A test to measure oral iron absorption and glucose tolerance simultaneously in 18 to 55 year old premenopausal women.

Background & Aims: Several methods are available to measure iron absorption (IA). The oral iron absorption test (OIAT) measures IA based on a change in serum iron (ΔSeFe) concentration after an oral iron dose. The objective of this study was to validate the OIAT by comparing it to the reference method of fractional iron absorption (FIA) using red blood cell incorporation of stable iron isotopes from a labeled iron dose. A second objective was to assess whether the OIAT could be done simultaneously with an oral glucose tolerance test (OGTT), since iron deficiency and glucose intolerance may coexist, especially among overweight individuals with low-grade inflammation.

Methods: In this prospective experimental study, 116 women were enrolled and IA was measured using two different approaches 1) FIA from a labeled test meal containing 6 mg of Fe and 2) the OIAT assessing ΔSeFe at 2 h after the intake of 100 mg oral iron, done simultaneously with an OGTT. Markers of iron status, glycaemia and inflammation, and serum hepcidin, were measured.

Results: Prevalence of anemia and iron deficiency (defined as low serum ferritin) were 21% and 14%, respectively. ΔSeFe during the OIAT-OGTT was positively associated with FIA (r = 0.578, p < 0.001). ΔSeFe was not significantly correlated with markers of glucose and insulin metabolism during the OIAT-OGTT.

Conclusions: The combined OIAT and OGTT method described here correlates well with FIA measured by stable iron isotopes, and could provide information on both IA and glucose tolerance in a single 2-h test, decreasing the burden on patients. clinicaltrials.gov (NCT03642223).