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 factor for inflammatory bowel diseases (IBD). We have previously found that intestinal permeability of a water-soluble contrast medium, iohexol, correlates with disease activity. The objective was to compare the iohexol test with the lactulose-mannitol ratio, which is a more extensively studied permeability marker, in patients with active IBD. Urinary excretion of iohexol was compared to the lactulose-mannitol ratio in 22 patients with an exacerbation of IBD and in 10 healthy controls. Median intestinal absorption of iohexol 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 controls (N.S.). Correlation between urinary excretion of iohexol and lactulose-mannitol ratio was positive (R = +0.41, p = 0.018). The urinary excretion 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 disease activity (R = +0.44, p = 0.05), but correlations with clinical index or c-reactive protein were poor. In conclusion, the iohexol test is a superior activity marker compared to the lactulose-mannitol ratio which probably reflects, instead, some pathogenic property of IBD.