The diagnostic accuracy of two methods for E6&7 mRNA detection in women with minor cytological abnormalities

Objective: To examine the diagnostic accuracy of nucleic acid sequence based amplification (NASBA) and flow cytometry for E6&7 human papillomavirus (HPV) mRNA detection in the triage of minor cytological abnormalities.

Design: Prospective diagnostic accuracy study.

Setting: Gynecology outpatient clinics of a university hospital.

Population: 472 women with low-grade squamous intraepithelial lesion (LSIL) or atypical squamous cells of undetermined significance (ASCUS).

Methods: Residual material of the liquid-based smears was tested by NASBA and by flow cytometry for E6&E7 mRNA expression. Histological diagnosis was used as reference standard.

Main outcome measures: Accuracy indices of the two techniques and of type 16-specific NASBA for the detection of cervical intraepithelial neoplasia (CIN) 2+ and CIN3+, accuracy indices at age >35 years, correlation between NASBA and flow, comparison between integrated and episomal high-risk HPV infection for risk of CIN2+.

Results: Both tests showed increased positivity rates with increasing severity of the lesion (p < 0.05, chi-squared test for trend). There was a positive correlation between NASBA and flow results (phi coefficient = 0.325). NASBA-positive cases were more likely to have CIN2+ than were NASBA-negative/DNA-positive for types 16, 18, 31, 33, 45 (25/73 vs. 4/52, p= 0.0004; Fisher's exact test). In the LSIL group the NASBA accuracy indices for CIN3+ were: sensitivity 75%, specificity 78.7% and positivity rate 20.8%, and for flow 77.8%, 64.5% and 35.9%, respectively.

Conclusions: NASBA has favorable specificity and positivity rates for triaging LSIL prior to colposcopy. A relatively low sensitivity warrants cytological surveillance of the NASBA-negative LSILs. Flow cytometry does not perform as well overall.