AIM:To investigate whether microproteinuria in patientswith inflammatory bowel disease(IBD)is associated withthe disease activity or the treatment with 5-aminosalicylicacid(5-ASA).METHODS:We prospectively studied microproteinuriain 86 consecutive patients with IBD,61 with ulcerativecolitis(UC)and 25 with Crohn’s disease(CD),before aswell as 2 and 6 months after their inclusion in the study.Forty-six patients received 5-ASA for a period of 28.8months(range 1-168 mo).Microalbuminuria(mALB)andurine levels of the renal tubular proteins β_2-microglobulin(β_2mGLB)and β-N-acetyl-D-glucosamidase(β-NAG)aswell as the creatinine clearance were determined in a12-h overnight urine collection.Tumor necrosis factor-a(TNF-α)serum levels were also measured.RESULTS:A total of 277 measurements(194 in UCpatients and 83 in CD patients)were performed.Theprevalence of abnormal microproteinuria in UC and CDpatients was 12.9% and 6.0% for mALB,22.7% and27.7% for β_2mGLB,and 11.3% and 8.4% for β-NAG,respectively,mALB was not associated with IBD activity.β_2mGLB and β-NAG urine levels were correlated to UCactivity (UCAI:P<0.01;UCEI:P<0.005).mALB in UCpatients and β-NAG urine levels in CD patients wererelated to TNF-α serum levels.An association wasnoticed between microproteinuria and smoking habit.Treatment with 5-ASA was not correlated to the severityof microproteinuria or to the changes of creatinineclearance. CONCLUSION:Microproteinuria is mainly associatedwith UC and its activity but not affected by 5-ASA. AIM: To investigate whether microproteinuria in patients with inflammatory bowel disease (IBD) is associated with the disease activity or the treatment with 5-aminosalicylic acid (5-ASA). METHODS: We prospectively investigated microproteinuriain 86 consecutive patients with IBD, 61 with ulcerative colitis and 25 with Crohn’s disease (CD), before aswell as 2 and 6 months after their inclusion in the study. Forty-six patients received 5-ASA for a period of 28.8 months (range 1-168 mo). Microalbuminuria (mALB) andurine levels of the renal tubular proteins β_2-microglobulin (β_2mGLB) and β-N-acetyl-D-glucosamidase (β-NAG) aswell as the creatinine clearance were determined in a12-h overnight urine collection. Tumor necrosis factor- α) serum levels were also measured. RESULTS: A total of 277 measurements (194 in UCpatients and 83 in CD patients) were performed. Theprevalence of abnormal microproteinuria in UC and CDpatients was 12.9% and 6.0% for mALB, 22.7% and27.7 % for β_2mGLB, and 11.3% and 8.4% for β-NAG, resp MALB in UC patients and β-NAG urine levels were correlated with UC activity (UCAI: P <0.01; UCEI: P <0.005) -α serum levels. An association wasnoticed between microproteinuria and smoking habit. Treatment with 5-ASA was not correlated to the severity of microproteinuria or to the changes of creatinineclearance. CONCLUSION: Microproteinuria is mainly associated with UC and its activity but not affected by 5-ASA .