IRON METABOLISM

Table of Contents

IRON METABOLISM AND TESTING: Serum Iron, TIBC And Ferritin


IRON


Iron, an essential trace element, primarily binds to proteins within the body. It associates with haem, found in haemoglobin, myoglobin, cytochromes, as well as non-haem proteins like ferritin, transferrin, flavoproteins, and oxygenases. On average, adult males possess around 4 grams of body iron, while females have approximately 3 grams due to lower reserves and relatively lower haemoglobin concentration.

Iron Distribution and Storage

About 70% of total iron resides in haemoglobin and myoglobin, while the remaining 30% is stored within the reticuloendothelial system, primarily in the liver, bone marrow, and spleen in the form of ferritin and haemosiderin aggregates.

Iron Transport and Excretion:

Iron is transported via transferrin, a globulin. There’s no direct physiological mechanism for iron excretion; instead, the body regulates iron stores by controlling absorption. Daily, approximately 1 mg of iron is lost due to normal shedding of cells and erythrocytes in urine and feces. Hence, men require about 1 mg of iron per day, while women need 1.5-2.0 mg. Lactating and pregnant women may need around 3 mg.

Factors Affecting Iron Absorption:

  • Source of Iron: Haem iron from dietary sources like haemoglobin and myoglobin is more efficiently absorbed than non-haem iron.
  • Gastric Factors: Hydrochloric acid in gastric secretions converts ferric iron to the absorbable ferrous form.
  • Enhancers and Inhibitors: Ascorbic acid, sugars, and amino acids aid absorption, while substances like oxalates, phytates, and tannates inhibit it.
  • Physiological Conditions: Anemia, increased erythropoiesis, and intestinal motility influence iron absorption.

Serum Iron Measurement:

Measuring serum iron is limited in understanding iron metabolism except in specific conditions like haemochromatosis and managing iron poisoning. Fluctuations occur due to various physiological factors such as sex, circadian rhythm, and menstrual cycle.

Serum Iron Determination Process

Serum iron is released from transferrin iron complexes, reduced to ferrous form, and reacts with chromogens to produce color intensity proportional to iron concentration.

Reference Ranges:

  • Male: 50-160 μg/dl
  • Female: 40-150 μg/dl

TOTAL IRON BINDING CAPACITY (TIBC)


Definition:

Total Iron Binding Capacity (TIBC) is a blood test that measures the maximum amount of iron that can be bound by proteins in the blood, particularly transferrin. Transferrin is a key protein responsible for transporting iron throughout the bloodstream and regulating iron levels in the body.

Purpose:

The TIBC test is utilized in conjunction with other iron-related tests to assess the body’s iron status. By measuring TIBC along with serum iron and transferrin saturation, healthcare providers can evaluate how effectively the body transports and utilizes iron.

Measurement:

TIBC values are typically reported in micrograms of iron per deciliter of blood (mcg/dL). A higher TIBC value may suggest a greater capacity for binding iron, indicating a compensatory response to lower-than-normal iron levels. Conversely, a lower TIBC value may indicate that the body’s iron stores are sufficient, and less transferrin is available to bind additional iron.

Clinical Significance:

TIBC alone does not provide a complete assessment of iron status; it is interpreted alongside other iron-related tests and the patient’s clinical history. Abnormal TIBC levels can be associated with conditions such as iron deficiency anemia, hemochromatosis (iron overload), or chronic diseases.

Interpretation:

Healthcare professionals interpret TIBC results within the context of the overall clinical picture to make an accurate diagnosis. Abnormal TIBC levels can prompt further investigation and may guide appropriate interventions to address iron-related disorders.

Conclusion:

Total Iron Binding Capacity is a valuable tool in assessing iron status, aiding healthcare providers in understanding how the body manages iron. Interpretation of TIBC results should be done in consultation with a healthcare professional to ensure comprehensive and accurate clinical decision-making.

Reference Ranges:

Adults: 45-75 μmol/L


FERRITIN


Definition:

Ferritin is a protein that stores iron and releases it in a controlled manner according to the body’s needs. It plays a crucial role in iron homeostasis, serving as the primary intracellular storage for iron in various tissues, especially the liver, spleen, and bone marrow.

Measurement:

Ferritin levels are commonly measured through a blood test and are expressed in nanograms per milliliter (ng/mL) of blood. The test provides insight into the amount of iron stored in the body.

Function:

Ferritin acts as a reservoir for iron, releasing it when the body requires additional iron for functions such as the production of red blood cells. Monitoring ferritin levels helps assess the adequacy of iron stores and is valuable in diagnosing conditions related to iron deficiency or overload.

Clinical Significance:

  • Iron Deficiency: Low ferritin levels often indicate iron deficiency, which can lead to conditions like iron-deficiency anemia.
  • Iron Overload: Elevated ferritin levels may be associated with iron overload disorders, such as hemochromatosis, where the body absorbs and stores too much iron.

Interpretation:

Healthcare providers consider ferritin levels alongside other iron-related tests to determine the underlying cause of abnormal iron status. Low ferritin levels may prompt investigation into the reasons for iron deficiency, while high levels may necessitate further evaluation for iron overload disorders.

Diagnostic Importance:

Ferritin is a key biomarker used in diagnosing and monitoring iron-related disorders. It aids in tailoring appropriate interventions, such as iron supplementation or therapeutic phlebotomy, depending on whether there is a deficiency or excess of iron.

Conclusion:

Ferritin is a vital indicator of iron stores in the body, offering valuable information about iron status. Interpretation of ferritin levels should be done in consultation with a healthcare professional to guide proper diagnosis and management of iron-related conditions.

Reference Ranges:

  • Adult male: 20-300 μg/L
  • Adult female: 15-120 μg/L
  • Children: 10-140 μg/L
  • Newborn/Infant: 25-200 μg/L

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