Ideally, determining the sensitivity and specificity of a screening test would involve a study that applies a “gold standard” test (such as colposcopy with appropriate biopsy) to all participants (whether the screening test is positive or negative). Sensitivity (the percentage of “true-positive” cases that are detected by the screening test) and specificity (the percentage of "true-negative" cases that are negative by the screening test) could be calculated. Such studies have rarely been done for any screening test for cervical cancer. Studies that compare the Papanicolaou (Pap) test with repeat Pap testing have found that the sensitivity of any abnormality on a single test for detecting high-grade lesions is 55% to 80%.[1,2] Because of the usual slow-growing nature of cervical cancer, the sensitivity of a program of regular Pap testing is likely higher.

To determine the sensitivity and specificity of the Pap smear, both a test threshold (i.e., the point at which the test will be considered to be “positive”) and a reference-standard threshold (i.e., the point at which the reference standard is considered to be “positive”) must be defined. In practice, atypical squamous cells of undetermined significance is often used as the test threshold and cervical intraepithelial neoplasia (CIN) 1 is often used as the reference threshold. This combination gives a sensitivity of about 68% and a specificity of about 75%. A more appropriate test threshold may be low-grade squamous intraepithelial lesions, with a reference threshold of CIN 2–3. This combination gives a sensitivity of 70% to 80%, with a specificity of about 95%.[3]

One important factor in the accuracy of the Pap test is the adequacy of the specimen obtained. Adequate training and using such techniques as the cytobrush may improve sensitivity.[4]

References

1. Soost HJ, Lange HJ, Lehmacher W, et al.: The validation of cervical cytology. Sensitivity, specificity and predictive values. Acta Cytol 35 (1): 8-14, 1991 Jan-Feb.  [PUBMED Abstract]
   
   
2. Benoit AG, Krepart GV, Lotocki RJ: Results of prior cytologic screening in patients with a diagnosis of Stage I carcinoma of the cervix. Am J Obstet Gynecol 148 (5): 690-4, 1984.  [PUBMED Abstract]
   
   
3. Nanda K, McCrory DC, Myers ER, et al.: Accuracy of the Papanicolaou test in screening for and follow-up of cervical cytologic abnormalities: a systematic review. Ann Intern Med 132 (10): 810-9, 2000.  [PUBMED Abstract]
   
   
4. Martin-Hirsch P, Lilford R, Jarvis G, et al.: Efficacy of cervical-smear collection devices: a systematic review and meta-analysis. Lancet 354 (9192): 1763-70, 1999.  [PUBMED Abstract]
   
   

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