;
  • some samples are hard to interpret ; for example, blood or mucus may make it hard to see the cells
  • occasionally, abnormal cells are missed under the microscope
  • sometimes abnormal cells occur in cells high up in the cervix or deep in the glands of the cervix (adenocarcinoma); it is not always possible to get samples from these areas

If the results are inaccurate, it is called a false-negative result; this means the test didn’t find cancer or abnormal cells even though they are present. This can occur if the sample doesn’t have enough tissue or if abnormal cells in the sample are missed. Inaccurate results can also be false-positive, which means the test shows abnormal cells when they are not present. A false-positive result may lead to unnecessary follow-up tests, procedures and anxiety for the patient [7].

As the Pap test can miss precancerous changes in the cervix or mistake normal changes for precancerous ones, the Pap test needs to be repeated frequently. In fact, the Canadian Cervical Screening Trial (CCCaST) reported when using the Pap test there was only a detection rate of 55 per cent in cases in which women had precancerous changes to their cervix, compared with the HPV test which detected 95 per cent of precancerous changes [8].

Pap tests must be sampled properly and even then the samples are challenging to interpret. Deficiencies or errors in any one of the analytic steps may explain a false-negative result despite the presence of a dysplastic lesion (pre-cancerous condition) or cervical cancer. One study reported that sampling errors by the clinician accounted for 62 per cent of false-negative smears, while interpretive errors by the pathologist accounted for 22 per cent, and screening errors by the cytotechnician were responsible for 16 per cent [9].


[1] “Evolution of the Pap Smear to Cervical Cancer Screening Today.” Eurocytology. Eurocytology, 2014. Web. 12 Aug. 2015.
[2] Murphy, Joan, Erin B. Kennedy, Sheila Dunn, C. Meg McLachlin, Michael Fung Kee Fung, Danusia Gzik, Michael MD, and Lawrence Paszat. “HPV Testing in Primary Cervical Screening: A Systematic Review and Meta-Analysis.” Journal of Gynaecological Oncology (2012): 443-52. Journal of Gynaecological Oncology. Journal of Gynaecological Oncology, May 2012. Web. 16 Sept. 2015.
[3] ibid.
[4] Maclean, D., A. Ollner, and SR Hosein. “HPV, Cervical Dysplasia and Cancer.” HPV, Cervical Dysplasia and Cancer. CATIE, 2013. Web. 11 Sept. 2015.
[5] “What Is the Difference between Normal and Abnormal Results?” Pap Testing. Society of Obstetricians and Gynaecologists of Canada, 2015. Web. 16 Sept. 2015.
[6] “Limitations of the Pap Test.” PapScreen Victoria. PapScreen Victoria, 2015. Web. 13 Aug. 2015.
[7] “Risks with a Pap Test.” Pap Tests. Canadian Cancer Society, 2015. Web. 13 Aug. 2015.
[8] Picard, André. “HPV Test Tops Pap in Cervical Cancer Detection.” The Globe and Mail. The Globe and Mail, 03 Apr. 2009. Web. 13 Aug. 2015.
[9] McMeekin, D. Scott, MD, Kathryn F. McGonigle, MD, and Steven A. Vasilev, MD. “Cervical Cancer Prevention: Cost-Effective Screening.” Women’s Cancer Information Center. Women’s Cancer Center, 2007. Web. 14 Aug. 2015.

Advances in the Pap smear and cytology

New techniques have been developed to further enhance specimen collection and interpretation of the Pap test. The ThinPrep method and the LUMA Cervical Imaging System have been introduced and approved by the FDA to improve the quality of specimen collection [6]. These technologies optimize cell preservation and reduce mucus, blood or other debris on the slide that gets in the way discovering pre-cancerous or cancerous cells.

In one study of 251 patients using the ThinPrep method, excellent correlation was shown between the standard Pap smear and the ThinPrep [7]. Slides can be read faster, from a smaller sample area, and with fewer numbers of cells needed to make the correct diagnosis.

Cervical cells are usually collected on a small stick or spatula then smeared on a slide for analysis. A 1994 study found that up 80 per cent of the sample taken from a patient using the conventional Pap smear technique did not make its way onto the slide, but rather stayed collection device [8]. Now instead of smearing the cervical cells onto a slide, a new ‘direct-to-vial’ technique is used. This involves immediately rinsing the collected cells into a vial filled with a special solution. This reduces the likelihood that a patient’s cell sample will be damaged by air, clumping, and so on.

