Cervical examination is the process of detecting and removing abnormal tissue or cells in the cervix before cervical cancer develops. By aiming to detect and treat cervical neoplasia early, cervical screening aims at the secondary prevention of cervical cancer. Some screening methods for cervical cancer are the Pap test (also known as conventional Pap smear or cytology), fluid-based cytology, HPV DNA testing and visual inspection with acetic acid. Pap test and fluid-based cytology have been effective in reducing the incidence and mortality rate of cervical cancer in developed countries but not in developing countries. Prospective screening methods that can be used in low resource areas in developing countries are HPV DNA testing and visual inspection.
Video Cervical screening
Recommendations
Different countries have different cervical screening recommendations.
In Europe, most countries suggest or offer screening between the ages of 25 and 64. According to the 2010 European guidelines for cervical cancer screening, the age at which to start screening ranges from 20-30 years, "but is privileged before the age of 25 or 30," depending on burden of disease in the population and available resources. In the UK, NHS cervical screening programs are available for women aged 25 to 64; women aged 25 to 49 receive an invitation every 3 years and women aged 50 to 64 receive an invitation every 5 years.
In the United States, screening is recommended for women between the ages of 21-65, regardless of age at the time of sexual initiation or other high-risk behaviors. For healthy women aged 21-29 who have never had an abnormal Pap smear, screening for cervical cancer with cervical cytology (Pap smear) should occur every 3 years, regardless of HPV vaccination status. The preferred screening for women aged 30-65 is "co-testing", which includes a combination of cervical cytology screening and HPV testing, every 5 years. However, it is acceptable to screen this age group with Pap smears every 3 years. In women over age 65, screening for cervical cancer may be discontinued without abnormal screening results in the previous 10 years and no history of high-grade lesions.
In Australia, screening is offered to women aged 18-70, every two years. It's with Pap smears, and apart from sexual history. In Canada, where screening programs are set up at the provincial level, the general recommendation is not to start routine screening until age 25 in the absence of a specific reason, then filter every three years until the age of 69 years. But, for example, in Ontario "The Ontario Cervical Screening Program recommends that sexually active women have Pap tests every 3 years starting at 21 years of age."
In low-resource countries, cervical screening decisions are made on the basis of available resources and it is often not possible to offer cervical screening as often as possible. The greatest impact on reducing cervical cancer appears to result from screening of women aged 30 to 39, so that resources can be directed to that age group.
Maps Cervical screening
Check type
There are several types of inspection methods available. In the United States, cervical screening is usually done using Pap tests (or 'smear tests'), although the UK screening program changed the screening method to liquid-based cytology in 2008.
Conventional cytology
In conventional Pap smears, doctors collect their cells greasing them on a microscope slide and apply fixative. In general, slides are sent to the laboratory for evaluation.
Study the accuracy of conventional cytological reports:
- 72% sensitivity
- 94% specificity
Liquid-based monolayer cytology
Since the mid-1990s, a technique based on placing a sample into a bottle containing liquid media that retains cells is increasingly being used. Two of them are Sure-Path (TriPath Imaging) and Thin-Prep (Cytyc Corp). The media is primarily ethanol based for Sure-Path and methanol for ThinPrep. Once inserted into the bottle, the sample is processed in the laboratory into thin, thin cells, stained, and examined under a light microscope. Fluid samples have the advantage of being suitable for high-risk HPV testing and can reduce unsatisfactory specimens from 4.1% to 2.6%. Proper sampling is very important for the accuracy of the test, because cells that are not in the sample can not be evaluated.
Study the accuracy of liquid-based monolayer cytology reports:
- sensitivity of 61% to 66%, (although some studies have reported an increase in the sensitivity of fluid-based stains)
- Specificity 82% to 91%
Testing human papillomavirus
Human papillomavirus (HPV) infection is the cause of almost all cases of cervical cancer. Most women will succeed in clearing HPV infection within 18 months. Those who have prolonged infection with high-risk types (eg types 16, 18, 31, 45) are more likely to develop Cervical Intraepithelial Neoplasia, because of the effect that HPV has on DNA.
