Pap test


The Papanicolaou test, cervical smear, cervical screening, or smear test ) is a method of cervical screening used to detect potentially precancerous and cancerous processes in the cervix or, more rarely, anus. Abnormal 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 independently invented in the 1920s by the Greek physician Georgios Papanikolaou and named after him. A simplified version of the test was introduced by the Canadian obstetrician Anna Marion Hilliard in 1957.
A Pap smear is performed by opening the vagina with a speculum and collecting cells at the outer opening of the cervix at the transformation zone, using an Ayre spatula or a cytobrush. The collected cells are examined under a microscope to look for abnormalities. The test aims to detect potentially precancerous changes or cervical dysplasia; the squamous intraepithelial lesion system caused by human papillomavirus, a sexually transmitted DNA virus. The test remains an effective, widely used method for early detection of precancer and cervical cancer. While the test may also detect infections and abnormalities in the endocervix and endometrium, it is not designed to do so.
Guidelines on when to begin Pap smear screening are varied, but usually begin in adulthood. Guidelines on frequency vary from every three to five years. If results are abnormal, and depending on the nature of the abnormality, the test may need to be repeated in six to twelve months. If the abnormality requires closer scrutiny, the patient may be referred for detailed inspection of the cervix by colposcopy, which magnifies the view of the cervix, vagina and vulva surfaces. The person may also be referred for HPV DNA testing, which can serve as an adjunct to Pap testing. In some countries, viral DNA is checked for first, before checking for abnormal cells. Additional biomarkers that may be applied as ancillary tests with the Pap test are evolving.

Medical uses

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. Screening is typically recommended every three to five years, as long as results are normal.
American Congress of Obstetricians and Gynecologists and others recommend starting screening at age 21. 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 female reproductive organs 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 to five year intervals.
HPV is passed through skin to skin contact; sex does not have to occur, although it is a common way for it to spread. It takes an average of a year, but can take up to four years, for a person's immune system to clear 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 patient 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.
HPV can be transmitted in sex between females, so those who have only had sex with other females should be screened, although they are at somewhat lower risk for cervical cancer.
Guidelines on frequency of screening vary—typically every three to five years for those who have not had previous abnormal smears. 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. It has been acknowledged since before 1980 that most people can be screened less often. In some guidelines, frequency depends on age; for instance in Great Britain, screening is recommended every three years for women under 50, and every five years for those over.
Screening should stop at about age 65 unless there is a history of abnormal test result or disease. There is probably no benefit in screening people aged 60 or over whose previous tests have been negative. If a woman's last three Pap results were normal, she can discontinue testing at age 65, according to the USPSTF, ACOG, ACS, and ASCP; 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 since the vaccines do not cover all 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 after hysterectomy. 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.
More frequent Pap smears may be needed to follow up after an abnormal Pap smear, after treatment for abnormal Pap or biopsy results, or after treatment of cancer.

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%.
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. In the US, over half of all invasive cancers occur in females who have never had a Pap smear; an additional 10 to 20% of cancers occur in those who have not had a Pap smear in the preceding five years. About one-quarter of US cervical cancers were in people who had an abnormal Pap smear but did not get appropriate follow-up.
Adenocarcinoma of the cervix has not been shown to be prevented by Pap smears. In the UK, which has a Pap smear screening program, adenocarcinoma accounts for about 15% of all cervical cancers.
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.
Multiple studies have performed sensitivity and specificity analyses on Pap smears. Sensitivity analysis captures the ability of Pap smears to correctly identify women with cervical cancer. Various studies have revealed the sensitivity of Pap smears to be between 47.19 - 55.5%. Specificity analysis captures the ability of Pap smears to correctly identify women without cervical cancer. Various studies have revealed the specificity of Pap smears to be between 64.79 - 96.8%. While Pap smears may not be entirely accurate, they remain one of the most effective cervical cancer prevention tools. Pap smears may be supplemented with HPV DNA testing.

Results

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. Most abnormal results are mildly abnormal or low-grade squamous intraepithelial lesion ), 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, and less than 0.5% of results indicate cancer; 0.2 to 0.8% of results indicate Atypical Glandular Cells of Undetermined Significance.
As liquid-based preparations 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% in 2006, compared with a 2003 median rate of 2.1%. Rates for high-grade squamous intraepithelial lesions and atypical squamous cells have changed little.
Abnormal results are reported according to the Bethesda system. 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.

Pregnancy

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

In transgender individuals

Transgender men are also typically at risk for HPV due to retention of the uterine cervix in the majority of individuals in this subgroup. As such, professional guidelines recommend that transgender men be screened routinely for cervical cancer using methods such as Pap smear, identical to the recommendations for cisgender women.
However, transgender men have lower rates of cervical cancer screening than cisgender women. Many transgender men report barriers to receiving gender-affirming healthcare, including lack of insurance coverage and stigma/discrimination during clinical encounters, and may encounter provider misconceptions regarding risk in this population for cervical cancer. Pap smears may be presented to patients as non-gendered screening procedures for cancer rather than one specific for examination of the female reproductive organs. Pap smears may trigger gender dysphoria in patients and gender-neutral language can be used when explaining the pathogenesis of cancer due to infection, emphasizing the pervasiveness of HPV infection regardless of gender.
Transgender women who have not had vaginoplasties are not at risk of developing cervical cancer because they do not have cervices. Transgender women who have had vaginoplasties and have a neo-cervix or neo-vagina have a small chance of developing cancer, according to the Canadian Cancer Society. Surgeons typically use penile skin to create the new vagina and cervix, which can contract HPV and lead to penile cancer, although it is considerably rarer than cervical cancer. Because the risk of this kind of cancer is so low, cervical cancer screening is not routinely offered for those with a neo-cervix.