What is the difference between Unbound Iron-Binding Capacity (UIBC) and Total Iron-Binding Capacity (TIBC)?

From the Guidelines

TIBC is the more reliable and commonly used test to evaluate iron status in the body, as it measures the total amount of iron that transferrin can bind, whereas UIBC measures the portion of transferrin that is not carrying iron. When evaluating iron status, it's essential to consider both TIBC and UIBC, as well as serum iron and ferritin levels.

• TIBC measures the total amount of iron that transferrin, the main iron-carrying protein in blood, can bind.
• UIBC measures the portion of transferrin that is not carrying iron, or the "unsaturated" binding capacity. The relationship between TIBC and UIBC is straightforward: TIBC = Serum Iron + UIBC, as noted in studies such as 1. These tests are typically ordered together with serum iron and ferritin to assess iron deficiency or iron overload conditions.
• In iron deficiency, TIBC is often elevated while serum iron is low, resulting in a high UIBC.
• Conversely, in iron overload conditions like hemochromatosis, TIBC may be normal or low while serum iron is high, resulting in a low UIBC. The transferrin saturation percentage, calculated as (Serum Iron ÷ TIBC) × 100, is a useful derived value that helps interpret these results, with normal values typically ranging from 20-50%, as discussed in 1. Values below 20% suggest iron deficiency, while values above 50% may indicate iron overload. It's also important to note that factors other than iron status can affect TIBC results, such as inflammation, chronic infection, malignancies, liver disease, nephrotic syndrome, and malnutrition, as mentioned in 1. Therefore, when interpreting TIBC and UIBC results, it's crucial to consider the patient's overall clinical context and other laboratory findings, such as serum ferritin levels, which reflect total body iron stores, as noted in 1.

From the Research

UIBC vs TIBC

• UIBC (Unsaturated Iron Binding Capacity) and TIBC (Total Iron Binding Capacity) are two related but distinct measures used to assess iron status in the body 2.
• TIBC measures the total amount of iron that can be bound by transferrin, a protein that transports iron in the blood, while UIBC measures the amount of iron that can still be bound by transferrin after accounting for the amount of iron already present in the blood 2.
• In the context of iron deficiency anemia, TIBC is often elevated, indicating an increased capacity for iron binding, while UIBC is also elevated, indicating an increased ability to bind iron 3, 4.
• The measurement of TIBC and UIBC can be useful in distinguishing between iron deficiency anemia and anemia of chronic disease, as well as in monitoring the response to iron supplementation therapy 4.
• However, it is essential to interpret these measures in conjunction with other laboratory tests, such as ferritin and transferrin saturation, to obtain a comprehensive understanding of iron status 2.