Unbound iron binding capacity (UIBC) as a test for empty iron stores – results from the HUNT Study

Abstract

Background. When s-iron and s-transferrin are used to diagnose empty iron stores, the measurements are usually combined in the calculation of s-transferrin saturation. This may not be the best way to utilize the information in s-iron and s-transferrin, as s-transferrin alone has a better diagnostic accuracy than s-transferrin saturation. We suggest that unbound iron binding capacity (UIBC), which is s-total iron binding capacity (2 times s-transferrin) minus s-iron could be used for diagnosing empty iron stores. Methods. To test this hypothesis, we used 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 3029 women of childbearing age. Empty iron stores were defined as s-ferritin less than 10 μg/L or less than 15 μg/L. Results. At both definitions of empty iron stores s-UIBC had a better diagnostic accuracy than the other tests, with area under the ROC curve of 0.80–0.87. This was also the trend in a subpopulation of 172 anemic women, where the area under the ROC curve of s-UIBC was 0.92. 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 is calculation of s-transferrin saturation.

Key Words::

• Diagnostic tests
• iron deficiency anemia
• ROC curve
• sensitivity and specificity
• transferrin

Acknowledgements

The Nord-Trøndelag Health Study (The HUNT Study) is a collaboration between HUNT Research Centre (Faculty of Medicine, Norwegian University of Science and Technology NTNU), Nord-Trøndelag County Council, Central Norway Health Authority, and the Norwegian Institute of Public Health.

Declaration of interest: The authors report no conflict of interest. The authors alone are responsible for the content and writing of the paper.