Pap test

Pap test
Intervention
ICD-9-CM 795.00
MeSH D014626
MedlinePlus 003911

The Papanicolaou test (abbreviated as Pap test, known earlier as Pap smear, cervical smear, or smear test) is a method of cervical screening used to detect potentially pre-cancerous and cancerous processes in the endocervical canal (transformation zone) of the female reproductive system. Unusual findings are often followed up by more sensitive diagnostic procedures, and, if warranted, interventions that aim to prevent progression to cervical cancer. The test was invented by and named after the prominent Greek doctor Georgios Papanikolaou.

A Pap smear is performed by opening the vaginal canal with a speculum, then collecting cells from the outer opening of the cervix of the uterus and the endocervix. The cells are examined under a microscope to look for abnormalities. The test aims to detect potentially pre-cancerous changes (called cervical intraepithelial neoplasia (CIN) or cervical dysplasia), which are caused by sexually transmitted human papillomaviruses. The test remains an effective, widely used method for early detection of pre-cancer and cervical cancer. The test may also detect infections and abnormalities in the endocervix and endometrium. It remains the most common method of cervical screening in the United States, although the UK screening programmes changed their screening method to liquid-based cytology in 2008.[1]

In the United States Pap smear screening is recommended starting around 21 years of age until the age of 65.[2] Guidelines on frequency vary from every three to five years.[2][3][4] If results are abnormal, and depending on the nature of the abnormality, the test may need to be repeated in six to twelve months.[5] If the abnormality requires closer scrutiny, the person may be referred for detailed inspection of the cervix by colposcopy. The person may also be referred for HPV DNA testing, which can serve as an adjunct to Pap testing. Additional biomarkers which may be applied as ancillary test with Pap test are evolving.[6]

Types of screening

For other cervical screening tests and Human Papillomavirus testing, see Cervical screening.

Pap Tests commonly look for epithelial abnormalities/ metaplasia/ dysplasia/ borderline changes, all of which may be indicative of CIN. Nuclei will stain dark blue, squamous cells will stain green and keratinised cells will stain pink/ orange. Koilocytes may be observed where there is some dyskaryosis (of epithelium). The nucleus in koilocytes is typically irregular, indicating possible cause for concern; requiring further confirmatory screens and tests.

In addition, Human Papilloma Virus (HPV) test may be performed either as indicated for abnormal Pap results, or in some cases dual testing is done, where both a Pap smear and HPV test are done.

Indications

Summary of Pap test indications
person's characteristic indication rationale
never had sexual contact no test HPV usually transmitted by sexual contact[7]
under age 21, regardless of sexual history no test more harms than benefits[8][9]
age 20–25 until age 50–60 test every 3–5 years if results normal broad recommendation[7][10]
over age 65; history of normal tests no further testing recommendation of USPSTF, ACOG, ACS and ASCP;[3][7][11][12]
had total hysterectomy for non-cancer disease – cervix removed no further testing harms of screening after hysterectomy outweigh the benefits[8][9]
had partial hysterectomy – cervix remains continue testing as normal
has received HPV vaccine continue testing as normal vaccine does not cover all cancer-causing types of HPV[10]
history of endometrial cancer discontinue routine testing[13] test no longer effective and likely to give false positive[13]

Screening guidelines vary from country to country. In general, screening starts about the age of 20 or 25 and continues until about the age of 50 or 60.[11] Screening is typically recommended every three to five years, as long as results are normal.[7][10]

People with uteruses should wait a few years after they first have intercourse before they start screening, and should not be screened before age 21. American Congress of Obstetricians and Gynecologists (ACOG) and others recommend starting screening at age 21 (since that is a few years after initial sex for most American women).[3][14] Many other countries wait until age 25 or later to start screening. For instance, some parts of Great Britain start screening at age 25. ACOG's general recommendation is that people with uteruses age 30-65 have an annual well-woman examination, that they not get annual Pap tests, and that they do get Pap tests at three-year intervals.[15]

