THE SENSITIVITY & SPECIFICITY OF TRUSCAN VERSUS PAP SMEAR IN SCREENING FOR CERVICAL EPITHELIAL ABNORMALITIES AND CANCER PRECURSORS

Abstract

INTRODUCTION : TruScan uses electrical and optical signals to classify cervical tissue pathology with an expert system to produce a real time diagnosis, allowing the clinician to immediately counsel and manage the patient. This eliminates the waiting time for pap smear result which can be stressful.

METHODS : A prospective study involving 367 women recruited from the general population was conducted. Each patient received a TruScan examination, a conventional Pap smear, colposcopy examination, colpophotographs, videocolposcopy and biopsy of any suspicious lesions. HPV DNA testing was obtained when indicated. Cytology analysis was performed by a centralized independent laboratory. Review colposcopy was performed by an independent expert colposcopist using the digital video recorded during the colposcopy session. Estimation of sensitivity, specificity and predictive values for each screening test were calculated by using standard statistical formulae.

RESULTS : The number of cases with any cervical pathology with human papilloma virus infection or greater was 22 with cytology and 150 with TruScan. This difference was found to be statistically significant (p<0.0001) with McNemar¿s Test.

For cervical epithelial abnormalities, the sensitivity for Pap smear was very low (9.1%) but the specificity was high (94.9%). Therefore, not surprisingly, this had resulted in a high false negative (91%) rate and a low false positive rate (5%) for Pap smear. Both, the sensitivity and specificity values for TruScan were quite balanced, being 55% and 62.5 % respectively. The false positive rate for TruScan was 37.5% while the false negative rate was 44.8%. In other words, while Pap smear is good at screening out individuals without the disease, this is done at the expense of a high false negative rate, i.e. those who had the disease were missed.

From the clinicians and patients prespective, screening tests should correctly identify all patients with the disease, and similarly correctly identify all patients who are disease free. In detection of clinically significant high grade lesions (CIN 2/3), the Pap smear scored with a sensitivity of 100% and specificity of 99.7%. The estimated positive and negative predictive values were 83.7% and 100% respectively. In contrast, the TruScan sensitivity is 50% and specificity is 58% respectively. The estimated positive and negative predictive values were 1.3% and 99% respectively.

CONCLUSION : In this study of a general population, TruScan failed to detect as many cases of clinically important high-grade lesions (CIN 2/3) as Pap smear. It does not fulfill the clinical requirements of a true screening test.