Is a liquid-based cytology more sensitive than a conventional Pap smear?

The comparative sensitivity of liquid-based cytology (LBC) test and conventional Papanicolaou (Pap) smears is controversial.

This study analyses the distribution of cytology, histology, colposcopy and large loop excision of the transformation zone among women screened in Iceland with LBC at the Cancer Detection Clinic in Reykjavik and with a conventional Pap smear outside the Detection Clinic in 2007-2011. The study material included 42 654 LBC tests from 20 439 women and 103 909 Pap smears from 61 574 women. The period 2000-2004 is used to correct for potential bias as a result of unequal distribution of the studied parameters between the study sites before the introduction of LBC.

The observed results indicated that women screened with an LBC sample had significantly decreased detection rates of inadequate smears, increased detection of low-grade squamous intraepithelial lesion (LSIL)/atypical cytology and referrals to colposcopy, and an increased detection rate of cervical intraepithelial neoplasia grade 2 or worse (CIN2+) irrespective of age. LBC increased significantly the detection rates of high-grade squamous intraepithelial lesion or worse (HSIL+) cytology and CIN3+ histology only in women under 40 years of age. Taking into consideration the unequal prevalence of the studied parameters between the study sites in 2000-2004 indicated, however, that LBC only affected the rate of inadequate and low-grade cytology tests under the age of 40 years. Positive predictive values for CIN2+ were not significantly different between the tests.

The study results support the view that LBC is no more sensitive than Pap smears for the detection of HSIL+ and CIN2+ irrespective of age. LBC decreased the rate of inadequate smears, but increased the rate of low-grade cytology under the age of 40 years and decreased the total rate of abnormal smears over the age of 40 years.