Most people who contract HPV do so soon after becoming sexually active.[4] It takes an average of a year, but can take up to four years, for a person's immune system to control the initial infection. Screening during this period may show this immune reaction and repair as mild abnormalities, which are usually not associated with cervical cancer, but could cause the person stress and result in further tests and possible treatment. Cervical cancer usually takes time to develop, so delaying the start of screening a few years poses little risk of missing a potentially precancerous lesion. For instance, screening people under age 25 does not decrease cancer rates under age 30.[16]

There is little or no benefit to screening people who have not had sexual contact. For example, United States Preventive Services Task Force (USPSTF) recommends waiting at least three years after first sex.[7] HPV can be transmitted in sex between female-assigned people, so those who have only had sex with other female-assigned people should be screened, although they are at somewhat lower risk for cervical cancer.[17]

Guidelines on frequency of screening vary—typically every three to five years for those who have not had previous abnormal smears.[7][10] Some older recommendations suggested screening as frequently as every one to two years, however there is little evidence to support such frequent screening; annual screening has little benefit but leads to greatly increased cost and many unnecessary procedures and treatments.[3] It has been acknowledged since before 1980 that most people can be screened less often.[18] In some guidelines, frequency depends on age; for instance in Great Britain, screening is recommended every 3 years for women under 50, and every 5 years for those over.

Screening should stop about age 65 unless there is a recent abnormal tests or disease. There is probably no benefit screening people aged 60 or over whose previous tests have been negative.[12] If a person's last three Pap results were normal, she can stop at age 65, according to the USPSTF, ACOG, ACS and ASCP;[3][7] England's NHS says 64. There is no need to continue screening after a complete hysterectomy for benign disease.

Pap smear screening is still recommended for those who have been vaccinated against HPV,[10] since the vaccines do not cover all of the HPV types that can cause cervical cancer. Also, the vaccine does not protect against HPV exposure before vaccination.

Those with a history of endometrial cancer should discontinue routine Pap tests.[13] Further tests are unlikely to detect recurrence of cancer but do bring the risk of giving false positive results, which would lead to unnecessary further testing.[13]

More frequent Pap smears may be needed to follow-up after an abnormal Pap smear, or after treatment for abnormal Pap or biopsy results, or after treatment for cancer.

Procedure

Cervix in relation to upper part of vagina and posterior portion of uterus.

For best results, a Pap test should not occur when a person is menstruating. However, Pap smears can be performed during a person's menstrual period, especially if the physician is using a liquid-based test; if bleeding is extremely heavy, endometrial cells can obscure cervical cells, and it is therefore inadvisable to have a Pap smear if bleeding is excessive.

Obtaining a pap smear should not cause pain,[19] but it can if the person has certain untreated vaginal problems such as cervical stenosis or vaginismus, or if the person performing it is too harsh, or uses the wrong size speculum. Many people experience spotting or mild diarrhea afterward.

Many health care providers are under the false impression that only sterile water, or no lubricant at all, should be used to lubricate the speculum. This may result in unnecessary discomfort. A number of studies have shown that using a small amount of water-based gel lubricant does not interfere with, obscure, or distort the PAP smear. Further, cytology is not affected nor some STD testing.[20]

The health care worker begins by inserting a speculum into the person's vagina, which spreads the vagina open and allows access to the cervix. The health care provider then collects a sample of cells from the outer opening or os of the cervix by scraping it with an Aylesbury spatula. An endocervical brush is rotated in the central opening of the cervix. The cells are placed on a glass slide and taken to the laboratory to be checked for abnormalities.

A plastic-fronded broom is sometimes used in place of the spatula and brush. The broom is not as good a collection device, since it is much less effective at collecting endocervical material than the spatula and brush.[21] The broom is used more frequently with the advent of liquid-based cytology, although either type of collection device may be used with either type of cytology.

The sample is stained using the Papanicolaou technique, in which tinctorial dyes and acids are selectively retained by cells. Unstained cells cannot be seen with a light microscope. Papanicolaou chose stains that highlighted cytoplasmic keratinization, which actually has almost nothing to do with the nuclear features used to make diagnoses now.

In some cases, a computer system may prescreen the slides, indicating those that do not need examination by a person or highlighting areas for special attention. The sample is then usually screened by a specially trained and qualified cytotechnologist using a light microscope. The terminology for who screens the sample varies according to the country; in the UK, the personnel are known as cytoscreeners, biomedical scientists (BMS), advanced practitioners and pathologists. The latter two take responsibility for reporting the abnormal sample which may require further investigation.

