Measuring interval cancers in population-based screening using different assays of fecal occult blood testing: The district of Florence experience

The fecal occult blood test (FOBT) has demonstrated its efficacy in reducin g mortality from colorectal cancer (CRC). The guaiac-based FOBT has been cr iticized for its low sensitivity. In this study, two different assays for F OBT (guaiac or an immunochemical test based on reversed passive hemagglutin ation [RPHA]) were tested for comparison within a population-based screenin g program for colorectal cancer in the province of Florence (Italy). The pr oportional incidence method was used to calculate sensitivity for both FOBT s, according to rank of screening (first or repeat), age at entry (two grou ps of 50 to 59 and 60 to 70 years old) and lesion site (colon or rectum). W hen comparing FOBTs, the sensitivity multivariate Poisson regression was us ed to adjust for other variables. The sensitivity after the first 2 years w as 50% (95% confidence interval [CI] 34% to 63%) for the guaiac test versus 82% (95% CI 67% to 92%) for RPHA, At multivariate analysis the risk of dev eloping an interval cancer after a guaiac test is almost 3 times that after RPHA (rate ratio = 2.64; 95% CI 1.3 to 5.4), Our study confirms that RPHA is more sensitive than the guaiac test. The assumption that FOBT screening for CRC has to be based on a guaiac test should be reconsidered, and RPHA s hould be recommended as the standard FOBT for screening purposes. (C) 2001 Wiley-Liss, Inc.