total and segmental colonic transit time ( ctt ) can be assessed noninvasively using radio - opaque markers . , can also be used to differentiate between patterns of delayed colonic transit and to evaluate the response to treatment . several methods have been published , differing in the number of markers ingested , in the number of days markers are ingested and in the number and intervals of abdominal x - rays [ 4 , 7 ] . in this method , the patient swallows one capsule containing 10 radio - opaque markers at the same hour for six consecutive days . on the seventh day , a plain abdominal x - ray is obtained at the same hour as the capsules were swallowed . interpretation is based on the identification of markers in three regions as defined by bony landmarks and gaseous outlines [ 1 , 4 ] . by counting the markers in the right , left and rectosigmoid regions , total and segmental ctts can be calculated according to the formula : ctt ( in hours )  =  sum of markers    2.4 . a 16-year - old girl with a long history of urinary tract infections and functional constipation presented with deterioration of her defecation problems following influenza h1n1 . abdominal pain and painful defecation intensified , and the frequency of bowel movements decreased from once every day to twice a week , despite up to 80  g per day of polyethylene glycol 4000 . on physical examination multiple masses could be palpated bilaterally in the abdomen which is consistent with faecal retention . because of the refractory nature of her constipation , a ctt was performed as described above . total ctt was 124.8  h ( 52 markers ; upper limit of normal 62  h ) , segmental transit times being 33.6 , 16.8 and 74.4  h , respectively ( fig . 1plain abdominal x - ray during ctt study before bowel cleansing with klean - prep plain abdominal x - ray during ctt study before bowel cleansing with klean - prep the girl was admitted for bowel cleansing with 4  l of polyethylene glycol because her symptoms persisted while only clear liquids were seen passing , this treatment was repeated twice in the next week . back on high doses of oral polyethylene glycol ( 80  g per day ) , the girl continued to complain of abdominal pain combined with a low frequency of bowel movements . although on physical examination the bilateral masses could not be felt anymore , palpation of the abdomen was repeatedly extremely painful . two months after the first study , therefore , the marker study was repeated . now 42 markers were found retained , most of them in the right hemicolon , translating into a ctt of 110.8  h , segmental transit times being 72 ( right ) , 0 ( left ) and 28.8 ( rectosigmoid ) h ( fig .  2 ) . because this suggested the presence of a caecal fecaloma , we decided to perform colonoscopy , aiming at disimpaction of the faecal mass , preceded by standard bowel preparation with 4 l of klean - prep. to our surprise the entire colon was empty , while dozens of radio - opaque markers were found clustered in small groups into sticky mucus to all quadrants of the right hemicolon wall ( fig . no further endoscopic abnormalities were encountered , in particular no signs of mucosal disease at the site the markers were found . therefore , no biopsies were taken during the endoscopy . the abdominal pain subsided over the next few days , and oral laxative medication could eventually be lowered to 10  g of polyethylene glycol per day . 3radio - opaque markers sticking together to the caecum wall as seen during colonoscopy plain abdominal x - ray during ctt study 2  months after bowel cleansing radio - opaque markers sticking together to the caecum wall as seen during colonoscopy it can aid in the differentiation of defecation disorders such as functional constipation and functional non - retentive faecal soiling . it can also be used when history seems to be unreliable , for example in patients with eating disorders . studies in adults and children show a strong positive correlation between the severity of symptoms of constipation and ctt , a transit time of over 100  h in children being associated with a poorer outcome of chronic constipation after 1  year . a study in 25 constipated adults reported unchanged ctt with marker accumulation shifted to the distal colon , while in another study in 10 adults , bowel cleansing resulted in significant shortening of ctt , but with unchanged distribution of radio - opaque markers . this case report shows that markers do not always mix appropriately with faeces and therefore sometimes may not adequately reflect ctt . apparently , in an empty colon , the markers can be caught in mucus and stick to the colonic wall for a longer period , even when it is followed by the normal passage of faeces . looking back to the x - rays , the typical pattern of clustering of the markers should probably have been interpretated as a sign of entrapment . in conclusion , while ctt assessment using radio - opaque markers can be applied successfully in the investigation of defecation disorders , the results can not be accepted blindly . especially the clustering of many markers within narrow margins might point at entrapment of markers against the colonic wall .
we report a misleading outcome of colonic transit time ( ctt ) assessment in an adolescent girl with functional constipation . 
 we found prolonged total and right segmental ctt despite high doses of oral polyethylene glycol 4000 and repeated treatment with polyethylene glycol 
 electrolyte solution ( klean - prep ) by nasogastric tube . 
 a colonoscopy aiming at disimpaction of a possible faecal mass revealed an empty colon with dozens of radio - opaque markers adhered to the colonic wall . 
 this report shows that the result of a ctt can not be accepted blindly . 
 especially the clustering of many markers within narrow margins might point at entrapment of markers in mucus against the colonic wall .