Automated analysis

In the last decade, there have been successful attempts to develop automated, computer image analysis systems for screening.[22] Although, on the available evidence automated cervical screening could not be recommended for implementation into a national screening program, a recent NHS Health technology appraisal concluded that the 'general case for automated image analysis ha(d) probably been made'.[23] Automation may improve sensitivity and reduce unsatisfactory specimens.[24] Two systems have been approved by the FDA and function in high-volume reference laboratories, with human oversight.

Results

Micrograph of a Pap test showing a low-grade intraepithelial lesion (LSIL) and benign endocervical mucosa. Pap stain.
Micrograph of a Pap test showing trichomoniasis. Trichomonas organism seen in the upper right. Pap stain.
Micrograph of a Pap test showing changes of herpes simplex virus. Pap stain.

In screening a general or low-risk population, most Pap results are normal.

In the United States, about 2–3 million abnormal Pap smear results are found each year.[25] Most abnormal results are mildly abnormal (ASC-US (typically 2–5% of Pap results) or low-grade squamous intraepithelial lesion (LSIL) (about 2% of results)), indicating HPV infection. Although most low-grade cervical dysplasias spontaneously regress without ever leading to cervical cancer, dysplasia can serve as an indication that increased vigilance is needed.

In a typical scenario, about 0.5% of Pap results are high-grade SIL (HSIL), and less than 0.5% of results indicate cancer; 0.2 to 0.8% of results indicate Atypical Glandular Cells of Undetermined Significance (AGC-NOS).

As liquid based preparations (LBPs) become a common medium for testing, atypical result rates have increased. The median rate for all preparations with low-grade squamous intraepithelial lesions using LBPs was 2.9% compared with a 2003 median rate of 2.1%. Rates for high-grade squamous intraepithelial lesions (median, 0.5%) and atypical squamous cells have changed little.[26]

Abnormal results are reported according to the Bethesda system.[27] They include:

Endocervical and endometrial abnormalities can also be detected, as can a number of infectious processes, including yeast, herpes simplex virus and trichomoniasis. However it is not very sensitive at detecting these infections, so absence of detection on a Pap does not mean absence of the infection.

Effectiveness

The Pap test, when combined with a regular program of screening and appropriate follow-up, can reduce cervical cancer deaths by up to 80%.[10]

Failure of prevention of cancer by the Pap test can occur for many reasons, including not getting regular screening, lack of appropriate follow up of abnormal results, and sampling and interpretation errors.[28] In the US, over half of all invasive cancers occur in female-assigned people that have never had a Pap smear; an additional 10 to 20% of cancers occur in those that have not had a Pap smear in the preceding five years. About one-quarter of US cervical cancers were in people that had an abnormal Pap smear, but did not get appropriate follow-up (person did not return for care, or clinician did not perform recommended tests or treatment).

Adenocarcinoma of the cervix has not been shown to be prevented by Pap tests.[28] In the UK, which has a Pap smear screening program, Adenocarcinoma accounts for about 15% of all cervical cancers[29]

Estimates of the effectiveness of the United Kingdom's call and recall system vary widely, but it may prevent about 700 deaths per year in the UK. A medical practitioner performing 200 tests each year would prevent a death once in 38 years, while seeing 152 people with abnormal results, referring 79 for investigation, obtaining 53 abnormal biopsy results, and seeing 17 persisting abnormalities lasting longer than two years. At least one person during the 38 years would die from cervical cancer despite being screened.[30]

Since the population of the UK is about 61 million, the maximum number of people who could be receiving Pap smears in the UK is around 15 million to 20 million (eliminating the percentage of the population under 20 and over 65). This would indicate that the use of Pap smear screening in the UK saves the life of 1 person for every approximately 20,000 people tested (assuming 15,000,000 are being tested yearly). If only 10,000,000 are actually tested each year, then it would save the life of 1 person for every approximately 15,000 people tested.

Practical aspects

The endocervix may be partially sampled with the device used to obtain the ectocervical sample, but, due to the anatomy of this area, consistent and reliable sampling cannot be guaranteed. As abnormal endocervical cells may be sampled, those examining them are taught to recognize them.

