Renal tubular proteinuria in patients with irritable bowel syndrome

OBJECTIVE: Irritable bowel syndrome (IBS) is a common condition that is poorly understood. We have previously demonstrated tubular protinuria in patients with inflammatory bowel disease. This study examined whether tubular proteinuria was a feature of IBS. METHODS: Eighty control subjects (male:female, 28:52; age range 20-65 years) and 21 patients with IBS (male:female, 9:12; age range 16-64 years) (not significant) were recruited. Patients with known renal disease, hypertension, diabetes or microbiological evidence of urinary infection were excluded. The IBS patients all fulfilled the ROME II criteria. None had preceding gastroenteritis. Urinary alpha1-microglobulin (alpha1-M) was measured in a second-voided morning urine sample and corrected for urinary concentration by measurement of creatine. Blood samples were analysed for haematochemical indices including C-reactive protein. Statistical analysis was by unpaired t test. RESULTS: None of the IBS patients were reclassified with inflammatory bowel disease over a 5-year follow up period. All had normal haematochemical parameters. Mean +/- standard deviation urinary alpha1-M concentrations were significantly higher in IBS patients than controls (IBS patients, 1.17 +/- 0.65 mg/mmol; controls, 0.75 +/- 0.36 mg/mmol; P < 0.01) and exceeded 1.5 mg/mmol (the upper reference limit) in seven patients. There was no difference in urinary alpha1-M concentrations in the diarrhoea-predominant and constipation-predominant groups (mean +/- standard deviation, 1.342 +/- 0.65 versus 0.76 +/- 0.48 mg/mmol; P = 0.062). CONCLUSIONS: Urinary alpha1-M concentration is commonly increased in IBS, suggesting the presence of renal proximal tubular injury.