Small intestine bacterial overgrowth does not correspond to intestinal inflammation in cystic fibrosis

Small intestine bacterial overgrowth (SIBO) has been reported in cystic fibrosis (CF) patients. However, the potential link to intestinal inflammation has not been studied so far. Therefore, we aimed to assess whether SIBO correlates with intestinal inflammation in CF patients.

As a preliminary study, we assessed whether calprotectin is detectable in sputum expectorated by 10 CF patients. Since significant immunoreactivity was documented, in the major study we have included exclusively CF subjects not expectorating sputum for at least two weeks. Fecal calprotectin was measured in 25 CF patients and 30 healthy subjects (HS). All CF subjects were tested for the presence of SIBO using the hydrogen-methane breath test (BT). According to obtained results CF patients were divided into SIBO positive and negative subgroups. Subsequently, the intensity of intestinal inflammation in both subgroups was compared.

Fecal calprotectin concentrations in CF patients (range: 1.8-302.5; median 80.0 mg/L) were significantly higher (p < 0.00001) than in HS (not detectable-15.5; 2.5 mg/L). Calprotectin levels were abnormal in 21 (84%) studied CF subjects and none of HS. Abnormal BT results were found in 10 (40.0%) of CF patients. Calprotectin concentrations in SIBO positive and negative patients did not differ.

Gastrointestinal inflammation is a frequent finding in cystic fibrosis patients. However, small intestine bacterial overgrowth does not seem to be the major or at least not the only determinant of intestinal inflammation. Indirect measures of intestinal inflammation in CF patients may give false positive results.