The UK National Health Service now includes "HPV triage" in its screening program. This means that if the initial screening test shows a low-grade outline or abnormal cell result, further tests for HPV are performed on the sample. If this shows HPV present, the patient is called for further examination, but if there is no HPV, the patient continues the regular screening schedule as if no abnormality was found.
Study accuracy of HPV testing reports:
- 88% to 91% sensitivity (to detect CIN 3 or higher) to 97% (to detect CIN2)
- specificity 73% to 79% (to detect CIN 3 or higher) to 93% (to detect CIN2)
By adding more sensitive HPV tests, the specificity may decrease. If the specificity does not decrease, the result is an increase in the number of false-positive tests and, for many women without disease, increased risk of colposcopy, invasive procedures and unnecessary treatment. A useful screening test requires a balance between sensitivity and specificity to ensure that those with the disease are identified appropriately as the person who has it and those who have no unidentified disease have it.
Regarding the role of HPV testing, randomized controlled trials have compared HPV with colposcopy. HPV testing appears sensitive such as colposcopy immediately while reducing the amount of colposkopia required. randomized controlled trials have suggested that HPV testing may follow abnormal cytology or may precede cervical cytologic examination.
A study published in 2007 showed that the act of doing Pap smears results in an inflammatory cytokine response, which can initiate HPV immunology, thereby reducing the risk of cervical cancer. Women who even had a single Pap smear in their history had a lower incidence of cancer. "A statistically significant decrease in positive HPV levels correlated with the number of lifelong pap smears received."
HPV testing may reduce the incidence of grade 2 or 3 Cervical Intraepithelial Neoplasia or cervical cancer detected by subsequent screening tests in women aged 32-38 years according to randomized controlled trials. The relative risk reduction was 41.3%. For patients at the same risk as those in this study (63.0% had CIN 2-3 or cancer), this led to an absolute risk reduction of 26%. 3.8 patients should be treated for one benefit (amount needed to treat = 3.8). Click here to adjust this result to patients at risk of CIN 2-3 higher or lower. One promising prospect in HPV testing is the possibility of self-sampling. HPV testing on its own sample can now be suggested as an additional strategy to reach women who do not participate in routine and future screening programs as a possible screening strategy.
Filtering process
Procedures for testing women who use Pap smears, fluid-based cytology, or HPV testing are similar. Cell samples are collected from the cervix using a spatula or small brush. The cells are then examined for any abnormalities.
To take a cell sample, the health care doctor inserts an instrument, called the speculum, inside the vagina. The speculum has two arms that spread to the vaginal wall to see the cervix. Then, they erode the surface of the cervix with a spatula or a small brush. It collects cell samples from the outer layer of the cervix.
With a Pap smear, cells are collected using a spatula smeared onto the slide for examination under a microscope. In liquid-based cytology, cell samples are drawn using a small brush. The cells are inserted into a fluid container, and analyzed for abnormalities. Cervical cells tested for HPV are collected in the same way.
Removing abnormal cells
Women may be told that they have CIN (cervical intraepithelial neoplasia), or CIS (carcinoma in situ) - these terms describe the various levels of abnormalities found in cervical cells. Abnormal cells can be removed or destroyed using one of several different procedures.
Laser ablation and cryotherapy only treat the cervix that contains abnormal cells. Laser ablation uses lasers to burn abnormal cells, while cryotherapy uses cold probes to freeze cells. These procedures allow normal cells to grow back in place. The loop electrical discharge procedure (called LLETZ or 'large loop excision of the transformation zone' in the UK), cervical conization (or conical biopsy) and hysterectomy lift all areas containing cells that can become pre-cancerous or develop into cervical cancer.
