Brookhaven National Laboratory Report BNL-6822

The evaluation of iron absorption using a single crystal whole-body counter is complicated by the inherent difficulty of determining a correct "100% value". Shortly after ingestion, tracer radioiron can be found in the stomach, upper small intestine, portal circulation and liver. Fourteen to twenty days later, the time at which absorption is measured most effectively, the radioiron will be distributed between the red cell mass, liver, spleen, bone marrow and other storage areas. With this mixed distribution there will always be an error because of geometric factors, and hence in counting efficiency, in using the relationship of [formula not transcribed] to calculate iron absorption. In a previous iron absorption study reported from this group, the radioiron retention measured 4 to 10 hours postingestion was used as the "100% value". The present experiments were designed to evaluate the clinical usefulness of the 4 hour postingestion count as the "100% value" as compared to the immediate postingestion body count, and to compare these values with an intravenous Fe59 calibrated absorption. These studies were performed with the realization that there is no absolute solution to the problem