The diagnostic accuracy of unbound iron binding capacity (UIBC) as a test for empty iron stores

Abstract

Background. Unbound iron binding capacity (UIBC) in serum, which is s-total iron binding capacity (2 times s- transferrin) minus s-iron, may be a more accurate marker of empty iron stores than serum transferrin saturation. Previously we have shown this for healthy females of childbearing age. Methods. Now we used receiver operating characteristic (ROC) curve analysis to compare the diagnostic accuracy of s-iron, s-transferrin, s-transferrin saturation and s-UIBC in diagnosing empty iron stores in 29,251 female and 19,652 male outpatients. Empty iron stores were defined as s-ferritin less than 10, 15 or 20 μg/L. Results. At all definitions of empty iron stores s-UIBC had a better diagnostic accuracy than the other tests in both male and female outpatients, with an area under the ROC curve of 0.85–0.97. Also in subpopulations with elevated s-CRP or low b-hemoglobin s-UIBC was more accurate than the other tests. All tests performed better in males than in females, and generally they were more accurate in adults than in children. Conclusion. When diagnosing empty iron stores calculation of s-UIBC is a better way to utilize the information in s-iron and s-transferrin than the calculation of s-transferrin saturation.