Incomplete fecal collection

To determine iron absorption with tracers, a known amount of an iron tracer is given orally either by itself or with a meal. The appearance of the tracer, either in the feces or in whole blood, is monitored. In the fecal monitoring method, the feces are collected quantitatively. The collection period may last from as few as 3 (5) to as long as H days (6). Iron absorption is then estimated from the difference between the total amounts of tracer ingested and excreted. Probably, the most common and serious error in this method is introduced by incomplete fecal collection. 

Variability in Absorption Estimates In this study, the occurrence of a negative absorption value for one subject and the absence of a significant vitamin C effect raise some questions about the accuracy of the method However, the expected changes in absorption due to dietary treatments may be masked by the analytical variations associated with absorption measurements and biological variabilities of iron absorption Analytical variations can be introduced at several stages of the analytical procedures incomplete fecal collection, inhomogeneous samples, iron contamination, incomplete colorimetric reaction, non-quantitative recovery after chemical ashing, and variations in isotopic measurements due to ion statistics, memory effects, instrument drift, etc Some of these are not as serious as others, for example, contamination with natural iron woiold not affect the estimate of tracer concentrations provided it occurs before the total iron content is measured ... 

At the end of an extensive survey of hospital laboratories in the UK, Duncan (unpublished report of the CUnical Resource and Audit Group, Scottish Office, Edinburgh 1997) concluded that .., the current utilization of the test, with no control of dietary fat intake, no correction for incomplete fecal collections and misgivings over analytical reliability, makes it a highly unsatisfactory investigation and probably of little clinical value. ... 

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