The endometrium is not directly sampled with the device used to sample the ectocervix. Cells may exfoliate onto the cervix and be collected from there, so as with endocervical cells, abnormal cells can be recognised if present but the Pap Test should not be used as a screening tool for endometrial malignancy.

In the United States, a pap test itself costs $20 to $30, but the costs for pap test visits can cost over $1,000, largely because additional tests are added that may or may not be necessary.[31]

In pregnancy

Pap tests can usually be performed during pregnancy up to at least 24 weeks of gestational age.[32] Pap tests during pregnancy have not been associated with increased risk of miscarriage. [32] An inflammatory component is commonly seen on Pap smears from pregnant people,[33] and does not appear to be a risk for subsequent preterm birth.[34]

After childbirth, it is recommended to wait 12 weeks before taking a pap test because inflammation of the cervix caused by the birth interferes with test interpretation.[35]

History

The test was invented by and named after the prominent Greek doctor Georgios Papanikolaou who started his research in 1923. Aurel Babeş of Romania independently made similar discoveries in 1927.[36] However, it should be noted that Babeş method was radically different from Papanicolaou's.[37]

Papanicolaou's name was repeatedly submitted to the Nobel Committee and rejected every time. The Nobel Committee delegated the in-depth investigation of Papanicolaou's merits and demerits to the late Professor Santesson, who was at that time the head of pathology at the Stockholm Cancer Institute (the Radiumhemmet). The investigator discovered Babeş' contributions that had never been cited by Papanicolaou and duly reported this fact to the Committee, which then rejected Papanicolaou's Nobel award.[38]

Experimental techniques

In the developed world, cervical biopsy guided by colposcopy is considered the "gold standard" for diagnosing cervical abnormalities after an abnormal pap smear. The procedure requires a trained colposcopist and can be expensive to perform. However, Pap smears are very sensitive and some negative biopsy results may represent undersampling of the lesion in the biopsy, so negative biopsy with positive cytology requires careful follow up.[39]

Experimental visualization techniques use broad-band light (e.g., direct visualization, speculoscopy, cervicography, visual inspection with acetic acid or with Lugol's, and colposcopy) and electronic detection methods (e.g., Polarprobe and in-vivo Spectroscopy). These techniques are less expensive and can be performed with significantly less training. They do not perform as well as Pap smear screening and colposcopy. At this point, these techniques have not been validated by large-scale trials and are not in general use.

Global studies

There are results from a study in the southern United States showing conditions under which females did or did not receive pap tests, who they were, and what their overall reasonings were:

The most common reason reported by female-assigned people as to why they had not a Pap test was cost (25%), followed by reporting a doctor had not recommended the test (22%). Conclusions: Pap testing was most frequent among African Americans. Subsets, such as people with less education, low income, and no health insurance, however, may not be adequately screened for cervical cancer.
Recent Pap test use was somewhat lower among female-assigned people over 65 (86% for ages 65–69, 83% for ages 70–74, 76% for ages 75–79), among white people (82%) and people of other race/ethnicity (85%), among those with less than a high school education (85%), and among those with lower household incomes (86% for $15,000 annually).[40][41]

There are results from a nationwide study in Taiwan showing conditions under which female personnel do or do not receive Pap tests. The following results were gathered:

57.7% of the female medical personnel had received a Pap test in 2008–2010.
Pap-test rates were highest for pharmacists (58.1%) and nurses (58.0%) and lowest for physicians (48.6%).
Female medical personnel not having received Pap tests were older, had chronic diseases, and so on.[42]

These results further suggest that most middle and upper-class people have access to the Pap test and can choose to have one done annually. On the other hand, poor people, like those in the southern US study, may not always have access to the Pap test.

