Fecal monitoring iron absorption measurements

Two critical aspects of fecal monitoring for absorption determinations are complete collection of unabsorbed isotopes and sample homogeneity. The times required for complete collections of unabsorbed isotopes vary markedly between subjects and also within the same subject. Therefore fecal makers are required to assure complete collections (9). The times required for complete elimination of a fecal marker have ranged from 6 to 18 days and included from 3 to 23 fecal samples in the experiments discussed later in this paper. Collection of only 80% of unabsorbed isotopes, particularly when absorption is low, will result in serious overestimation of absorption. In the case of iron, absorption of only 10% would appear to be nearly 3(, if 20% of the unabsorbed iron was not collected. A marker such as PEG, which can be measured quantitatively, must be used. Stools are collected until no trace of the inert marker can be detected. Recovery of less than 90% of the PEG... 

Results from some recent studies (19-36) on the effects of fiber are summarized in Table I. For the most part, the results are from multi-day balance studies. However, Turnland et al. (36) used the stable isotope fecal monitoring method to assess zinc utilization and Simpson et al. (24) measured iron absorption from a single test meal. 

The aim of this study was to further explore the potential and limitations of using stable iron isotopes as tracers and EI-MS in absorption studies. Procedures were developed for preparing iron acetylacetonate from both blood and fecal samples for mass spectrometric analysis. The precision and accuracy of ion abundance measurements were evaluated. In vivo use of stable iron isotope tracers was tested with a human study in which 54pe and 57pe were given orally and absorption was estimated with the fecal monitoring and hemoglobin incorporation methods. 

Table VII. Absorption of stable iron isotopes in orange juice measured with the fecal monitoring and hemoglobin incorporation...

Errors associated with iron quantification and abimdance measurements are common to both fecal monitoring and hemoglobin incorporation methods According to Janghorbani and Young (2 )> acceptable absorption estimates can be obtained if the precision of these measurements is kept below 5% The analytical procedures developed in this study are thus considered satisfactory since the relative standard deviation was 2 48% for total iron quantification and less than 2% for ion abimdance determinations ... 

---