Double isotope tracer method for measuring fractional zinc absorption: theoretical analysis

Abstract

Several approaches for estimation of fractional zinc absorption (FZA) by calculating the ratio of oral to intravenous stable isotopic tracer concentrations (at an appropriate time) in urine or plasma after their simultaneous administration have been proposed in the last decade. These simple-to-implement approaches, often referred to as the double isotopic tracer ratio (DITR) method, are more attractive than the classical “deconvolution” method and the more commonly used single-tracer methods based on fecal monitoring and indicator dilution, after oral or intravenous tracer administration, respectively. However, the domain of validity of DITR for measuring FZA has recently been questioned. In this paper, we provide a theoretical justification of the validity of four different “approximate” formulations of the DITR technique by demonstrating mathematically that their accuracy is a consequence of the particular properties of zinc kinetics.

Measurement of Zinc Absorption From Meals: Comparison of Extrinsic Zinc Labeling and Independent Measurements of Dietary Zinc Absorption

“…We have already had reassurance that results using our dual isotope tracer ratio (DITR) technique based on measurements of isotopic enrichment in urine [12–15] for measuring absorption of extrinsic zinc label compare well with results of other techniques, including deconvolution and data obtained from compartmental modeling [22]. The other major question is whether our extrinsic labeling technique provides an accurate measure of the absorption of dietary zinc that has been extrinsically labeled.…”

“…NAZ was determined from the difference between total dietary zinc and total fecal zinc for the 6-day metabolic period. FAZ extrinsic was determined by a dual isotope tracer ratio technique (DITR) [12–15], in which extrinsic zinc stable isotope label was administered with each meal for the same 6-day period. The study timeline is summarized in Figure l.…”

Zinc Absorption by Young Adults from Supplemental Zinc Citrate Is Comparable with That from Zinc Gluconate and Higher than from Zinc Oxide

“…It is recommended as the method of choice for determination of fractional zinc absorption (12, 13, 15, 19). The technique applied to a spot urine specimen is easy to implement and not sensitive to participant compliance.…”

Changing the zinc:iron ratio in a cereal-based nutritional supplement has no effect on percent absorption of iron and zinc in Sri Lankan children

“…We collected only a single spot urine collection at 2 d after isotope dosing to assess Zn absorption, which we believe is adequate for this purpose. Sparacino et al ( 39 ) have shown that this is mathematically equivalent to measuring the isotopes in a single serum sample. As such, it slightly underestimated true Zn absorption.…”