Unit Converter
Iron Binding Capacity,Unsaturated (UIBC)
Synonyms
- UIBC
- Unsaturated iron-binding capacity
- Latent iron-binding capacity
- Reserve iron-binding capacity
- Unbound transferrin capacity
Units of Measurement
- mmol/L
- µmol/L
- µg/dL
- µg/100 mL
- µg%
- µg/L
- ng/mL
Key Conversions
1 µg/dL = 0.179 µmol/L
1 µmol/L = 55.85 µg/L
1 ng/mL = 1 µg/L
µg% = µg/dL
mmol/L = µmol/L ÷ 1000
UIBC is measured as an iron mass equivalent, not transferrin mass.
Description
UIBC represents the unused iron-binding capacity of transferrin.
This means:
- How much transferrin is empty
- How much iron can still be carried
- The reserve binding capacity
It is mathematically related to TIBC and serum iron:
UIBC = TIBC – Serum Iron
UIBC is crucial for calculating:
Transferrin Saturation (TS%)
\text{TS%} = \frac{\text{Iron}}{\text{TIBC}} \times 100
Physiological Role
Transferrin is the main transporter of circulating iron.
UIBC helps quantify:
- How saturated transferrin is
- How much iron-binding reserve remains
- Ability of body to buffer free iron
UIBC falls when transferrin is more saturated, as seen in iron overload.
UIBC rises when transferrin is less saturated, as in iron deficiency.
Clinical Significance
HIGH UIBC
1. Iron Deficiency / Iron Deficiency Anemia
- Transferrin production rises
- Transferrin saturation decreases
- Serum iron is low
→ Leaving a large unsaturated capacity
Typical UIBC: >300–350 µg/dL
2. Pregnancy
UIBC rises due to increased transferrin, especially in 2nd–3rd trimester.
3. Oral Contraceptive Use
Estrogen increases transferrin → higher UIBC.
LOW UIBC
1. Hemochromatosis
Low UIBC + high TS% (>45–60%) is a hallmark.
2. Iron Overload States
- Transfusional overload
- Thalassemia major
- Sideroblastic anemia
- Ineffective erythropoiesis
→ High serum iron saturates transferrin → low UIBC
3. Chronic Inflammation / Chronic Disease
- Low transferrin synthesis
- Low TIBC
→ Reduced UIBC
4. Liver Disease
Reduced transferrin synthesis (cirrhosis) → low UIBC.
5. Malnutrition
Low protein synthesis results in low transferrin and low UIBC.
6. Nephrotic Syndrome
Protein loss → low transferrin → low UIBC.
Reference Intervals
Adults
- UIBC: 150 – 375 µg/dL
(= 26.8 – 67.1 µmol/L)
Children
- UIBC: 140 – 300 µg/dL
Interpretive Values
- >375 µg/dL → Iron deficiency likely
- <150 µg/dL → Iron overload, inflammation, or liver disease
- <100 µg/dL → Strongly suggestive of iron overload (hemochromatosis)
Diagnostic Uses
1. Evaluate Iron Deficiency
High UIBC + low iron + high TIBC = classic IDA.
2. Iron Overload Workup
Low UIBC + high iron → hemochromatosis.
3. Calculate Transferrin Saturation (TS%)
Low UIBC → high TS%
High UIBC → low TS%
4. Assess Chronic Disease Anemia
Low iron + low TIBC + low UIBC.
5. Monitor Iron Therapy
UIBC decreases as iron stores improve.
Analytical Notes
- Fasting morning sample recommended (iron is diurnal)
- Avoid iron supplements for 24 hrs
- Hemolysis may falsely increase serum iron → falsely reduce UIBC
- UIBC is calculated using excess iron added to serum in the assay
Clinical Pearls
- UIBC increases before serum ferritin falls in early iron deficiency.
- In iron deficiency anemia:
- Iron ↓
- TIBC ↑
- UIBC ↑↑
- TS% ↓
- Iron ↓
- Low UIBC is an important marker for hemochromatosis, especially if transferrin saturation >50%.
- UIBC is more reliable than serum iron alone, which fluctuates widely.
Interesting Fact
Transferrin is normally only 20–45% saturated, leaving a large “reserve”-measured as UIBC-to protect tissues from iron toxicity.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Iron Studies.
- ACG/BSG Guidelines - Iron Deficiency Anemia.
- WHO - Iron Deficiency Reference Standards.
- Mayo Clinic Laboratories - UIBC.
- ARUP Consult - Iron Studies Interpretation.
- MedlinePlus / NIH - Iron Tests.