Total Iron Binding Capacity (TIBC)

Sample for Total Iron Binding Capacity (TIBC)

1. Take blood (3 to 5 mL) to prepare the serum.
2. The early morning sample is preferred because of the diurnal variation in the iron concentration.
3. Take the sample in the morning (around 10 am) because the level of iron varies during the day.
4. The specimen may be collected as serum without anticoagulant.
5. Can use plasma with heparin.
6. Reject the hemolysed sample.

Precautions for Total Iron Binding Capacity (TIBC)

1. Do not use anticoagulants like oxalate, citrate, or EDTA, because these bind to iron and are unacceptable.
2. 12 hours of fasting is preferred.
3. Water intake is allowed.
4. Stop taking iron-containing supplements before 24 to 48 hours.

Purpose of the test (Indications) for Total Iron Binding Capacity (TIBC)

1. This is done to diagnose the anemias.
2. Other tests needed are Total iron and Transferrin.
3. This helps in iron metabolism.

Definition of Total iron binding capacity (TIBC):

1. TIBC measures the maximum amount of iron that can be bound to protein and transports iron in the blood.
2. The maximum amount is transferred as transferrin.

Definition of Transferrin:

1. Transferrin is a glycoprotein and is responsible for the transport of iron.
2. Transferrin transports iron throughout the body and carries it to the cells.
3. Transferrin functions are:
   1. Help in the production of hemoglobin.
   2. Helps to regulate the amount of iron in the body.
   3. It binds to iron and prevents damage to the cells and tissues.
   4. Transferrin measurement gives an idea about the body’s ability to transport and regulate iron.

Definition of transferrin saturation:

1. Transferrin saturation measures the percentage of transferrin molecule that is bound to iron in the blood.
2. Transferrin saturation is calculated by:
   1. Serum iron level / TIBC = result is multiplied by 100.

Definition of iron

1. Iron is the most abundant element on earth.
2. There is a trace amount in the living cells.
3. Most of the iron in humans is located in the porphyrin ring of heme.
4. Porphyrins are incorporated into:
   1. Hemoglobin.
   2. Myoglobin.
   3. Cytochrome.
   4. Peroxidase.
   5. Catalase.
5. There are iron-sulfur proteins like NADH dehydrogenase and succinate dehydrogenase.

Functions of iron

1. Iron is able to interact reversibly with oxygen.
2. By this action, it can function in an electron-transfer reaction.
3. The above function makes iron biologically indispensable.

Iron metabolism

1. It is the most abundant trace element in the body.
   1. 65% is bound to Heme.
   2. Iron concentration measurement refers specifically to the Fe ⁺⁺⁺ bound to the transferrin, not to the iron circulating as free hemoglobin in the blood.
2. Iron is constituents of:
   1. Heme.
   2. Hemoglobin.
   3. Methemoglobin.
   4. Myoglobin.
   5. Several enzymes.

Iron uptake:

1. Iron intake depends on a person’s age, sex, and body requirement.
2. Iron intake of 1 mg/day is sufficient for men and postmenopausal women.
3. Women during menses lose 20 to 40 mg of iron/per cycle, so they need 2 mg of iron per day.
4. During pregnancy, fetal demands, and subsequent breastfeeding, a total loss of 900 mg of iron occurs.
5. Iron demand during pregnancy and lactation reaches 3 to 4 mg/day.

Iron absorption:

1. A normal diet contains between 10 to 20 mg of iron per day.
   1. Only 5% to 10% of this amount is absorbed mainly in the duodenum and upper small intestine.
2. Iron is absorbed by the intestinal epithelium.
3. Iron is ingested in Fe⁺⁺⁺ form and is converted to Fe⁺⁺ form for absorption.
4. The conversion of Fe⁺⁺⁺ to Fe ⁺⁺ form takes place in the stomach, where gastric acid HCL provides the acidity to reduce the iron.
   1. A Ferriruductase enzyme on the brush border of the epithelial cells also reduces Fe ⁺⁺⁺ to Fe ⁺⁺ form.
   2. This Fe⁺⁺ form is transported into the cell by divalent metal transport (DMT) system.

