Comparison of radio-opaque pellets and chromium sesquioxide as inert markers in studies requiring accurate faecal collections.

Radio-opaque pellets (ROP) similar to those currently used to measure gastrointestinal transit time have been compared with chromium sesquioxide to assess their suitability for use as inert markers in the gut. Five healthy subjects took both markers with every meal for two separate three week periods while taking metabolically controlled diets. Overall recovery of both markers was satisfactory; ROP 99.7 +/- 0.3% (SD) and chromium 97.8 +/- 1.6% (SD). A comparison of the amount for each marker recovered in 69 separate faecal collection periods of various lengths showed close agreement (R = 0.99) and the tail-off in marker excretion after cessation of ROP and chromium intake was similar, although slightly more prolonged for chromium. The amount of marker retained in the gut was 13.5% greater for chromium at the end of the three week study periods. Both markers proved satisfactory for correcting variations in faecal calcium output. The ROP, however, offer clear advantages over chromium in that they are considerably easier and quicker to measure, the method of measurement using x-rays does not alter the stools and faecal handling is minimised. The precision of ROP measurement is greater and, because of the variety of ROP available, they offer more flexibility for metabolic studies. In addition, stool by stool analysis is possible enabling simultaneous measurement of mean transit time to be made in experimental subjects.