BACKGROUND, Routine quality control rescreening often is used to calculate
the false-negative rate (FNR) of gynecologic cytology. Theoretic analysis s
uggests that this is not appropriate, due to the high FNR of rescreening an
d the inability to actually measure it. The authors sought to determine the
FNR of manual rescreening in a large, prospective, two-arm clinical trial
using an analytic instrument in the evaluation.
METHODS. The results of the Autopap System Clinical Trial, encompassing 25,
124 analyzed slides, were reviewed. The false-negative and false-positive r
ates at various thresholds were determined for routine primary screening, r
outine rescreening, Autopap primary screening, and Autopap rescreening by u
sing a simple, standard methodology.
RESULTS. The FNR of routine manual rescreening at the level of atypical squ
amous cells of undetermined significance (ASCUS) was 73%, more than 3 times
the FNR of primary screening; 11 cases were detected. The FNR of Autopap r
escreening was 34%; 80 cases were detected. Routine manual rescreening decr
eased the laboratory FNR by less than 1%; Autopap rescreening reduced the o
verall laboratory FNR by 5.7%. At the same time, the false-positive rate fo
r Autopap screening was significantly less than that of routine manual scre
ening at the ASCUS level (4.7% vs. 5.6%; P < 0.0001). Rescreening with the
Autopap system remained more sensitive than manual rescreening at the low g
rade squamous intraepithelial lesions threshold (FNR of 58.8% vs. 100%, res
pectively), although the number of cases rescreened was low.
CONCLUSIONS. Routine manual rescreening cannot be used to calculate the FNR
of primary screening. Routine rescreening is an extremely ineffective meth
od to detect error and thereby decrease a laboratory's FNR. The Autopap sys
tem is a much more effective way of detecting errors within a laboratory an
d reduces the laboratory's FNR by greater than 25%. Cancer (Cancer Cytopath
ol) 2001;93:106-110. (C) 2001 American Cancer Society.