Iron absorption depends upon various foods:

1. Ascorbic acid (vitamin C), sugars, and amino acids increase absorption.
2. Phosphates in eggs, cheese, and milk, oxalates and phytates in vegetables, and tannates in tea decrease iron absorption.
3. Milk and antacid bind to iron and reduce its absorption.
4. Vitamin reduces Ferric (Fe+++) iron to Ferrous (Fe⁺⁺) by vitamin C, and the ferrous form is absorbed very easily.

Loss of iron:

1. Iron 1 mg/day is lost in the urine, sweat, bile, and shedding of skin epithelial cells.
2. This absorbed iron attaches to the blood’s transport protein (Transferrin).
3. So transferrin may indirectly represent the TIBC.

Ferritin

1. Definition:
   1. It is the chief iron-storage protein in the body.
   2. It represents stored iron.
2. Indications:
   1. It diagnoses iron deficiency or excess.
   2. It predicts and monitors iron deficiency.
   3. It tells the response to iron therapy.
   4. It differentiates iron deficiency from chronic diseases as a cause of anemia.
   5. It monitors iron status in patients with chronic renal diseases with or without dialysis.
   6. It can be used as a population study for iron levels and response to the iron supplement.
3. Ferritin interpretations:
4. 10% to 20% to 30% of the total iron is stored as Ferritin.
5. Iron is stored as ferritin in the body in the liver, spleen, and bone marrow.
6. Or stored as Ferric (Fe ⁺⁺⁺) bound to an apoferritin protein molecule.
7. When iron is needed, it is released from the Ferritin and bound to the β₁ globulin molecule, transferrin.
8. Serum Ferritin is the best diagnostic test for iron deficiency anemia.
9. Because ferritin is the measure of the iron stored in the body.
10. In iron deficiency anemia, the ferritin level is <15 µg/L as compared to the normal level of 20 to 250 µg/L.
    1. In children <, 6 µg/L  compared to the normal value of 7 to140 µg/L.
    2. In baby <, 12 µg/L compared to the normal values of 50 to 200 µg/L.
11. Ferritin is the acute phase protein, so its value may increase in infections, SLE, liver diseases, malignancies, and chronic renal failure.

Transferrin

1. Definition of transferrin:
   1. Transferrin transport circulating Fe⁺⁺⁺ molecule.
   2. Normally there are only 1/3 sites of iron bindings are occupied.
   3. The remaining unoccupied sites are called unsaturated iron-binding capacity.
2. Indications:
   1. It differentiates different types of anemia.
3. Transferrin interpretations:
4. It represents the major protein that binds to iron. The majority of the iron is bound to transferrin.
5. Transferrin is a beta-globulin (β1-globulin).
6. Transferrin’s capacity to bind iron in normal plasma is 240 to 360 µg/dL.
7. Transferrin also acts as an acute-phase protein.
8. This is a transport protein synthesized in the liver.
9. This regulates iron absorption.
10. Transferrin is also called siderophilin.
    1. Total iron + TIBC + Transferrin, when done together, helps in the differential diagnosis of anemia.
11. The cellular uptake of iron is mediated by the cell surface transferrin receptor (TR).
    1. The number of transferrin receptors depends upon the needs of the cell for iron.
    2. In the case of apoferritin deficiency, an excess of the iron is deposited as small granules as Iron-oxide, called hemosiderin.

Transferrin saturation

1. Definition of transferrin saturation:
   1. Serum transferrin saturation is derived by dividing total serum iron/ TIBC.
2. Indications:
   1. It differentiates the diagnosis of anemia.
   2. Hereditary hemochromatosis differentiation.
3. Transferrin saturation interpretations:
4. It is the percentage of transferrin and other iron-binding proteins.
5. Transferrin saturation is calculated as follows.
   1. Transferrin saturation (%) = serum iron level (µg/dL) / TIBC (µg/dL) x 100
      1. The normal value for transferrin saturation is 20 to 50%.
      2. This may vary with age and sex.
   2. Transferrin saturation is helpful in finding the cause of abnormal iron and TIBC levels.
   3. Transferrin saturation is decreased below 15% in a patient with iron deficiency anemia.
   4. Transferrin saturation is increased in patients:
      1. Hemolytic anemia.
      2. Sideroblastic anemia.
      3. Megaloblastic anemia.
      4. Patient with iron overload or iron poisoning.
      5. Hemochromatosis.