Testing in resource-poor areas
Many resource-poor regions can not provide routine checks, and must rely on rare screening. A study of cervical cancer screening of 131,746 women in rural India found that a single DNA test reduces the number of advanced cervical cancers and deaths over 8 years, while single acetate examination or single Pap smear screening is not. However, a valuable US $ 30-40 DNA test, which is unreachable in many areas, is time consuming, and requires a sophisticated laboratory infrastructure. Simple, affordable, and accurate tests are being evaluated in China and other countries. The new test can be available in the market in 2010 at a much lower cost than the current test.
With HPV testing, there was a 50 percent reduction in the number of deaths from cervical cancer compared to women who were not screened. Compared with other methods, the study showed that HPV testing reported false negatives at least.
More options
The Bill and Melinda Gates Foundation has funded an eight-year study of DNA testing for a virus that causes cervical cancer. The tests produced by Qiagen for a low cost per test with results available in just a few hours allow for a reduction in the annual use of Pap smears. Tests have been shown to work "quite well" in women who take their own swabs rather than allowing doctors to test. This may increase the likelihood of early diagnosis for women who do not want to be screened for discomfort or decency.
Visual inspection to detect pre-cancer or cancer
In areas where Pap smear is not available or affordable, other testing methods have been evaluated.
Visual inspection of the cervix, using acetic acid (white vinegar VIA) or Lugol's iodine (VILI) to highlight precancerous lesions so they can be seen with the "naked eye", shifts precancer identification from the laboratory to the clinic. Such procedures eliminate the need for laboratory and dispatch of specimens, require very little equipment and provide direct test results to women. Various medical professionals - doctors, nurses, or professional midwives - can effectively perform the procedure, provided they receive adequate training and supervision. As a screening test, VIA may perform as well as or better than cervical cytology to accurately identify pre-cancerous lesions. This has been shown in numerous studies in which trained physicians and midlevel providers were correctly identified between 45% and 79% of women at high risk for cervical cancer. For comparison, cytological sensitivity has been shown to be between 47 and 62%. Cytology gives higher specificity (fewer false positives) than VIA. Like cytology, one of the limitations of VIA is that results largely depend on the accuracy of individual interpretations. This means that initial training and ongoing quality control are very important. A false-positive increase is crucial in screen-and-treat settings, as over-treatment and resulting fertility decline are more likely.
VIA can offer significant advantages over Pap in low resource settings, especially in terms of increased screening coverage, improved follow-up care and overall program quality. Due to the need for fewer specialized personnel and less infrastructure, training, and equipment, VIA's public health system can offer cervical cancer screening in more remote (and less than comprehensive) health care settings and achieve higher coverage. Furthermore, the provider may distribute VIA results with the patient immediately, making it possible to screen and treat women during the same visit. This helps ensure that follow-up care can be provided on-site and reduces the number of women who may lose care because they can not return to the clinic at a later time. In a Peruvian "screen and treat" project, for example, only 9% of positive-screened women failed to receive treatment in a single-visit approach, compared with 44% of women lost on treatment using a multi-visit model..
VIA has been successfully paired with cryotherapy, a relatively simple and inexpensive method to treat cervical lesions that can be done by primary care physicians and mid-level providers.
Visual inspection with acetic acid
Also an approach that promises visual inspection with acetic acid (VIA) should be analyzed when considered for public health initiatives. VIA has been shown to have several studies of low specificity compared with cytology and high false positive rates. Entities such as inflammation, cervical condyloma and leukoplakia can give false-positive results from VIA tests. It also has a low positive predictive value that results in overdiagnosis and overtreatment. VIA has severe limitations with lesions over the endocervical canal that can not be visualized; this is a particular major problem for postmenopausal women where the endocervical junction subsides. There are no permanent records of the tests to review later. Between the high-variability community centers have been observed, and even in the Nigerian 2013 study VIA can not be reproduced or sensitive; this led to breaking the spirit of the method in the country.
See also
- CervicalCheck
References
Source of the article : Wikipedia
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