Cytological Techniques

Arbyn et al. [17 (link)] assessed the HPV test positivity rate in women with equivocal or low-grade cervical cytological abnormalities. HPV testing has been proposed as a method to triage women with minor cytological abnormalities identified through screening for cervical cancer using the Pap smear [19 (link), 20 ]. The prevalence of HPV infection reflects the burden of referral and diagnostic work-up when the test is used to triage women with these cytological conditions [17 (link)]. Two groups of minor cytological abnormalties can be distinguished: a) atypical squamous cells of undetermined significance (ASC-US) or borderline dyskaryosis and b) low-grade squamous intraepithelial lesion (LSIL) or mild dyskaryosis. The meta-analysis concluded that the large majority of women with LSIL were infected with HPV suggesting limited utility of HPV triaging. However, for women with ASC-US, more than halve tested negative and could be released from further follow-up. Figure 1 reproduces the meta analysis including 32 studies providing data of HPV infection in case of equivocal cervical cytology (ASC-US). The pooled prevalence of HPV infection, assessed with the Hybrid Capture 2 assay was 43% (95% CI: 39%-46%) (see Figure 1 and Table 2).Figure 1

Meta-analysis of the proportion of women with ASCUS or a borderline Pap smear that have a positive Hybrid Capture II test. Output generated by the Stata procedure metaprop.

The dataset contains author and year which identify each study, where tgroup corresponds with the triage group(ASCUS, LSIL, borderline dyskaryosis). num and denom indicates the number of women with a positive HPV test (HC2 assay) and total number of tested women such that $\mathit{\text{frac}}\left(\frac{\mathit{\text{num}}}{\mathit{\text{denom}}}\right)$ is the proportion with a positive HC2 test. se indicates the standard error computed as $\sqrt{\frac{\mathit{\text{frac}}(1-\mathit{\text{frac}})}{\mathit{\text{denom}}}}$ . lo and up are the lower and upper confidence intervals computed using the ‘exact’ method.

The estrous cycle identification tool was developed using qualitative data from the literature [5] , [9] (link), [10] for the proportion of each cell type in a smear. A graphical representation of the existing data was created to represent the typical changes in cell types that occur during the entire estrous cycle. The continuous changes in cell types (leukocytes, nucleated epithelial, and cornified epithelial) occurring during the estrous cycle result in the lack of clear demarcations between stages and can make it difficult to determine the stage of the estrous cycle. For example, the vaginal cytology of a mouse in estrus is characterized by many cornified epithelia cells. However, if the mouse is in early estrus, nucleated epithelial cells may also be present. Presented here (Figure 1) is an estrous cycle identification tool that shows the changes in cell populations during the entire cycle. The estrous cycle identification tool makes it clear what cells types are present at each point of the cycle, including the transitional phases between each stage.
The estrous cycle identification tool is a visual aid that shows the 4 estrous stages and the relative proportion of cells present in each stage. Each cell type is shown in a different color. The name of each stage of the estrous cycle is shown on the outside of the circle progressing clockwise from one stage to the next. The 4 quadrants are different sizes to represent a rough estimate of how much time is spent in each stage of the estrous cycle.
To use the estrous cycle identification tool, collect cells using the vaginal cytology method described and view them using a compound microscope. Identify the cell types present on the slide and note the relative proportion of each cell type. For example, there may be all leukocytes on the slide or there may be about half cornified epithelial and about half nucleated epithelial cells. Next, look at the estrous cycle identification tool (Figure 1) and place an imaginary arrow on the chart with the end on the center of the chart like a hand on a clock. The arrow is moved clockwise until the cell types and proportion appear under the arrow. Once the arrow is placed, it points to the corresponding stage of estrous.
This tool makes it easy to determine the stage of the cycle when vaginal cytology is used. The relative amount and type of cells present during early proestrus and late metestrus are similar. The nucleated epithelial cells in proestrus are often well-formed, but are often irregularly shaped and vacuolated in metestrus [3] (link). Alternatively, early proestrus and late metestrus can be distinguished using the visual method.

Table 1 presents the number of women that is expected to be screened for cervical cancer in Portugal. This estimation was based on the number of Portuguese women aged between 25 and 60 years and the proportion of women undergoing cervical cytology in Portugal [16 (link)]. No subclass analysis is done regarding age or vaccination and these factors are assumed geographically homogeneous. Thus, 2,199,879 women enter the cohort and are followed during 2 years in the simulation model.Table 1

Number of women enrolled in the cervical cancer screening in Portugal

Geographic region	Women aged 25–60 years old, n =	Cervical cytology (%)	Cohort dimension
Portugal	2,534,423	86.8	2,199,879
Continental Portugal—Norte region	912,749	95.0	867,112
Continental Portugal—Centro region	531,208	89.5	475,431
Continental Portugal—Lisbon region	692,556	81.2	562,355
Continental Portugal—Alentejo region	160,518	75.9	121,833
Continental Portugal—Algarve region	106,498	84.2	89,671
Autonomous region—Azores	63,011	72.5	45,683
Autonomous region—Madeira	67,883	74.4	50,505

References: INE, 2018; Rukhadze et al. [16 (link)]

The main source of uncertainty in the analytical model is associated with the transition probabilities; therefore, a deterministic sensitivity analysis (DSA) was used to investigate the sensitivity of the results of the base case scenario after variations of these input parameters. According to the 2019 “Human Papillomavirus and Related Diseases Report” from the ICO/IARC Information Centre on HPV and Cancer, the prevalence of HPV infection among women with normal cervical cytology in Portugal ranges from 10.5 to 25.4% [24 ]. As such, another DSA was performed to investigate the impact of varying prevalence rates of HPV infection on the results of the study (10.5% and 25.4%). In addition, the unit costs of the diagnostic tests were varied ± 25% (i.e., up and down) to evaluate how they could affect the results. A joint sensitivity analysis was also performed—both the prevalence rates and the costs of the diagnostic tests were varied simultaneously. Finally, the scenarios without discount rate and where the time horizon is 1 year are explored as well.