Fecal occult blood testing is inaccurate as part of diagnostic workup

Reference

Lee MW, Pourmorady JS, Laine L. Use of fecal occult blood testing as a diagnostic tool for clinical indications: a systematic review and meta-analysis. Am J Gastroenterol 2020;115(5):662-670.

Synopsis

These authors searched MEDLINE and EMBASE for full publications of any research design, except case reports, that evaluated the use of FOBT, either via guaiac test or fecal immunochemical test (FIT), in the evaluation of adults with clinical indications such as diarrhea, iron deficiency anemia, and so forth. The studies also had to include a reference standard, such as endoscopy. Two authors independently assessed the eligibility of studies for selection, as well as the risk of bias of each included trial. The senior author settled any disagreements. Ultimately, the authors included 22 studies that each enrolled between 26 and 1132 patients. Twelve of the studies evaluated patients with iron deficiency anemia without overt signs of bleeding, 8 included patients with ulcerative colitis, and 2 included patients with diarrhea. Only 2 of the studies were at low risk of bias. Nine studies evaluated guaiac tests and 13 evaluated FITs. Compared with upper or lower endoscopy, FOBT was 58% sensitive (95% CI 53% - 63%) and 84% specific (75% - 89%) for diagnosing any gastrointestinal abnormality in patients with iron deficiency anemia, with no meaningful difference between guaiac or FIT. FOBT was 83% sensitive (72% - 90%) and 79% specific (68% - 86%) for diagnosing colorectal cancer in patients with iron deficiency anemia. In the studies of patients with ulcerative colitis, FOBT (all of the studies used FIT) was 72% sensitive (0.57% - .84%) and 80% specific (67% - 89%) for active disease. For patients with diarrhea, the sensitivities of FOBT (both studies used guaiac testing) were widely divergent (38% and 87%) as were the specificities (85% and 58%).