Accuracy of simple techniques for estimating fractional zinc absorption in humans

The theoretical basis of the accuracy of a number of simple techniques for estimating fractional zinc absorption (FZA) in humans using stable isotopic tracers has not been evaluated. These techniques include fecal monitoring (FM), deconvolution analysis (DA), double isotopic tracer ratio (DITR) and indicator dilution methods. Using a compartmental model, we investigated the accuracy and logic of each of these techniques. Time-dependent estimates of FZA based on the simple techniques were simulated using the compartmental model and compared with the known FZA derived from the model. The analysis elucidated logical errors in some of the FM techniques, and even when these problems were corrected, the FM technique was still prone to errors due to incomplete fecal tracer recovery and variable gastrointestinal (GI) transit time. Although logically correct, the indicator dilution techniques were also highly sensitive to incomplete fecal tracer recovery and variable GI transit time. The DA and DITR techniques were the most robust in that they were logically correct and were insensitive to incomplete fecal tracer recovery and variable GI transit time. Although all of the DA and DITR methods provided similarly good estimates of FZA relative to the compartmental model, the DITR technique performed on a spot urine specimen obtained several days after tracer administration was the preferred choice because of its simplicity and minimal requirements for patient compliance.