Vol. 282, Issue 3, E679-E687, March 2002
Double isotope tracer method for measuring fractional zinc
absorption: theoretical analysis
Giovanni
Sparacino1,
David M.
Shames2,
Paolo
Vicini4,
Janet C.
King3, and
Claudio
Cobelli1
1 Department of Electronics and Informatics, University of
Padova, 35131 Padua, Italy; 2 Department of
Radiology, University of California at San Francisco, San Francisco,
94143; 3 Western Human Nutrition Research Center, US Department
of Agriculture/Agricultural Research Service, University of
California at Davis, Davis, California 95616; and
4 Department of Bioengineering, University of Washington,
Seattle, Washington 98195
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.
kinetics; compartmental model; deconvolution
