Unit Converter
Iron Binding Capacity, Total (TIBC)
Synonyms
- Total iron-binding capacity
- TIBC
- Transferrin capacity
- Total iron-binding potential
- Indirect transferrin measurement
Units of Measurement
- mmol/L
- µmol/L
- µg/dL
- µg/100 mL
- µg%
- µg/L
- ng/mL
Key Conversions
TIBC is reported in iron mass equivalents, not protein mass.
1 µmol/L = 55.85 µg/L
1 µg/dL = 10 µg/L = 0.179 µmol/L
1 ng/mL = 1 µg/L
µg% = µg/dL
mmol/L = µmol/L ÷ 1000
Description
TIBC measures the maximum amount of iron that transferrin can bind in serum.
It reflects:
- Transferrin concentration
- Iron transport capacity
TIBC is NOT a direct measure of transferrin protein, but an indirect functional test based on iron binding.
TIBC is essential for interpreting:
- Iron deficiency
- Iron overload
- Transferrin saturation (TS%)
Physiological Role
Transferrin, the iron-binding protein:
- Carries iron through plasma
- Delivers iron to bone marrow for erythropoiesis
- Prevents free iron toxicity
- Maintains iron homeostasis via hepcidin regulation
TIBC is therefore a surrogate marker for:
- Transferrin availability
- Body’s iron-binding potential
Clinical Significance
HIGH TIBC
Most common cause → iron deficiency
1. Iron Deficiency / Iron Deficiency Anemia (IDA)
- TIBC > 400–450 µg/dL
- Transferrin is high because liver increases production to capture more iron.
2. Pregnancy
TIBC naturally rises.
3. Oral Contraceptive Use
Increases transferrin production.
4. Acute Hepatitis
Transient rise.
LOW TIBC
1. Anemia of Chronic Disease / Inflammation
- Cytokines suppress transferrin synthesis
- Low serum iron + LOW TIBC + normal/high ferritin
2. Chronic Liver Disease
Reduced protein synthesis.
3. Malnutrition / Protein Deficiency
Low transferrin production.
4. Nephrotic Syndrome
Loss of proteins including transferrin.
5. Hemochromatosis / Iron Overload
- Body reduces transferrin to limit iron transport
- TIBC low, transferrin saturation high (>45–50%)
6. Malignancy / Chronic infection
Suppression of transferrin synthesis.
Reference Intervals
Fasting morning sample recommended.
Adults
- 250 – 450 µg/dL
(= 44.8 – 80.6 µmol/L)
Children
- 250 – 425 µg/dL
Critical Patterns
- TIBC > 450 µg/dL → iron deficiency very likely
- TIBC < 200 µg/dL → inflammation, liver disease, or overload
- TIBC < 150 µg/dL → severe inflammatory suppression or significant liver failure
Diagnostic Uses
1. Iron Deficiency Diagnosis
TIBC ↑ early before hemoglobin drops.
2. Differentiate IDA vs Anemia of Chronic Disease
| Parameter | IDA | Chronic Disease |
| Iron | ↓ | ↓ |
| TIBC | ↑ | ↓ |
| Ferritin | ↓ | Normal/↑ |
| TS% | ↓ | ↓ |
3. Iron Overload Evaluation
Low TIBC + high TS% suggests:
- Hemochromatosis
- Ineffective erythropoiesis
- Transfusional overload
4. Liver Disease Assessment
Low TIBC helps indicate impaired hepatic protein synthesis.
5. Nutritional Status
Reflects protein-calorie malnutrition.
6. Pregnancy Workup
Elevated TIBC is physiological.
Analytical Notes
- Fasting sample preferred; iron is diurnal
- Avoid hemolysis (false high iron → impacts TIBC calculation)
- Iron supplements should be stopped 24 hours prior
- TIBC may be influenced by illness, hormonal status, liver function
Clinical Pearls
- TIBC acts as an inverse marker of iron stores: high in deficiency, low in overload.
- Pair TIBC with transferrin saturation (TS%) = (Iron/TIBC) × 100.
- Low TIBC with high ferritin = anemia of chronic disease, not iron deficiency.
- In hemochromatosis, TIBC is low but transferrin saturation is very high (>50–60%).
- TIBC is more reliable than transferrin concentration in many labs.
Interesting Fact
Transferrin can bind two iron atoms, but is normally only 20–45% saturated, leaving a large “buffer capacity”-which is what TIBC quantifies.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Iron & Transferrin.
- ACG/BSG Guidelines - Iron Deficiency Evaluation.
- WHO Iron Deficiency Anemia Recommendations.
- Mayo Clinic Laboratories - TIBC.
- ARUP Consult - Iron Studies Interpretation.
- MedlinePlus / NIH - Iron Studies.