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  Back Blood-tests Explained


Transferrin


At a Glance

Why Get Tested?

To assess your body's ability to transport iron in the blood

When to Get Tested?

When your doctor suspects you may have too much or too little iron in your body because of a variety of conditions; to help monitor liver function and nutrition

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

You may be instructed to fast for 12 hours before the test; in this case, only water is allowed.

The Test Sample

What is being tested?

Transferrin is the main protein in the blood that binds to iron and transports it throughout the body. The amount of transferrin that is available to bind to and transport iron is reflected in measurements of the total iron binding capacity (TIBC), unsaturated iron binding capacity (UIBC), or transferrin saturation.

Normally, iron is absorbed from food and transported throughout the body by transferrin, which is produced by the liver. About 70% of the iron is transported to the bone marrow and incorporated into the production of hemoglobin within red blood cells. The remainder is stored in the tissues as ferritin or hemosiderin. The amount of transferrin in the blood depends upon liver function and a person's nutritional status. Under normal conditions, its binding sites are typically one-third saturated with iron. This means that two-thirds of its capacity is held in reserve.

The transferrin test, TIBC, UIBC, and transferrin saturation evaluate the blood's ability to bind and transport iron and are a reflection of iron stores.

  • The TIBC measures the total amount of iron that can be bound by proteins in the blood. Since transferrin is the primary iron-binding protein, the TIBC test is a good indirect measurement of transferrin availability.
  • The UIBC test determines the reserve capacity of transferrin, i.e., the portion of transferrin that has not yet been saturated with iron. UIBC can be measured directly or calculated as TIBC – iron = UIBC.
  • Serum iron measures the total amount of iron in the blood, nearly all of which is bound to transferrin. It is required to calculate either the TIBC or UIBC.
  • Transferrin saturation is a calculation (see Common Questions #2) using the iron test result and the TIBC or UIBC results, representing the percentage of the transferrin that is saturated with iron.

 

How is the sample collected for testing?

A blood sample is drawn by needle from a vein in the arm.

Is any test preparation needed to ensure the quality of the sample?

A 12-hour fast may be required. In this case, only water is allowed. A morning specimen is preferred.

The Test

How is it used?

Total iron-binding capacity (TIBC) is most frequently used along with a serum iron test to evaluate people suspected of having either iron deficiency or iron overload. These two tests are used to calculate the transferrin saturation, a more useful indicator of iron status than just iron or TIBC alone. In healthy people, about 20-40% of available transferrin sites are used to transport iron.

In iron deficiency, the iron level is low but the TIBC is increased, thus transferrin saturation becomes very low. In iron overload states, such as hemochromatosis, the iron level will be high and the TIBC will be low or normal, causing the transferrin saturation to increase. UIBC may be ordered as an alternative to TIBC.

It is customary to test for transferrin (instead of TIBC or UIBC) when evaluating a person's nutritional status or liver function. Because it is made in the liver, transferrin will be low in those with liver disease. Transferrin levels also drop when there is not enough protein in the diet, so this test can be used to monitor nutrition.

When is it ordered?

TIBC or UIBC may be ordered along with serum iron when it appears that a person has iron deficiency or overload. One or more tests may be ordered when there are signs of anemia, especially when a CBC is performed and shows red blood cells that are microcytic and hypochromic and the hemoglobin and hematocrit levels are low.

The most common symptoms of anemia include:

  • Chronic fatigue/tiredness
  • Dizziness
  • Weakness
  • Headaches
  • Pale skin (pallor)

When a doctor suspects that a person may have iron overload or when a person has a family history of hemochromatosis, iron and TIBC may be ordered along with a ferritin test. Symptoms of iron overload will vary from person to person and tend to worsen over time. They are due to iron accumulation in the blood and tissues. Symptoms may include:

  • Joint pain
  • Fatigue, weakness
  • Weight loss
  • Lack of energy
  • Abdominal pain
  • Loss of sex drive
  • Loss of hair
  • Heart problems, such as congestive heart failure (CHF)

However, many people have no initial symptoms.

Iron and TIBC are also ordered when there is a case of suspected iron poisoning. This is most common in children who accidentally overdose with vitamins or other supplements containing iron.

A transferrin test may be ordered along with other tests such as prealbumin when a doctor wants to evaluate or monitor a person's nutritional status.

What does the test result mean?

The results of transferrin tests, TIBC, or UIBC are usually evaluated in conjunction with other iron tests. A summary of the changes in iron tests seen in various diseases of iron status is shown in the table below.

Disease Iron TIBC/Transferrin UIBC

%Transferrin

Saturation

 Ferritin
Iron Deficiency Low High High Low Low
Hemochromatosis High Low Low High High
Chronic Illness Low Low Low/Normal Low Normal/High
Hemolytic Anemia High Normal/Low Low/Normal High High
Sideroblastic Anemia Normal/High Normal/Low Low/Normal High High
Iron Poisoning High Normal Low High Normal

A high TIBC, UIBC, or transferrin usually indicates iron deficiency, but they are also increased in pregnancy and with the use of oral contraceptives.

A low TIBC, UIBC, or transferrin may occur if someone has:

  • Hemochromatosis
  • Certain types of anemia due to accumulated iron
  • Malnutrition
  • Inflammation
  • Liver disease
  • Nephrotic syndrome, a kidney disease that causes a loss of protein in urine

Transferrin saturation is decreased with iron deficiency and increased when excess amounts of iron are present, as in iron overload or poisoning.

Is there anything else I should know?

Recent blood transfusions can affect test results. Multiple blood transfusions can sometimes lead to iron overload.



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