Do liquid-based Pap smears need a transformation zone component?


A many as 20% of specimens from liquid-based cytology may lack a TZ component. The author examines the evidence on whether that should be of concern to clinicians and reveals two easy steps that can help you obtain more TZ in Pap specimens.



Do liquid-based Pap smears need a transformation zone component?

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Choose article section... The University of Washington study Other reports in the literature Putting the results into practice Summing up

By Constance Mao, MD

As many as 20% of specimens from liquid-based cytology may lack a TZ component. The author examines the evidence on whether that should be of concern to clinicians and reveals two easy steps that can help you obtain more TZ in Pap specimens.

More and more clinicians have been using liquid-based cytology for Pap testing since the American Society of Colposcopy and Cervical Pathology (ASCCP) issued guidelines for management of cytologic abnormalities.1 Liquid cytology does improve sensitivity, but many patients and physicians are turning to it for human papillomavirus (HPV) triage testing of Pap tests that show atypical squamous cells of undetermined significance (ASCUS).

Some evidence suggests that a missing transformation zone (TZ) component is more likely when liquid cytology is used for Pap testing than with the traditional technique.2 According to the Bethesda 2001 terminology, TZ component is defined by the presence of at least 10 endocervical or metaplastic cells on a cytology slide.3 This recent report also eliminated the description "satisfactory but limited by" a lack of endocervical cells that clinicians frequently have seen on Pap test reports in recent years. Pap test results now should be described as "satisfactory" if an adequate number of squamous cells is present, and a comment should be included about the presence or absence of TZ component.

Davey recently provided an excellent in-depth review of the ASCCP's Pap smear adequacy guidelines.4 This article reviews the literature concerning lack of TZ component specifically in liquid cytology—including a study by the members of the HPV Research Group at the University of Washington on whether absence of TZ component affects detection of high-grade cervical dysplasia with liquid cytology—and discusses the clinical implications.5

The University of Washington study

The EVA (Evaluation of cervical cancer screening methods) study enrolled 4,389 women at three Western Washington Planned Parenthood clinics, who were screened with liquid cytology and HPV testing. Those who had any abnormal Pap equal to or greater than ASCUS were referred to colposcopy and biopsy and women who were high-risk HPV DNA-positive were referred to colposcopy and biopsy. A subgroup of women with completely negative screening Pap and HPV testing also were offered colposcopy and biopsy.

Overall, 15.9% or 700 liquid cytology smears lacked a TZ component. We found that women aged 30 or older were more likely to have smears without TZ than were those aged 20 or younger. Also, women more than 14 days from their last menstrual period were more likely to have TZ-absent smears. We did find that the frequency of abnormal cytology was higher for women with TZ-positive smears (18.3%) than for women with TZ-negative smears (10.7%) (Table 1). However, for TZ-negative women, repeat Pap smear at the time of colposcopy did not seem to reveal more abnormalities.


EVA study results

Cytology result
TZ present (3,689)
TZ absent (700)
3,010 (81.7%)
624 (89.3%)
673 (18.3%)
75 (10.7%)


382 (10.4%)
56 (8.0%)


168 (4.6%)
14 (2.0%)


123 (3.3%)
5 (0.7%)


The critical clinical question is whether negative smears lacking TZ absent are suboptimal. Are TZ-absent smears more likely to miss a significant lesion? To answer this question we compared women with Pap smears that did and did not have TZ following colposcopy, and we found no difference in the rate of biopsy-proven CIN 2-3 (cervical intraepithelial neoplasia 2-3) in these two groups (Figure 1). Although the rate of CIN 2-3 (6.3%–7.8%) detected following negative Pap smears in this study may seem unusually high, remember that many of our Pap-negative women were HPV DNA-positive and they were referred to colposcopy for that reason. The important point is that we did not find more CIN 2-3 in the Pap smears lacking TZ.



Other reports in the literature

Previous estimates suggest that 10% to 20% of liquid cytology results do not have a TZ component.2,6 Some authors found that liquid cytology was more likely to lack a TZ component than conventional cytology.2 Others found a higher rate of TZ-absent smears in conventional cytology.7 Earlier reports evaluating the clinical significance of a lack of TZ component suggested that these Pap smears were less useful because there was a higher rate of moderate-to-severe abnormalities found on Pap smears that had a TZ component compared to those that did not.8,9 In our study, we also found that TZ-lacking smears were more likely to show cytologic abnormality than TZ-containing smears. This information suggested to some clinicians that TZ-lacking Paps are inferior and should be repeated.

However, a better way to evaluate the difference between Pap smears with and without TZ is to compare histologic results after colposcopy. If colposcopy is performed in a timely fashion, we can evaluate whether negative screening Pap smears that lack a TZ component are more likely to miss significant lesions. In our study, we found no significant difference in the rate of CIN 2-3 in Pap smears with and without TZ.

