Comparison of iohexol and lactulose-mannitol tests as markers of disease activity in patients with inflammatory bowel disease

Increased intestinal permeability has been proposed as one aetiological fac tor for inflammatory bowel diseases (IBD). We have previously found that in testinal permeability of a water-soluble contrast medium, iohexol, correlat es with disease activity. The objective was to compare the iohexol test wit h the lactulose-mannitol ratio, which is a more extensively studied permeab ility marker, in patients with active IBD. Urinary excretion of iohexol was compared to the lactulose-mannitol ratio in 22 patients with an exacerbati on of IBD and in 10 healthy controls. Median intestinal absorption of iohex ol was 0.64% (range 0.13-3.8%) in the 22 patients and 0.3% (range 0.15-0.54 %) in the controls (p = 0.016), whereas the median lactulose-mannitol ratio was 0.037 (range 0.01-0.260) in patients and 0.03 (range 0.004-0.063) in c ontrols (N.S.). Correlation between urinary excretion of iohexol and lactul ose-mannitol ratio was positive (R = +0.41, p = 0.018). The urinary excreti on of iohexol correlated positively with endoscopic disease activity (R = 0.74, p < 0.001) and the modified Harvey-Bradshaw index (R = +0.44, p = 0. 04). The lactulose-mannitol ratio correlated positively with endoscopic dis ease activity (R = +0.44, p = 0.05), but correlations with clinical index o r c-reactive protein were poor. In conclusion, the iohexol test is a superi or activity marker compared to the lactulose-mannitol ratio which probably reflects, instead, some pathogenic property of IBD.