The vial is then taken to the laboratory for slide preparation and screening. In the laboratory, the vial is inserted in a sample preparation device which breaks up blood, mucus, and other debris. The thin layer of cells in then transferred to a slide and deposited into a preservative solution. With newer methods, physicians are now able to conduct multiple analyses using residual cells collected in the vial instead of having to order an additional Pap smear. In a clinical trial of 6,747 patients conducted by Cytyc, the maker of the ThinPrep direct-to-vial technique, researchers found a 65 per cent improvement in the detection of cervical cancer at three screening centers using this new technique and a 6 per cent improvement at three hospitals where the incidence of cervical cancer is historically high [9].

The use of computerized instruments to recognize abnormal cells in Pap smears are now also being used. Typically, technologists and clinicians evaluate all Pap smear samples, but with this technology, a computer re-examines the sample and marks areas of the sample that may indicate abnormal cells. The technologist or physician then takes a closer look at these areas. The added advantage is that it may find pre-cancerous or cancerous cells that a technologist or physician might otherwise miss [10]. However, some critics believe that use of these technologies will increase the number of false positive results or ASCUS (atypical cells of undetermined significance) diagnoses [11], which could lead to patient anxiety and unnecessary follow-up examinations.

Certain adjuvant tests have also been introduced to improve sensitivity and specificity of cervical cancer screening. These tests include HPV detection, new techniques for visualizing acetic-acid-stained cervical specimens, and molecular markers. The overall concern for many of these techniques, such as cervicography, speculoscopy, and molecular markers, is maintaining balance between augmenting the effectiveness of the Pap test while keeping it cost-effective [12]. Subsequently, a gap in differentiating between low risk and high risk patients must be filled, so unnecessary surveillance and treatment can be avoided.

Cervical screening in conjunction with the HPV vaccination

In 2007, the federal allocated $300 million over three years to provinces and territories on a per capita basis to support the launch of a national vaccination program against the HPV virus. All the provinces and the Yukon implemented voluntary vaccination programs targeting various groups of females between the ages of 9 and 17. Gardasil, the first Health Canada approved HPV vaccine, protected against the two high-risk cancer-causing types of HPV (16 and 18) and the two low-risk types (6 and 11) which cause anogenital warts [13].

Over three years, the $300 million on a per capita basis was designed to provide the provinces and territories with the opportunity to create and implement an equal opportunity vaccination program for young females. The execution of the vaccination programs varied wildly across the provinces: certain provinces had a program that only covered a younger group of females, while others covered a second age group in later grades [14]. Eligibility for female participation in the voluntary vaccination program also varied across the provinces, with Quebec estimating 100 per cent coverage and, the lowest, Manitoba, citing 32 per cent [15]. As such, the differences in provincial vaccination programs may result in the levels of cervical cancer incidence across the provinces.

The implementation of provincial and territorial vaccination programs decision bears no relationship to the risk of cervical cancer in the respective jurisdictions. For example, Quebec and BC with the lowest incidence rate of cervical cancer at six per 100,000 females, but have two of the best programs capturing 100 and 65 per cent of females aged 9–17 years, respectively. Provinces with the highest incidence rates such as Nova Scotia with 11 and Prince Edward Island with 10 cases per 100,000 females are only capturing 53 and 41 per cent of females in their programs [16].

Based on existing inconsistencies across the provinces, it remains imperative that cervical cancer screening continues to be offered and promoted as a necessary part of the cervical cancer prevention program [17].


[6] “What Are the Latest Advances with Pap Smear?” Imaginis. Imaginis, 21 Nov. 2007. Web. 14 Aug. 2015.
[7] McMeekin, D. Scott, MD, Kathryn F. McGonigle, MD, and Steven A. Vasilev, MD. “Cervical Cancer Prevention: Cost-Effective Screening.” Women’s Cancer Information Center. Women’s Cancer Center, 2007. Web. 14 Aug. 2015.
[8] “What Are the Latest Advances with Pap Smear?” Imaginis. Imaginis, 21 Nov. 2007. Web. 14 Aug. 2015.
[9] ibid.
[10] ibid.
[11] Fayed, Lisa. “ASCUS Pap Smear Results.” ASCUS Pap Smear Results. About Health, 10 Dec. 2014. Web. 14 Aug. 2015.
[12] McMeekin, D. Scott, MD, Kathryn F. McGonigle, MD, and Steven A. Vasilev, MD. “Cervical Cancer Prevention: Cost-Effective Screening.” Women’s Cancer Information Center. Women’s Cancer Center, 2007. Web. 14 Aug. 2015.
[13] Colucci, Rosemary, William Hryniuk, and Colleen Savage. “HPV Vaccination Programs in Canada: ARE WE HITTING THE MARK?” Cancer Advocacy. Cancer Advocacy Coalition, 2008. Web. 14 Aug. 2015.
[14] ibid.
[15] ibid.
[16] ibid.
[17] ibid.