Gallery

Coccoid bacteria

The finding of coccoid bacteria on a pap test is of no consequence with otherwise normal test findings and no infectious symptoms. However, if there is enough inflammation to obscure the detection of pre-cancerous and cancerous processes, it may indicate treatment with a broad-spectrum antibiotic for streptococci and anaerobic bacteria (such as metronidazole and amoxicillin) before repeating the smear. Alternatively, the test will be repeated at an earlier time than it would otherwise.[43] If there are symptoms of vaginal discharge, bad odor or irritation, the presence of coccoid bacteria also may indicate treatment with antibiotics as per above.[43]

References

Notes
  1. ↑ Liquid Based Cytology (LBC), NHS cervical screening programme (accessed 28/03/2011)
  2. ↑ 2.0 2.1 Moyer, VA; U.S. Preventive Services Task, Force (Jun 19, 2012). "Screening for cervical cancer: U.S. Preventive Services Task Force recommendation statement.". Annals of internal medicine 156 (12): 880–91, W312. doi:10.7326/0003-4819-156-12-201206190-00424. PMID 22711081.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 Saslow, D et al. (2012). "American Cancer Society, American Society for Colposcopy and Cervical Pathology, and American Society for Clinical Pathology Screening Guidelines for the Prevention and Early Detection of Cervical Cancer" (PDF). Journal of Lower Genital Tract Disease 16 (3).
  4. ↑ 4.0 4.1 American Cancer Society. (2010). Detailed Guide: Cervical Cancer. Can cervical cancer be prevented? Retrieved August 8, 2011.
  5. ↑ The American College of Obstetricians and Gynecologists (2009). "ACOG Education Pamphlet AP085 – The Pap Test". Washington, DC. Retrieved June 5, 2010.
  6. ↑ Shidham VB, Mehrotra R, Varsegi G, D'Amore KL, Hunt B, Narayan R. p16 INK4a immunocytochemistry on cell blocks as an adjunct to cervical cytology: Potential reflex testing on specially prepared cell blocks from residual liquid-based cytology specimens. CytoJournal [serial online] 2011 [cited 2011 Apr 17];8:1. Available from: http://www.cytojournal.com/text.asp?2011/8/1/1/76379
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 U.S. Preventive Services Task Force (2003). "Screening for Cervical Cancer: Recommendations and Rationale. AHRQ Publication No. 03-515A.". Rockville, MD.: Agency for Healthcare Research and Quality. Retrieved June 5, 2010.
  8. ↑ 8.0 8.1 U.S. Preventive Services Task Force (March 2012). "Screening for Cervical Cancer: Clinical Summary of USPSTF Recommendation". uspreventiveservicestaskforce.org. Retrieved 31 July 2012.
  9. ↑ 9.0 9.1 American Academy of Family Physicians. "Five Things Physicians and Patients Should Question" (PDF). Choosing Wisely: an initiative of the ABIM Foundation (American Academy of Family Physicians). Retrieved August 14, 2012{{inconsistent citations}}
  10. ↑ 10.0 10.1 10.2 10.3 10.4 10.5 Arbyn M, Anttila A, Jordan J, Ronco G, Schenck U, Segnan N, Wiener H, Herbert A, von Karsa L (2010). "European Guidelines for Quality Assurance in Cervical Cancer Screening. Second Edition—Summary Document". Annals of Oncology 21 (3): 448–458. doi:10.1093/annonc/mdp471. PMC 2826099. PMID 20176693.
  11. ↑ 11.0 11.1 Strander B (2009). "At what age should cervical screening stop?". Brit Med J 338: 1022–23. doi:10.1136/bmj.b809. PMID 19395422.
  12. ↑ 12.0 12.1 Sasieni P, Adams J, Cuzick J (2003). "Benefit of cervical screening at different ages: evidence from the UK audit of screening histories". Br J Cancer 89 (1): 88–93. doi:10.1038/sj.bjc.6600974. PMC 2394236. PMID 12838306.
