Fractional zinc absorption using a single isotope tracer

Fractional absorption of zinc (Zn) has been measured using dual isotopes of Zn given simultaneously. An oral test dose and an intravenous (i.v.) reference dose are administered, followed by the measurement of the double isotopic enrichment (E) in urine 48 h after administration. We postulated that an estimate of the %E in urine for a given i.v. dose of Zn may be used to eliminate the need for venipuncture and the second Zn isotope.

To determine a constant (k) for the Zn enrichment of urine after i.v. administration of a dose of labeled Zn in Zn-replete subjects. To use 'k' to calculate fractional absorption of Zn, and to compare these values to values obtained using the standard dual isotope method.

Single-arm cohort.

The Hospital for Sick Children, Toronto, Canada.

Twenty-three healthy adults were recruited from the Metropolitan Toronto area. Seventeen subjects completed the study.

A 2.29 mg i.v. dose of (67)Zn followed immediately by a 2.50 mg oral dose of (70)Zn.

Population mean percentage enrichment (%E) of (67)Zn in urine was 1.43 (95% CI 1.26, 1.60). The ratio of the i.v. dose to mean %E in urine (k) was estimated to be 1.60 mg (95% CI 1.43, 1.82). There was no difference in the mean fractional absorption of Zn calculated using the single compared to the dual isotope method: 12.58% (95% CI 2.22, 22.94) vs 12.68% (95% CI 4.52, 20.85), respectively (P=0.89). The correlation coefficient between the two methods was 0.81 (P<0.0001).

The dual isotope method may be replaced by using a constant (k) and a single oral dose of isotopic-enriched Zn to estimate fractional absorption of Zn within a population.

Gerber Products Company, Fremont, MI.