Diagnostic Accuracy of a Qualitative Fecal Immunochemical Test Varies With Location of Neoplasia But Not Number of Specimens
Background & Aims: We compared the accuracy of a qualitative fecal immunochemical test (FIT) in identifying patients with proximal vs distal advanced neoplasia and evaluated whether analysis of 2 specimens performed better than analysis of 1 specimen. Distal advanced neoplasia was defined as colorectal cancer (CRC), any colorectal adenoma ≥10 mm in diameter, high-grade dysplasia, or a lesion with villous or tubulovillous histologic characteristics in a location distal to the splenic flexure, including the descending colon, the rectosigmoid, and the rectum. Methods: We collected data from 5343 subjects (50-70 years old) who received 2 FITs (Hemosure; cutoff value, 10 μg hemoglobin/g feces) before colonoscopy in an invitational CRC screening program in Hong Kong from 2008 through 2012. We calculated the FIT's sensitivity, specificity, positive predictive value (PPV), and negative predictive value in detecting colorectal neoplasia. Results: Of the participants, 13.6%, 12.2%, and 6.0% had distal, proximal, and synchronous distal or proximal neoplasia, respectively. Advanced neoplasia was detected in 291 subjects (5.4%); 22 (0.4%) had CRC. FIT detected distal advanced adenoma with 39.7% sensitivity (95% confidence interval [CI], 32.0%-48.0%) vs proximal advanced adenoma with 25.0% sensitivity (95% CI, 17.3%-34.6%; P = .014), distal advanced neoplasia with 40.0% sensitivity (95% CI, 32.5%-47.9%) vs proximal advanced neoplasia with 27.9% sensitivity (95% CI, 20.0%-37.4%; P = .039), and any distal adenoma ≥10 mm, irrespective of other lesion characteristics, with 39.5% sensitivity (95% CI, 31.0%-48.7%) vs proximal adenoma with 25.3% sensitivity (95% CI, 16.5%-36.6%; P = .038). The specificity of FIT in detecting CRC was similar between the proximal and distal colon. FIT detected distal lesions with higher PPV than proximal lesions. One FIT detected advanced neoplasia with 31.8% sensitivity (95% CI, 25.9%-38.4%) and 92.4% specificity (95% CI, 91.6%-93.2%), whereas 2 FITs detected advanced neoplasia with 34.1% sensitivity (95% CI, 28.0%-40.8%; P = .617) and 91.9% specificity (95% CI, 91.0%-92.7%; P = .327). FIT detected distal advanced neoplasia with greater sensitivity and higher PPV than proximal advanced neoplasia. Conclusions: In an analysis of data from subjects who underwent CRC screening in Hong Kong, FIT detected distal advanced neoplasia with higher sensitivity than proximal advanced neoplasia. Analysis of 1 vs 2 specimens by FIT identified advanced neoplasia with similar test characteristics. © 2015 AGA Institute.