Does the increased sensitivity of the new Papanicolaou tests improve the cost-effectiveness of screening for cervical cancer? - Pap

Journal of Family Practice, Feb, 2001 by Carin E. Reust

Myers ER, McCrory DC, Subramanian S, et al. Setting the target for a better cervical screening test: characteristics of a cost-effective test for cervical neoplasia screening. Obstet Gynecol 2000; 96:645-52.

* BACKGROUND The sensitivity of the conventional Pap test is estimated at 51% with a specificity of 98%. Newer technologies including thin-layer cytology (Thin-Prep), computerized re-screening (Papnet), and algorithmic classification (AutoPap) of slides can increase the sensitivity of cervical cancer screening by up to 30% at an increased cost of $5 to $10 per slide. The specificity of the new technologies is not reported. The impact of these tests on cost-effectiveness has not been clearly described.

In general, a screening test is cost-effective (less cost and more benefit) when the incidence of the disease is common enough to warrant screening, the disease has a long asymptomatic period during which the disease can be identified, or the specificity of the test is high, resulting in less false-positive tests. An additional way to improve cost-effectiveness is if the cost of the screening test and subsequent treatments can be decreased through better identification or definitive treatment of clinically progressive disease.

* POPULATION STUDIED This theoretical model used data based on American women aged 15 to 85 years who were at average risk for cervical cancer.

* STUDY DESIGN AND VALIDITY This study is a cost-effectiveness analysis designed to estimate the cost of screening assuming several different scenarios. Cost is defined as direct medical costs, including inpatient and outpatient costs associated with the diagnosis and treatment of cervical dysplasia and cancer. Cost-benefit was estimated using several scenarios including varying the screening interval (1-, 2-, 3-, and 5-year intervals), altering the specificity of the test from 80% to 99% with sensitivity constant at 51%, and altering the sensitivity of the initial screening test from 51% to 99% using a constant specificity of 97%. Costs and years of life were discounted at 3% annually and varied 0% to 5% in sensitivity analysis.

Overall this was a well-done analysis. The authors focused only on direct costs and did not estimate the effect of screening on other costs such as time lost from work and child care expense. Also, the impact of screening on quality of life was not factored into the analysis. Treatment options for atypical squamous cells of uncertain significance, low- through high-grade squamous intraepithelial lesions, and carcinoma are clearly described for determination of costs. Sensitivity analysis included the pertinent variables of sensitivity and specificity of the screening test, and screening intervals. Discount for costs and benefit was included in this analysis

* OUTCOMES MEASURED Effectiveness as measured is the incremental cost per life-year saved.

* RESULTS When a screening Pap test is used at a constant screening interval, increased sensitivity or decreased specificity of the test increases the incremental cost per life-year saved. In this analysis, the diagnosis and treatment of low-grade lesions had the greatest effect on cost-effectiveness estimates. If a new test with increased sensitivity does not cost more than the conventional test, it is only cost-effective if the screening interval is 3 years and the cost of diagnosing and treating low-grade lesions is $550 (which is lower than 75% of the cases in this data). The diagnosis, workup, and treatment of low-grade lesions that may regress contributes to increased cost without benefit. For any screening interval a new screening test with increased sensitivity that costs more than $3 per slide over the conventional test will not be cost-effective.

RECOMMENDATIONS FOR CLINICAL PRACTICE

When considering new screening tests for cervical cancer, increased sensitivity of the test does not guarantee increased cost-effectiveness. Strategies that increase screening in non-screened populations, improve specificity of the initial screening test, or allow longer screening intervals will be necessary for improved cost-effectiveness in this area. Rather than adopting the new Pap tests, the identification and definitive treatment of clinically progressive human papillomavirus infection will be the necessary next step in improving screening for cervical cancer.

Carin E. Reust, MD University of Missouri-Columbia E-mail: reustc@health.missouri.edu