Previous studies done with conventional Pap smears support our findings. Kivlahan found that women whose Pap smears did (2,542) and did not (3,443) have TZ were not significantly more likely to have atypia on a second screening test.10 Also another study looked at 20,222 women with negative cytology, and no difference was found in subsequent Pap smears whether TZ was present or not.11 Only one longitudinal study compared the detection of CIN 2-3 and cervical cancer following negative Pap smears with and without TZ. Women in the Netherlands were followed for 6.25 to 8.25 years after negative Pap smear and no difference was found in the incidence of CIN 2-3 between those whose Pap smears did and did not have TZ. The rate of invasive cancer was the same for both groups.12

Putting the results into practice

The EVA study was the first to evaluate the clinical implication of TZ-lacking Pap smears for liquid cytology tests. Also, unlike most studies, we restricted our analysis to women with normal screening smears. Because our study was limited to women aged 18 to 50, we cannot comment on older women who may be more likely to have a TZ-lacking Pap. While our study is not adequately powered to detect small differences in the detection of CIN 2-3, our results are supported by previous studies using conventional Pap smears. Since negative Pap smears without TZ did not miss CIN 2-3 more often than those with a TZ component, return to routine screening seems indicated for patients with this result.

In our laboratory experience, there was a temporary rise in both unsatisfactory smears (not enough cells) and Pap smears without TZ component when we switched from conventional to liquid cytology. Although an experienced clinician will have taken many conventional Pap smears, there are some adjustments that need to be made for liquid cytology. For instance, many clinicians remove mucus, discharge, or blood from the cervix with a swab to help prevent obscuring smears on a glass slide. With liquid cytology, however, this practice may remove a significant amount of cellular material, resulting in a scanty sample or a smear that is unsatisfactory because of too few cells.

A second adjustment for clinicians relates to handling the sample. Although there are a number of other collection methods, in our study, we used cytobrush and spatula because it is reported to be best for obtaining TZ component.13 The manufacturer recommends placing the cytobrush and spatula in solution immediately after obtaining the sample, twirling the brush between your fingers, pushing it against the side of the vial, and vigorously swirling it in the solution 10 times. Simple movement of the brush through the liquid, however, sometimes does not remove mucus, and thus the cytobrush may retain many TZ component cells. We suggest that you consider using the spatula to mechanically remove mucus and cells from the cytobrush when necessary. These techniques may help decrease the likelihood of an inadequate smear or one lacking in TZ for a clinician who is making the switch to liquid cytology.

Summing up

The EVA study findings support the clinical recommendations in the new ASCCP guidelines for women with negative Pap smears that show no TZ component. Although liquid cytology may result in more Pap smears lacking TZ, there does not appear to be a difference in the technology's ability to detect CIN 2-3 whether TZ component is present or not. The new ASCCP guidelines recommend a Pap follow-up in 12 months for the woman with a negative Pap smear with no TZ component. A 6-month follow-up may be warranted in some situations, such as previous atypical Pap smears, inability to visualize the cervix, inability to obtain an adequate sample, immunosuppression, or history of insufficient frequency of previous screening. It appears that liquid-cytology Pap smears without a TZ component perform as well as do those with a TZ component.


1. Wright TC Jr, Cox JT, Massad LS, et al. 2001 Consensus Guidelines for the management of women with cervical cytological abnormalities. JAMA. 2002; 287:2120-2129.

2. Roberts JM, Gurley AM, Thurloe JK, et al. Evaluation of the Thin-Prep Pap test as an adjunct to the conventional Pap smear. Med J Aust. 1997;167:466-469.

3. Solomon D, Davey D, Kurman R, et al. The 2001 Bethesda System: terminology for reporting results of cervical cytology. JAMA. 2002;287:2114-2119.

4. Davey DD. Is that Pap specimen adequate? Contemporary OB/GYN. 2002;47(10):34-47.

5. Baer A, Kiviat NB, Kulasingam S, et al. Liquid-based Papanicolaou smears without a transformation zone component: should clinicians worry? Obstet Gynecol. 2002;99:1053-1059.

6. Carpenter AB, Davey DD. ThinPrep Pap test: performance and biopsy follow-up in a university hospital. Cancer. 1999;87:105-112.

7. Weintraub J, Morabia A. Efficacy of a liquid-based thin layer method for cervical cancer screening in a population with a low incidence of cervical cancer. Diagn Cytopathol. 2000;22:52-59.

8. Elias A, Linthorst G, Bekker B, et al. The significance of endocervical cells in the diagnosis of cervical epithelial changes. Acta Cytol. 1983;27:225-229.

9. Mauney M, Eide D, Sotham J. Rates of condyloma and dysplasia in Papanicolaou smears with and without endocervical cells. Diagn Cytopathol. 1990;6:18-21.

10. Kivlahan C, Ingram E. Papanicolaou smears without endocervical cells. Are they inadequate? Acta Cytol. 1986;30:258-260.

11. Mitchell H, Medley G. Longitudinal study of women with negative cervical smears according to endocervical status. Lancet. 1991;337:265-267.

12. Bos AB, van Ballegooijen M, Elske van den Akker-van Marle M, et al. Endocervical status is not predictive of the incidence of cervical cancer in the years after negative smears. Am J Clin Pathol. 2001;115:851-855.

13. Martin-Hirsch P, Lilford R, Jarvis G, et al. Efficacy of cervical-smear collection devices: a systematic review and meta-analysis. Lancet. 1999;354:1763-1770.

Dr. Mao is Acting Assistant Professor, HPV Research Group, Department of Obstetrics and Gynecology, University of Washington, Seattle, Wash.


Constance Mao. Do liquid-based Pap smears need a transformation zone component? Contemporary Ob/Gyn Jul. 1, 2003;48:78-83.

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