EFFECT OF REHYDRATION ON GUAIAC-BASED FECAL OCCULT BLOOD TESTING IN COLORECTAL-CANCER SCREENING

Screening for colorectal cancer by means of unhydrated Hemoccult (HO) is in progress in the Province of Florence since 1982. In 1990 rehydra ted HO was introduced in the town of Empoli. Five adjacent municipalit ies where screening had started in 1987 were selected for comparison. In both areas subjects aged 40-70 were invited by mail to undergo the screening protocol. HO-positive subjects were invited to undergo eithe r pancolonoscopy or a combination of left colonoscopy and double contr ast barium enema. HO-negative subjects were invited to repeat screenin g 2 years later. The positivity rate of HO was significantly higher (P < 0.001) for rehydrated (5%) as compared to unhydrated (3.1%) HO. The positive predictive values for cancer (unhydrated: 5.8%; rehydrated: 8.9%) and for adenomas (unhydrated: 26.7%; rehydrated: 25.5%) did not significantly differ. The detection rates of rehydrated HO were signif icantly higher as compared to unhydrated HO both for cancer (0.37% vs 0.15%; P < 0.05) and adenomas (1.06% vs 0.72%; P < 0.05 %). In the pre sent experience rehydration doesn't produce any decrease in the positi ve predictive value for cancer or adenomas and the increase in the pos itivity rate appears quite acceptable when considering the significant increase in the detection rates of cancer and adenomas. We conclude t hat rehydrated HO should be introduced as the standard test for screen ing in order to increase sensitivity for colorectal cancer and adenoma s.