Stool Testing and Interpretation

Stool testing serves multiple clinical purposes: colorectal cancer screening, infectious disease diagnosis, inflammatory bowel disease assessment, malabsorption evaluation, and pancreatic insufficiency detection. Colorectal cancer screening tests: (1) Guaiac-based fecal occult blood test (gFOBT): detects peroxidase activity of hemoglobin; requires dietary restrictions (avoid red meat, excess vitamin C, NSAIDs 3 days before); largely replaced by FIT. (2) Fecal immunochemical test (FIT): uses antibodies specific to human hemoglobin; no dietary restrictions; detects lower GI bleeding only (hemoglobin degraded in upper GI); preferred over gFOBT — higher sensitivity and specificity for colorectal cancer. (3) Stool DNA test (Cologuard): combines FIT with molecular testing for DNA mutations (KRAS, NDRG4, BMP3) associated with colorectal neoplasia; performed every 3 years; more sensitive but less specific than FIT (more false positives). Infectious stool tests: C. difficile testing uses PCR or toxin EIA (test only formed stool is incorrect — test LIQUID/UNFORMED stools); stool culture for bacterial pathogens (Salmonella, Shigella, Campylobacter, E. coli O157:H7); ova and parasites (O&P) examination for protozoal and helminthic infections. Inflammatory markers: fecal calprotectin (neutrophil-derived protein — elevated in IBD but NOT IBS; distinguishes...