Total Iron Binding Capacity (TIBC), Transferrin and Transferrin Saturation

Sample

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

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

Purpose of the test (Indications)

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

Pathophysiology

Iron

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

1. 4. Iron in the food is absorbed by the intestinal epithelium.
   5. Iron is ingested as Fe ⁺⁺⁺ form and is converted to Fe ⁺⁺ form for the absorption.
   6. The conversion of Fe ⁺⁺⁺ to Fe ⁺⁺ form takes place in the stomach where gastric acid HCL provides the acidity to reduce the iron.

1. 7. Ferric (Fe⁺⁺⁺) iron is reduced to Ferrous (Fe⁺⁺) by vit.C and this ferrous form is absorbed very easily.
   8. Milk and antacid bind to iron and reduce its absorption.
      6. Iron 1 mg/day is lost in the urine, sweat, bile, and epithelial cells.

1. 9. In the blood, this absorbed iron attaches with the transport protein (Transferrin).
   10. So transferrin may indirectly represent the TIBC.

Ferritin represents stored iron.

1. 1. 10 to 20% to 30% of the total iron is stored as Ferritin.
   2. Iron is stored as ferritin in the body in the liver, spleen, and bone marrow.
   3. Or stored as Ferric (Fe ⁺⁺⁺) bound to an apoferritin protein molecule.
   4. When iron is needed then it is released from the Ferritin and is then bound to the β₁ globulin molecule, transferrin.
   5. Serum Ferritin is the best diagnostic test for iron deficiency anemia.
      1. Because ferritin is the measure of the iron stores in the body.
      2. In an 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.
   6. Ferritin is the acute phase protein, so its value may increase in infections, SLE, liver diseases, malignancies, and chronic renal failure.

Transferrin represents the major protein that binds to iron. The majority of the iron is bound to transferrin.

1. 1. Transferrin is a beta-globulin (β1-globulin).
   2. Transferrin capacity to bind iron in normal plasma is 240 to 360 µg/dL.
   3. Transferrin also acts as an acute-phase protein.
   4. This is a transport protein synthesized in the liver.
   5. This regulates iron absorption.
   6. Transferrin also called siderophilin.
      • Total iron + TIBC + Transferrin when done together helps in the differential diagnosis of anemia.
   7. 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 the 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 is the percentage of transferrin and other iron-binding proteins.

1. 1. 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 to find 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) is the capacity of transferrin to bind to iron.

1. 1. TIBC is an indirect measurement of Transferrin concentration.
      1. TIBC measures the total amount of iron that apotransferrin has the capacity to bind.
   2. 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.
   3. TIBC is the sum of all protein-bound to iron.
   4. TIBC increases by 70% of the patients with iron deficiency anemia.
   5. When serum iron falls then TIBC increases.
   6. TIBC is increased in the presence of iron deficiency but may be normal or low in chronic diseases.
      1. 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.
         2. A small proportion of the iron is bound to other proteins, so the above equation underestimates the TIBC.
      2. The unsaturated iron-binding capacity, the amount of apotransferrin is still available to bind the iron, can be measured.

Normal

Source 1

Transferrin

Age	mg/dL
0 to 4 days	130 to 275
3 months to 16 years	203 to 360
16 to 60 years
Male	215 to 365
Female	250 to 380
60 to 90 years	190 to 375
>90 years	186 to 347
Maternal at term	305

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

Transferrin

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

Transferrin saturation

1. 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.

Increased TIBC is seen in:

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

The decreased TIBC is seen in:

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

The decreased Transferrin is seen in:

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

Disease	Total Iron	TIBC	Transferrin saturation
Hemochromatosis	Raised	unchanged	Very high
Chronic illness	Low	Decreased or Normal
Pregnancy	Low	High	Low

• Please see more details in Total Iron.

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