A simple method for measuring zinc absorption in man using a short-lived isotope (69mZn).

Using a short-lived isotope of zinc (69mZn) with a half-life of 13.9 hr, we have developed a simple test of zinc absorption. After an oral dose of isotope (50 muCi) with 2 mg of elemental zinc a plasma appearance curve was constructed from radioactivity determined in blood samples taken sequentially over 8 hr. Two week later an iv dose of isotope (25 muCi) was administered and a plasma disappearance curve was constructed. Absorption was calculated by computer analysis of appearance and disappearance curves using a deconvolution programme. Mean absorption in five normal subjects was 61% (range 41 to 79%). In three subjects given food with, or 1 hr before the isotope, absorption was delayed and reduced to less than 20% of the oral dose at 8 hr. This test of zinc absorption is simple to perform and, because the isotope has a short half-life, has the advantage of subjecting patients to only limited radiation.