Patients with ankylosing spondylitis and healthy relatives do not show increased small intestinal permeability with the lactulose-mannitol test.

Small intestinal permeability was measured in 71 subjects: 26 (24 B27+) patients with ankylosing spondylitis (AS); 20 healthy first degree relatives (13 B27+); 6 patients with active Crohn's disease and 19 healthy controls. We determined the urinary excretion ratio of two ingested sugar probes, lactulose (10 g) and mannitol (0.5 g) by gas-liquid chromatography. The median lactulose/mannitol excretion ratio in AS patients (0.0099) and relatives (0.0090) was not significantly different from the median ratio in healthy controls (0.0095). HLA status or use of NSAIDs did not significantly influence the results. In patients with Crohn's disease, on the other hand, the median lactulose/mannitol ratio (0.021) was significantly increased in comparison to healthy controls (0.0095). Our results confirm that the lactulose-mannitol test can be used to demonstrate increased intestinal permeability in Crohn's disease. For patients with AS and their relatives the lactulose-mannitol test may not be sufficiently sensitive. Alternatively, significantly increased permeability may not occur in most patients with AS.