Total iron-binding capacity (TIBC)

1. It is the capacity of transferrin to bind to iron.
2. TIBC is an indirect measurement of Transferrin concentration.
   1. TIBC measures the total amount of iron that apotransferrin has the capacity to bind.
3. TIBC refers to the amount of iron that could be bound by saturation of transferrin and other minor iron-binding proteins present in the serum or plasma.
4. TIBC is the sum of all protein-bound to iron.
5. TIBC increases by 70% in patients with iron deficiency anemia.
6. When serum iron falls, then TIBC increases.
7. TIBC is increased in the presence of iron deficiency but may be normal or low in chronic diseases.
8. TIBC may be calculated from the direct measurement of serum transferrin by the following formula:
   1. TIBC µg/dL = serum transferrin mg/dL x 1.25²¹ ( Another reference = Transferrin mg/dL x 0.025).
   2. A small proportion of the iron is bound to other proteins, so the above equation underestimates the TIBC.
9. The unsaturated iron-binding capacity, the amount of apotransferrin that is still available to bind the iron, can be measured.
   1. It is measured as = TIBC minus serum iron (µg/dL)

Normal TIBC, Transferrin, and Transferrin saturation

Source 1

Transferrin

• To convert into SI units x 0.01 = g/L

Total Iron binding capacity (TIBC)

• Adult = 250 to 425 µg/dL

Iron saturation (%Transferrin saturation)

• Male = 20 to 50%
• Female = 15 to 50%
  • To convert into SI units x 0.01 = Fraction saturation

Source 2

TIBC 

1. 250 to 400 µg/dL.
2. It decreases in older people at around = 250 µg/dL.
   • (This value varies from one reference to another)

Transferrin

1. Adult = 250 to 425 mg/dL.
2. Children = 203 to 360 mg/dL.
3. Newborn = 130 to 275 mg /dL.

Transferrin saturation

1. Male = 20 to 50 %.
2. Female = 15 to 50 %.

Ferritin 

1. Adult male = 12 to 300 ng/mL (12 to 300 µg/L).
2. Adult female = 10 to 150 ng/mL (10 to 150  µg/L).
3. Children
   1. Newborn = 25 to 200 ng/mL.
   2. One-month-old = 200 to 600 ng/mL.
   3. 2 to 5 months old = 50 to 200 ng/mL.
   4. 6 months = 7 to 142 ng/mL.

Decreased Ferritin level:

• Iron-deficiency anemia.

Increased Ferritin level:

1. Ferritin is an acute-phase protein raised in chronic liver diseases, alcoholism, malignancies, infection, and inflammation.
2. In hemosiderosis.
3. In idiopathic hemochromatosis.
4. Anemias other than iron deficiency.
5. Renal cell carcinoma due to hemorrhage in the tumor.
6. End-stage renal diseases.
7. It increases with age.

Increased TIBC is seen in the following:

1. Pregnancy.
2. Iron deficiency.
3. Acute hepatitis.
4. Acute and chronic blood loss.

The decreased TIBC is seen in the following:

1. Hemochromatosis.
2. Hypoproteinemia in malabsorption.
3. Burns.
4. Cirrhosis.
5. Renal diseases like nephrosis etc.
6. Thalassemia.
7. Hyperthyroidism.
8. Chronic diseases.
9. Non-iron deficiency anemia

The increased Transferrin is seen in:

1. Iron deficiency anemia.
2. Pregnancy.
3. Estrogen therapy.
4. Hyperestrogenism.

The decreased Transferrin is seen in:

1. Chronic infections.
2. Acute inflammation.
3. Microcytic anemia due to chronic diseases.
4. Protein deficiency in malabsorption and burns.
5. Liver disease, acute.
6. Renal disease like nephrosis.
7. Hemochromatosis.
8. Genetic deficiency of transferrin.

Transferrin saturation increased:

1. Hemochromatosis.
2. Thalassemia.
3. Hemosiderosis.
4. Ingestion of iron.
5. Birth control pills.
6. Iron dextran injection.

Transferrin saturation decreased:

1. Iron deficiency anemia.
2. Anemia of infections and chronic diseases.
3. Uremia.
4. In some of the malignancies.
5. Rheumatoid arthritis.

Differential diagnosis of various diseases:

Questions and answers:

• Please see more details in Total Iron.