A new thinprep cytologic test of cervical cells and its application

Abstract

In order to improve the quality of routine cervical smears, we investigated the new Thinprep cytologic test (TCT) for cervical cells. In this study, 100 women who were enrolled were randomly divided into two groups. In one group, the TCT for cervical cells was applied (TCT group), and in the other group routine cervical smear was used. In addition, the cells in the TCT group were screened by double sifters, and centrifuged using a separation medium so as to eliminate mucus, inflammatory cells and blood cells. According to the cell distribution and the thickness of the smear, the results were assigned to three groups, including satisfactory smears, less satisfactory smears and unsatisfactory smears. The TCT had a higher satisfactory rate (98%) compared to the routine cervical smear (32%) (P<0.01), indicating the TCT was superior to the routine cervical smear. It is concluded that the TCT is more acceptable. Meanwhile, in comparison to the routine cervical smear, the TCT for cervical cells has 5 advantages which can greatly increase the cytological accuracy.

Keywords

thinprep cytologic test / cervical cells / Papanicolaou smear

Introduction

Cervical cancer is one of the most common malignancies in women worldwide, and its mortality is only lower to that of breast cancer [1-3]. In developing countries, cervical cancer is the most frequent cause of death from cancer among women [4-6]. Because of its harmful impact on the health of women, a simple and economical cervical cytologic test is very important to be established for early detection of cervical cancer [7]. In this study, we investigated a new Thinprep cytologic test (TCT) for cervical cells, and explored the feasibility of TCT in cervical cancer screening compared to the routine cervical smear.

Materials and methods

Materials

100 women enrolled from the out-patients of the Department of Gynecology were randomly and equally divided into two groups. In group 1, the patients were subjected to a TCT of cervical cells, and in group 2 the patients received routine cervical smear. All the specimens were subjected to Papanicolaou staining [8].

Methods

Collection of specimens and preparation of smears

Cervical cells were obtained from the patients’ cervix using a routine cervical scraper. The cervical cells in group 1 were smeared directly, and those in group 2 were diluted in 5 mL preserving solution. Next, the cervical cells which were screened by double sifters were transferred to a separating medium and then they were centrifuged at 2000 r/min for 5 min. The cervical cells which had diagnostic value were allowed to precipitate at the bottom of the test tube. The supernatant was discarded and the sediments were used to make the smear. Thereafter, the smears were fixed with 95% alcohol, stained with pap staining, and observed under a microscope.

Screening of preserving and separating solutions

The preserving and separating solutions were screened by comparing many different reagents.

Diagnostic standard [9] and analytical method

According to the uniformity of the cell distribution and the number of overlapped cells on the smears, the results were assigned to three groups: satisfactory smears, less satisfactory smears, and unsatisfactory smears. If cells were well-distributed and the square of the overlapped cells was less than 5%, they were determined as satisfactory smears; if the square of the overlapped cells was in the range of 5% to 20%, they were “less satisfactory” smears; and, if cells were hyper-dispersed and the square of the overlapped cells was more than 20%, they were considered unsatisfactory smears. We used SPSS statistical software12.0 to analyze the results. χ² test was performed in this study to test the significance of differences between the two groups. P<0.05 was considered statistically significant.

Results

The comparison of the preserving fluid and separating medium

The results are shown in Tables 1 and 2.

It was found that the complex compound had the best preservation effect among all the preserving solutions, and the cells were less destroyed and bacterial proliferation was effectively suppressed. Saccharide had the best separation efficiency among the separating media, and it could maintain the morphology of the cervical cells and get satisfactory separation from impurities in the mucus.

Comparison of the TCT group and the traditional hand-made Papanicolaou smear group

In group 2 (TCT group), satisfactory smears were obtained in 48 cases, with the satisfactory rate being 98%. Cervical cells were well-distributed in the range of 20 mm×20 mm, without overlapped cells, mucus impurities, inflammation cells and blood cells. Further, the cell structure was clear. In group 1 (routine method), satisfactory smears were obtained in 16 cases, with the satisfactory rate being 32%. Cervical cells were not well-distributed with overlapped cells, mucus impurities, inflammation cells and blood cells. The results are listed in Table 3.

Discussion

Cervical cancer is the second most important cancer in women after breast cancer [10]. In many developing countries, cervical cancer remains the most common cancer in women. However, according to previous reports, women who do not receive effective screening are prone to suffer from cervical cancer [11]. If most women can be screened on time and effectively, the mortality rate and the incidence rate of cervical cancer will obviously be decreased [12,13].

Detection using routine cervical smears is simple, accurate and indolent, and is widely applied in cervical cancer screening in China and other countries. However, this method has some inherent defects. The accuracy rates of the examination results are different, at between 67.0%-92.6%. The false negative rate of the cytological test was still high, from 5% to 10%. There were also some false positive results during the examination [14,15]. If uncertain atypical squamous cells (ASC) and uncertain atypical glandular cells (AGC) were included, the false negative rate would be 10%-20%. In the traditional artificial Papanicolaou smears, there are no diagnostic cells, so the false negative rate is 53%-90%, which is due to the following two reasons: (1) The pathological cells are not transferred to the slide totally. As said in a previous report, routine smears have more than 80% of the cells being discarded with the cervical scraper [16]. (2) The smears have poor quality, being so uneven and thick, and also have too much mucus, many inflammatory cells and blood cells. There are nearly 40% smears with poor quality, leading to wrong judgments [16]. The Thinprep technique, developed by Cytyc Corporation of the USA, can solve such problems effectively. However, the equipment and apparatus involved are comparatively expensive [17,18].

TCT overcomes all the above-mentioned disadvantages. Cervical scrapers are directly diluted in cell preservation solution, so the specimens can be totally preserved from the scrapers. Simultaneously, TCT avoids cell over-drying during the routine smear process. In addition, there was a significant difference in the satisfactory rate between the TCT group (98%) and the routine cervical smear group (32%) (P<0.05).

TCT is superior to the traditional hand-made Papanicolaou smear. Compared with the routine cervical smears, the smears made by TCT have many advantages: (1) thin cell layers: all the cells were collected in the range of 20 mm×20 mm on the slide, and the cells were well-distributed; (2) double sifter filtration is done in order to eliminate the mucus, the inflammation cells and blood cells; (3) the rate sediment method is used to separate cervical cells and impurities for the purpose of reducing harm to cervical cells; (4) enrichment of diagnostic cells: compared with the traditional hand-made Papanicolaou smear, TCT can make all the cells from the scrapers be diluted in preservation solution. After centrifugation, cervical cells can be transferred to the slide totally. This can also increase the cell number per unit square of slides, meanwhile increase the diagnostic rate, and decrease the false negative rate as well as the false positive rate caused by the smears’ bad quality. Thus, we can get a more accurate examination result; (5) cheap reagents: the reagents used in TCT are very common and cheap, and can be used for screening of large populations.

To sum up, TCT is much better than the traditional hand-made Papanicolaou smear. TCT provides high quality cell smears for cervical cell screening, thereby improving the detection rate of cervical cancer. TCT only has simple operation procedures and cheap reagents, and can be more easily accepted by patients, so it is suitable as a diagnostic method in routine clinics.

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