Reason to perform an iron panel test:
These tests are used to evaluate iron metabolism in patients when iron deficiency, overload, or poisoning is suspected.
Let’s look closer at the test:
Abnormal levels of iron are characteristic of many diseases, including iron-deficiency anemia and hemochromatosis (=Iron overload).
As much as 70% of the iron in the body is found in the hemoglobin of the red blood cells (RBCs). The other 30% is stored in the form of ferritin and hemosiderin (=iron-storage complex within cells, not widely available).
Iron is supplied by the diet. About 10% of the ingested iron is absorbed in the small intestine and transported to the plasma. There the iron is bound to a globulin protein called transferrin and carried to the bone marrow for incorporation into hemoglobin.
Transferrin exists in relationship to the need for iron. When iron stores are low, transferrin levels increase, whereas transferrin is low when there is too much iron.
Usually about one-third of the transferrin is being used to transport iron.
Because of this, the blood serum has considerable extra iron-binding capacity, which is the Unsaturated Iron Binding Capacity (UIBC). The TIBC equals UIBC plus the serum iron measurement. Some laboratories measure UIBC, some measure TIBC, and some measure transferrin. The serum iron determination is a measurement of the quantity of iron bound to transferrin.
What is anemia?
Iron-deficiency anemia is a result of reduced stored iron. It has many causes, including:
- (1) insufficient iron intake,
- (2) inadequate gut absorption,
- (3) increased requirements (as in growing children and late pregnancy), and
- (4) loss of blood (as in menstruation, bleeding peptic ulcer, colon neoplasm).
Iron deficiency results in a decreased production of hemoglobin, which in turn results in a small, pale (microcytic, hypochromic) red blood cell.
A decrease in the mean corpuscular volume and mean corpuscular hemoglobin concentration is also seen.
A decreased serum iron level, elevated total iron-binding capacity (TIBC), and low transferrin saturation value are characteristic of iron-deficiency anemia.
Acute iron poisoning due to accidental or intentional overdose is characterized by a serum iron level that exceeds the total iron binding capacity (TIBC).
What is iron overload?
Chronic iron overload or poisoning is called hemochromatosis or hemosiderosis. Excess iron is usually deposited in the brain, liver, and heart and causes severe dysfunction of these organs.
Massive blood transfusions also may cause elevated serum iron levels, although only transiently. Transfusions should be avoided before serum iron level determinations.
TIBC is a measurement of all proteins available for binding mobile iron. Transferrin represents the largest quantity of iron-binding proteins. Therefore TIBC is an indirect yet accurate measurement of transferrin.
Ferritin is not included in TIBC, because it binds only stored iron.
During iron overload, transferrin levels stay about the same or decrease, whereas the other less common iron-carrying proteins increase in number. In this situation, TIBC is less reflective of true transferrin levels. TIBC is increased in 70% of patients with iron deficiency. Transferrin is a negative acute-phase reactant protein. That is, in various acute inflammatory reactions, transferrin levels diminish.
Transferrin and chronic illness
Transferrin also is diminished in patients with chronic illnesses such as malignancy, collagen-vascular diseases, or liver diseases. Hypoproteinemia is also associated with reduced transferrin levels. Pregnancy and estrogen therapy are associated with increased transferrin levels. TIBC varies minimally with iron intake. TIBC is more a reflection of liver function (transferrin is produced by the liver) and nutrition than of iron metabolism. TIBC values often are used to monitor the course of patients receiving hyperalimentation.
TIBC and Transferrin Saturation
The percentage of transferrin and other mobile iron-binding proteins saturated with iron is calculated by dividing the serum iron level by the TIBC.
Transferrin saturation(%) = Serum iron level × 100% / TIBC
The normal value for transferrin saturation is 20% to 50%. Calculation of transferrin saturation is helpful in determining the cause of abnormal iron and TIBC levels. Transferrin saturation is decreased to below 15% in patients with iron deficiency anemia. It is increased in patients with hemolytic, sideroblastic, or megaloblastic anemias and also in patients with iron overload or iron poisoning.
Increased intake or absorption of iron (as in hemochromatosis) leads to elevated iron levels. In such cases the TIBC is unchanged; as a result, the percentage of transferrin saturation is very high.
Unsaturated iron binding capacity (UIBC) has been proposed as an inexpensive alternative to transferrin saturation. Chronic illness (eg, infections, neoplasia, cirrhosis) is characterized by a low serum iron level, decreased TIBC, and normal transferrin saturation. Pregnancy is marked by high levels of protein, including transferrin. Because iron requirements are high, it is not unusual to find low serum iron levels, high TIBC, and a low percentage of transferrin saturation in late pregnancy.
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