Error analysis of classic colonic transit time estimates

Estimates of colonic transit times (CTT) through the three colonic segments , right colon, left colon, and rectosigmoid, are commonly based on radiopaq ue markers. For a given segment, CTT is usually calculated from just the nu mber of markers visible in that segment on abdominal X-rays. This procedure is only strictly valid for the theoretical, but unrealistic, case of conti nuous marker ingestion (i.e., not for a single or once-daily ingestion). CT T was analyzed using the usual estimate of the mean CTT of one marker and a lso using a new, more realistic estimate based on the kinetic coefficients of a three-compartment colonic model. We directly compared our compartmenta l approach to classic CTT estimates by double-marker studies in six patient s. We also retrospectively studied CTT in 148 healthy control subjects (83 males, 65 females) and 1,309 subjects with functional bowel disorders (irri table bowel syndrome or constipation). Compared with the compartmental esti mates, the classic approach systematically underestimates CTT in both popul ations, i.e., in patients and in healthy control subjects. The relative err or could easily reach 100% independent of the site of colonic transit delay . The normal values of total CTT are then 44.3 +/- 29.3 instead of 30.1 +/- 23.6 h for males and 68.2 +/- 54.4 instead of 47.1 +/- 28.2 h for females.