  13. ↑ 13.0 13.1 13.2 13.3 Society of Gynecologic Oncology (February 2014). "Five Things Physicians and Patients Should Question". Choosing Wisely: an initiative of the ABIM Foundation (Society of Gynecologic Oncology). Retrieved 19 February 2013{{inconsistent citations}}, which cites
    • Salani R, Backes FJ, Fung MF, Holschneider CH, Parker LP, Bristow RE, Goff BA (2011). "Posttreatment surveillance and diagnosis of recurrence in women with gynecologic malignancies: Society of Gynecologic Oncologists recommendations". American Journal of Obstetrics and Gynecology 204 (6): 466–78. doi:10.1016/j.ajog.2011.03.008. PMID 21752752.
    • Salani R, Nagel CI, Drennen E, Bristow RE (2011). "Recurrence patterns and surveillance for patients with early stage endometrial cancer". Gynecologic Oncology 123 (2): 205–7. doi:10.1016/j.ygyno.2011.07.014. PMID 21820709.
    • Bristow RE, Purinton SC, Santillan A, Diaz-Montes TP, Gardner GJ, Giuntoli RL (2006). "Cost-effectiveness of routine vaginal cytology for endometrial cancer surveillance". Gynecologic Oncology 103 (2): 709–13. doi:10.1016/j.ygyno.2006.05.013. PMID 16797686.
  14. ↑ "ACOG Committee on Gynecologic Practice; Routine Pelvic Examination and Cervical Cytology Screening, Opinion #413". Obstetrics and Gynecology 113 (5): 1190–1193. 2009. doi:10.1097/AOG.0b013e3181a6d022. PMID 19384150.
  15. ↑ American Congress of Obstetricians and Gynecologists. "Five Things Physicians and Patients Should Question". Choosing Wisely: an initiative of the ABIM Foundation (American Congress of Obstetricians and Gynecologists). Retrieved August 1, 2013., which cites
  16. ↑ Sasieni, P; Castanon, A; Cuzick, J; Snow, J; (2009). "Effectiveness of Cervical Screening with Age: Population based Case-Control Study of Prospectively Recorded Data". BMJ 339: 2968–2974. doi:10.1136/bmj.b2968.
  17. ↑ Marrazzo JM, Koutsky LA, Kiviat NB, Kuypers JM, Stine K (2001). "Papanicolaou test screening and prevalence of genital human papillomavirus among women who have sex with women". American Journal of Public Health 91 (6): 947–952. doi:10.2105/AJPH.91.6.947. PMC 1446473. PMID 11392939.
  18. ↑ Smith, RA; et al. (2002). "American Cancer Society Guideline for the Early Detection of Cervical Neoplasia and Cancer" 52 (1). pp. 8–22. ACS and others have recommended, since before 1980, that conventional cytology can be safely performed up to every three years for most women.
  19. ↑ "Excerpts from Changing Bodies, Changing Lives". Our Bodies Ourselves. Retrieved 2013-07-02.
  20. ↑ Wright, Jessica L. (2010). "The Effect of Using Water-based Gel Lubricant During a Speculum Exam On Pap Smear Results". School of Physician Assistant Studies. Pacific University. Retrieved 4 February 2012.
  21. ↑ Martin-Hirsch P, Lilford R, Jarvis G, Kitchener HC (1999). "Efficacy of cervical-smear collection devices: a systematic review and meta-analysis". Lancet 354 (9192): 1763–1770. doi:10.1016/S0140-6736(99)02353-3. PMID 10577637.
  22. ↑ Biscotti CV, Dawson AE, Dziura B, Galup L, Darragh T, Rahemtulla A, Wills-Frank L (2005). "Assisted primary screening using the automated ThinPrep Imaging System". Am. J. Clin. Pathol. 123 (2): 281–7. doi:10.1309/AGB1MJ9H5N43MEGX. PMID 15842055.
  23. ↑ Willis BH, Barton P, Pearmain P, Bryan S, Hyde C, "Cervical screening programmes: can automation help? Evidence from systematic reviews, an economic analysis and a simulation modelling exercise applied to the UK". Health Technol Assess 2005 9(13).
  24. ↑ Davey E, d'Assuncao J, Irwig L, Macaskill P, Chan SF, Richards A, Farnsworth A (2007). "Accuracy of reading liquid based cytology slides using the ThinPrep Imager compared with conventional cytology: prospective study". BMJ 335 (7609): 31. doi:10.1136/bmj.39219.645475.55. PMC 1910624. PMID 17604301.
