Comparative screening with a sensitive guaiac and specific immunochemical occult blood test in an endoscopic study

HemoccultSENSA (HOS), the sensitive guaiac fecal occult blood test (FOBT) for colorectal neoplasia, is faulted for its low specificity, which might be improved by substituting or adding FlexSure OBT (FS), the immunochemical test for human hemoglobin. (Both tests are manufactured by Beckman-Coulter Inc., Primary Care Diagnostics, Palo Alto, CA.) The authors compared both FOBTs in an endoscopic study to determine which FOBT to recommend for a population-screening program.

Both FOBTs, without dietary restrictions, were prepared by 1410 screenees or nonbleeding symptomatic patients (3%). All underwent colonoscopy (51.8%) or flexible sigmoidoscopy (if asymptomatic and both FOBTs were negative).

HOS sensitivity for significant neoplasia, cancers, or adenomas >/= 1 cm (20 cases) was similar to that of FS (50% vs. 35%, not significant). However, HOS specificity was lower (95% vs. 99%, confidence interval (CIs) 94-96 vs. 98-99, P < 0.05). In those 11 cases in which both HOS and FS were positive, specificity for significant neoplasia was 100% but sensitivity decreased to 25% (less than HOS alone, P < 0.05). HOS was more sensitive than FS for any neoplasia (55 cases), including adenomas < 1 cm (35% vs. 18%, CIs 22-47 vs. 8-28, P < 0.05), but less specific (96% vs. 99%, CIs 95-97 vs. 98-100, P < 0.05).

Guaiac HOS, which does not require dietary restrictions, is significantly more sensitive for any colorectal neoplasm than the immunochemical FS; it identifies more adenomas with a specificity that is low but acceptable for population screening.