Fecal immunochemical tests have an overall diagnostic accuracy of 95% for the detection of colorectal cancer, according to the results of a meta-analysis just published in the Annals of Internal Medicine.
The tests, which have already begun to replace the fecal occult blood test (FOBT) in national screening programs in the United States, Europe, and Asia, were found to be 79% sensitive and 94% specific for CRC.
"This systematic review and meta-analysis suggests that FITs [fecal immunochemical tests] have high accuracy, high specificity, and moderately high sensitivity for detection of CRC," Dr. Douglas Corley of the Kaiser Permanente division of research in Oakland, Calif., and his associates wrote (Ann. Intern. Med. 2014;160:171-81).
FITs are more sensitive at detecting both CRC and adenomas than the FOBT, they maintained, and are also more practical for people to perform at home, requiring only one or two stool samples and no special dietary or medication restrictions.
Despite a greater potential ease of use for mass screening, reports on the diagnostic performance of FITs have been inconsistent, the investigators explained. They therefore performed the meta-analysis to determine the overall diagnostic accuracy and factors affecting the tests’ performance. Nineteen trials were included that involved more than 113,000 individuals and provided data on eight different FITs available for use in the United States.
In addition to the sensitivities and specificities of FITs, positive and negative likelihood ratios (LR) were calculated to assess the ability of the tests to respectively "rule in" or "rule out" a diagnosis of CRC. The threshold set for a positive LR was a value above 5 and for a negative LR was 0.2. Pooled data from the trials showed a positive LR of 13.10 and a negative LR of 0.23.
Increasing the number of FIT samples did not affect the pooled sensitivities, specificities, positive LRs, or negative LRs of FITs for CRC. There also was no great difference in performance between the FIT brands evaluated in the studies. Dr. Corley and his associates pointed out, however, that head-to-head comparisons were not included in most studies so this finding should be interpreted with caution.
Diagnostic performance was affected by the cutoff values used to define a positive test, which might influence which test health systems decide to use, the researchers said.
"Health systems wishing to optimize use of a quantitative FIT should consider the tradeoff between increasing sensitivity (by lowering the cutoff threshold for a positive test) and the resulting increase in the number of positive results," they wrote. The latter could significantly impact colonoscopy resources if more procedures were indicated by a positive test.
The researchers recommended that health systems also look at individual studies comparing single or repeat testing, as the current data do not provide a definitive answer on the effect of sample number on the performance of FITs.
The National Institute of Diabetes and Digestive and Kidney Diseases and the National Cancer Institute funded the research.