  25. ↑ "Pap Smear". Retrieved 2008-12-27.
  26. ↑ Eversole GM, Moriarty AT, Schwartz MR, Clayton AC, Souers R, Fatheree LA, Chmara BA, Tench WD, Henry MR, Wilbur DC (2010). "Practices of participants in the college of american pathologists interlaboratory comparison program in cervicovaginal cytology, 2006". Archives of pathology & laboratory medicine 134 (3): 331–5. doi:10.1043/1543-2165-134.3.331. PMID 20196659.
  27. ↑ Nayar R, Solomon D. Second edition of 'The Bethesda System for reporting cervical cytology' – Atlas, website, and Bethesda interobserver reproducibility project. CytoJournal [serial online] 2004 [cited 2011 Apr 16];1:4. Available from: http://www.cytojournal.com/text.asp?2004/1/1/4/41272
  28. ↑ 28.0 28.1 DeMay, M. (2007). Practical principles of cytopathology. Revised edition. Chicago, IL: American Society for Clinical Pathology Press. ISBN 978-0-89189-549-7.
  29. ↑ "Cancer Research UK website". Retrieved 2009-01-03.
  30. ↑ Raffle AE, Alden B, Quinn M, Babb PJ, Brett MT (2003). "Outcomes of screening to prevent cancer: analysis of cumulative incidence of cervical abnormality and modelling of cases and deaths prevented". BMJ 326 (7395): 901. doi:10.1136/bmj.326.7395.901. PMC 153831. PMID 12714468.
  31. ↑ Bettigole C (2013). "The Thousand-Dollar Pap Smear". New England Journal of Medicine 369 (16): 1486–1487. doi:10.1056/NEJMp1307295. PMID 24131176.
  32. ↑ 32.0 32.1 PapScreen Victoria > Pregnant women from Cancer Council Victoria 2014
  33. ↑ Michael CW (1999). "The Papanicolaou Smear and the Obstetric Patient: A Simple Test with Great Benefits". Diagnostic Cytopathology 21 (1): 1–3. doi:10.1002/(SICI)1097-0339(199907)21:1<1::AID-DC1>3.0.CO;2-0. PMID 10405797.
  34. ↑ Lanouette JM, Puder KS, Berry SM, Bryant DR, Dombrowski MP (1997). "Is inflammation on Papanicolaou smear a risk factor for preterm delivery?". Fetal diagnosis and therapy 12 (4): 244–247. doi:10.1159/000264477. PMID 9354886.
  35. ↑ "Pregnant women". papscreen.org. Cancer Council Victoria. Retrieved 2015-01-16.
  36. ↑ M.J. O'Dowd, E.E. Philipp, The History of Obstetrics & Gynaecology, London, Parthenon Publishing Group, 1994, p. 547.
  37. ↑ Diamantis A, Magiorkinis E, Androutsos G., What's in a name? Evidence that Papanicolaou, not Babes, deserves credit for the Pap test., Diagn Cytopathol. 2010 Jul;38(7):473-6. doi:10.1002/dc.21226
  38. ↑ Koss, Leopold G. M.D., International Journal of Gynecology Pathology, http://journals.lww.com/intjgynpathology/Fulltext/2003/01000/Aurel_Babes.20.aspx#P20
  39. ↑ Bewtra C, Pathan M, Hashish H. Abnormal Pap smears with negative follow-up biopsies: Improving cytohistologic correlations. http://onlinelibrary.wiley.com/doi/10.1002/dc.10329/abstract
  40. ↑ http://web.ebscohost.com/ehost/pdfviewer/pdfviewer?sid=c456f9bb-cab6-4f69-a99e-d44cf337b135%40sessionmgr111&vid=2&hid=127#944 (see Tables 3 and 4)
  41. ↑ NB Peterson; HJ Murff; Y Cui; M Hargreaves; JH Fowke (Jul–Aug 2008). "Papanicolaou testing among women in the southern United States". Journal of Women's Health 17 (6): 939–46. doi:10.1089/jwh.2007.0576. Retrieved October 15, 2013.
  42. ↑ Fang-Hsin Leea, Chung-Yi Lic, Hsiu-Hung Wanga, Yung-Mei Yang. "The utilization of Pap tests among different female medical personnel: A nationwide study in Taiwan". Preventive Medicine 56 (6). doi:10.1016/j.ypmed.2013.03.001. Retrieved September 20, 2013.
  43. ↑ 43.0 43.1 OB-GYN 101: Introductory Obstetrics & Gynecology > Coccoid Bacteria by Michael Hughey Hughey at Texas Tech University Health Sciences Center. Retrieved Feb 2014.

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