To see whether intestinal permeability (IP) predicted relapse in Crohn
's disease, we measured IP in 72 patients with quiescent Crohn's disea
se using the lactulose-mannitol test. The permeability index (lactulos
e/mannitol) was significantly higher in patients than in controls (0.0
46 [SEM 0.005] vs 0.018 [SEM 0.002], respectively). Patients were foll
owed for 1 year after the test. 26 of the 37 patients with raised perm
eability, but only 6 of the 35 with normal permeability relapsed withi
n 1 year after the test (p<0.001). The sensitivity of the permeability
test as a predictor for relapse was 81%. A significant correlation wa
s found between the value of the permeability index and the probabilit
y of relapse (p<0.01). These results show that increases in intestinal
permeability precede clinical relapses in Crohn's disease and so are
an indicator of subclinical disease. The measurement of intestinal per
meability may lead to a better understanding of the pathogenesis of Cr
ohn's disease.