From the Guidelines
Unbound Iron-Binding Capacity (UIBC) is a measure of the reserve capacity of transferrin to bind additional iron in the bloodstream, representing the portion of transferrin not currently carrying iron and available to bind more iron if needed.
Definition and Purpose
UIBC is typically measured alongside total iron-binding capacity (TIBC) and serum iron levels to assess iron status in the body. The normal UIBC range is approximately 150-375 μg/dL, though reference ranges may vary between laboratories 1. This test is particularly useful in diagnosing conditions related to iron metabolism such as iron deficiency anemia (where UIBC is elevated) and iron overload disorders like hemochromatosis (where UIBC is decreased) 1.
Physiological Basis
The physiological basis for measuring UIBC relates to transferrin's role as the primary iron transport protein in blood; when iron stores are low, more unoccupied binding sites are available on transferrin molecules, resulting in higher UIBC values. Conversely, when iron levels are excessive, more transferrin binding sites are occupied, leading to lower UIBC values 1.
Clinical Utility
This test is often ordered alongside ferritin levels for a more comprehensive assessment of iron status. It's essential to consider that factors other than iron status can affect results from this test, such as inflammation, chronic infection, malignancies, liver disease, nephrotic syndrome, and malnutrition, which can lower TIBC readings, and oral contraceptive use and pregnancy can raise the readings 1.
Key Points
- UIBC measures the reserve capacity of transferrin to bind additional iron.
- It is used to assess iron status in the body, particularly in diagnosing iron deficiency anemia and iron overload disorders.
- UIBC values are influenced by the availability of unoccupied binding sites on transferrin molecules.
- The test is often used in conjunction with ferritin levels for a comprehensive assessment of iron status.
From the Research
Definition of UIBC
- Unbound Iron-Binding Capacity (UIBC) is a measure of the amount of iron that can be bound by transferrin in the blood [ 2 ].
- It is calculated by subtracting the serum iron concentration from the total iron-binding capacity (TIBC) [ 2 ].
Clinical Significance of UIBC
- UIBC is used as a marker for empty iron stores, and its diagnostic accuracy is better than other tests such as serum transferrin saturation [ 2 ].
- UIBC is also used to detect hereditary hemochromatosis, and its reliability is equal to that of transferrin saturation [ 3 ].
- In patients with iron overload, UIBC can be used to monitor the effectiveness of iron chelation therapy [ 4 ].
Measurement of UIBC
- UIBC can be measured using a fully automated method that involves saturating serum transferrin with an excess amount of iron, followed by the elimination of unbound iron using a chromogenic reagent [ 5 ].
- The measurement of UIBC can be standardized using a modified indirect iron saturation excess assay [ 6 ].