Low-dose oral iron absorption test: establishment of a reference interval

The low-dose oral iron absorption test (OIAT), a possible test for iron deficiency, is based on the fact that intestinal iron absorption is higher in iron-deficient subjects than in those with normal or increased iron stores. The aims of this study were to establish a reference interval for the OIAT, to evaluate five different ways of presenting the results, and to advocate for the use of one of these methods. OIAT was performed in 122 healthy volunteers, 3 of whom were excluded as a result of technical difficulties. The volunteers were given 10 mg of oral iron sulphate at 0900 h on an empty stomach. S-iron was measured just before iron consumption, and after 1, 2 and 3 h. The maximum increase in S-iron during the test, presented as Cmax (micromol l(-1)), was higher in females (5 [median]; 3 and 7 [1st and 3rd quartiles]; 0-34 [range]) than in males (3; 1 and 5; 0-13) (p<0.001 Mann Whitney U-test). Furthermore, Cmax was significantly higher in females aged 22 44 years than in all other age groups (males and females), but did not fluctuate significantly with age in males. Cmax was higher in premenopausal than in postmenopausal females (6; 5 and 10; 0-34 and 4; 2 and 5; 0-12, respectively) (p <0.01 Mann Whitney U-test). In conclusion, iron absorption assessed by the OIAT was higher in premenopausal females than in postmenopausal females and males. We suggest reference intervals of 0-34 micromol l(-1) in premenopausal females, and 0-11 micromol l(-1) in all other persons, i.e. males and postmenopausal females.