Can a double isotope method be used to measure fractional zinc absorption from urinary samples?

Abstract

Objective: This study was designed to test whether fractional absorption calculated from urinary enrichment of stable isotopes of zinc accurately re¯ects true absorption measured by faecal monitoring. Design: The two techniques were directly compared in volunteers, whereby each subject acted as his/her own control. Setting: Volunteers were healthy adults, living at home, who were taking part in a larger study on zinc. They attended the local hospital for isotope administration. Subjects: Fifteen volunteers were recruited, seven of whom had non-insulin dependent diabetes mellitus. All completed the study, but ®ve did not carry out a complete faecal collection. Interventions: Each subject received an oral and i.v. dose of different stable isotopes of zinc with breakfast. Faecal and urinary enrichment with the isotopes was measured. Results: There was no signi®cant correlation between the two measures of absorption. Conclusions: The double label stable isotope technique for determining zinc absorption from measurements of urinary enrichment does not reliably predict true zinc absorption (measured by faecal and urinary monitoring) in a heterogenous group of adults given relatively low doses of stable isotopes of zinc. Sponsorship: This work was funded by the European Commission (Training and Mobility Programme).

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

“…2, A and B. It is worth noting that the order of the (linear) dynamic system originating 70 z 1 (t) is 5 [the state variables corresponding to compartments 4,6,8, and 9 do not play any role in 70 z 1 (t)], whereas that of the system that generates 67 z 1 (t) is 6 (the input occurs in compartment 4). Indeed, the (early) time course in plasma of 67 Zn-tr reflects the first-pass kinetics of movement through and absorption from the gastrointestinal tract.…”

“…The fecal monitoring method, employing a single oral tracer with measurement of the tracer in each fecal sample, can provide an accurate estimate of FZA if the kinetics of tracer absorption can be separated from the kinetics of secretion of absorbed oral tracer, a problem not yet completely solved (9). Friel et al (3) found "good agreement" between the two methods, but Rautscher and Fairweather-Tait (8) concluded that DITR does "not reliably predict" FZA. On the basis of a number of experimental and simulation considerations, we believe that the fecal monitoring method is an inappropriate reference for assessing DITR (5,9).…”

“…THE VALIDITY of the double isotopic tracer ratio (DITR) method for measuring fractional zinc absorption (FZA) has recently been questioned (8). This method, first proposed by Friel et al (3) for measuring FZA, is a modification of the DITR method for determining the fractional absorption of calcium (2,10,11) from the ratio of oral to intravenous stable isotopic tracers in a 24-h pooled collection of urine after tracer administration.…”

“…The DITR method for determining FZA has recently been compared with the fecal monitoring method (8), a commonly used technique for estimation of FZA. The fecal monitoring method, employing a single oral tracer with measurement of the tracer in each fecal sample, can provide an accurate estimate of FZA if the kinetics of tracer absorption can be separated from the kinetics of secretion of absorbed oral tracer, a problem not yet completely solved (9).…”

Magnesium absorption from mineral water

“…This calculation is the same as that used in a stable isotope field, which was initially adapted from the radioisotope technique (Turnlund, 1989;Sandström et al, 1993). In order to validate this approach, the method using stable isotopes were systematically compared with the single labelling method corrected for faecal endogenous excretion (Friel et al, 1992;Rauscher et al, 1997;Lowe et al, 2000). We compared these approaches in humans in order to validate the double labelling method for MgA determination.…”