Assessment of Inter-Observer Agreement of Colonic Transit Time (Ctt) with Radiopaque Markers

Abstract

Purpose: Although CTT is commonly assessed using radiopaque markers (Sitzmarks® (SZ)), whether there is inter-observer agreement regarding its interpretation is unknown. This is important because these studies are often interpreted by radiologists & gastroenterologists. AIM: Examine the inter-observer agreement of CTT as assessed by investigators from multiple sites & by two independent investigators. Methods: In a prospective study, 146 subjects, 72 with chronic constipation (Rome II) & 74 healthy subjects were enrolled from 8 sites. On Day 1, subjects ingested a SZ capsule containing 24 markers & advised to continue usual diet & avoid drugs that affect motility. Abd. x-rays were obtained on day 2 (48 hrs) & day 5 (120 hrs) & each investigator reported the number of retained markers. Subsequently, two independent investigators, blinded to the site & day of x-ray, performed CTT analysis. Slow transit was defined as >5 markers on Day 5 xray. Inter-observer agreement analysis was performed. Results: 4/72 (6%) normals & 31/74 (42%) constipated had slow colon transit. For analytical purposes, all subjects were grouped as having normal or slow transit; 35 had slow transit & 111 had normal CTT. Among these, in 1 constipated & 1 normal subject there was disagreement between the two observer groups, but in the rest there was excellent agreement (kappa = 0.96), see Figure. The intra-class correlation for Day 2 x-ray was 0.987 & for Day 5 x-ray was 0.978. There was disagreement in the absolute marker count for Day 2 x-ray in 46/146 (32%) subjects & for Day 5 x-ray in 25/146 (17%) subjects.FigureConclusion: Although there were discrepancies in 17–32% of subjects regarding the absolute marker count, overall there was good inter-observer agreement for CTT assessment with SZ and for separating normal from slow transit. Thus, radiopaque marker technique appears to be quite reliable between observers.