To evaluate diagnostic accuracy of ultrasonography in comparison with colonoscopy as gold standard for diagnosing of ulcerative colitis (UC).

In this prospective study, 114 participants who attended in Ahvaz Imam Hospital during March 2014 to February 2015 included. The participants divided into 2 groups: group A as 64 UC patients (flare or new case) and 50 participants as control group who attend for colorectal cancer screening or evaluation of rectorrhagia. All of the participants obtained a Trans abdominal ultrasonography after 8 hours fasting and evaluated for colonic thickness in any involved region, loss of compressibility, peristaltic movement, mesenteric lymph nodes enlargement and presence or absence of ascites, fat stranding or stratification.

Ultrasonography sensitivity for diagnosing of moderate to severe UC in comparison with colonoscopy was between 52.56 to 86.36% based on different factors such as new onset or active disease, BMI, gender and region of involvement. In all of the situations the specificity was 100%. The sensitivity for diagnosing new cases of UC and pancolitis were 86.36% and 76.67% respectively and these figures were less among cases with BMI more than 25. The colonic wall thickness in new cases of UC (6.4 ± 1.3mm) was significantly more than wall thickness among disease flare up (5.5 ± 1.7mm) (P = 0.02) and also average colon thickness in UC group (average 5.9mm , range 2-9mm) was significantly more than control group (average 3.3mm, range 3-4 mm).

The findings of current study prove that ultrasonography is not an ideal tool for evaluation of UC patients because its results could affect by several factors such as BMI and region of involvement.