A young girl presents with history of fatigability and weakness. Hb was 6.5, MCV 70, MCH 22. RDW 16. Diagnosis is. (AIPG 2010)
|A||Iron deficiency anemia|
|B|| Thalassemia minor |
|D||Sickle cell trait|
Iron deficiency anemia
(Extra Edge: Hari-18th ed., Pg. 846)
Blood loss in excess of 10–20 mL of red cells per day is greater than the amount of iron that the gut can absorb from a normal diet.
Under these circumstances the iron deficit must be made up by mobilization of iron from RE storage sites. During this period, iron stores—reflected by the serum ferritin level or the appearance of stainable iron on bone marrow aspirations—decrease.
As long as iron stores are present and can be mobilized, the serum iron, total iron-binding capacity (TIBC), and red cell protoporphyrin levels remain within normal limits. At this stage, red cell morphology and indices are normal.
By definition, marrow iron stores are absent when the serum ferritin level is <15 g/L. As long as the serum iron remains within the normal range, hemoglobin synthesis is unaffected despite the dwindling iron stores.
Once the transferrin saturation falls to 15–20%, hemoglobin synthesis becomes impaired. This is a period of iron-deficient erythropoiesis.
In the peripheral blood smear the first appearance of microcytic cells.
Gradually, the hemoglobin and hematocrit begin to fall, reflecting iron-deficiency anemia. The transferrin saturation at this point is 10–15%.
Serum Iron and Total Iron-Binding Capacity
1. The serum iron level represents the amount of circulating iron bound to transferrin. The TIBC is an indirect measure of the circulating transferrin.
2. The normal range for the serum iron is 50–150 g/dL; the normal range for TIBC is 300–360 g/dL. Transferrin saturation, which is normally 25–50%, is obtained by the following formula: serum iron x 100 ÷ TIBC.
3. Iron-deficiency states are associated with saturation levels below 20%.
4. A transferrin saturation >50% indicates that a disproportionate amount of the iron bound to transferrin is being delivered to non erythroid tissues. If this persists for an extended time, tissue iron overload may occur.
5. As iron stores are depleted, the serum ferritin falls to <15 g/L are diagnostic of absent body iron stores.
Red Cell Protoporphyrin Levels
1. Protoporphyrin is an intermediate in the pathway to heme synthesis. Under conditions in which heme synthesis is impaired, protoporphyrin accumulates within the red cell.
2. This reflects an inadequate iron supply to erythroid precursors to support hemoglobin synthesis. Normal values are <30 g/dL of red cells. In iron deficiency, values in excess of 100 g/dL are seen.
3. The most common causes of increased red cell protoporphyrin levels are absolute or relative iron deficiency and lead poisoning.
Serum Levels of Transferrin Receptor Protein:
1. Because erythroid cells have the highest numbers of transferrin receptors of any cell in the body, and because transferrin receptor protein (TRP) is released by cells into the circulation, serum levels of TRP reflect the total erythroid marrow mass.
2. Another condition in which TRP levels are elevated is absolute iron deficiency. Normal values are 4–9 g/L determined by immunoassay.
3. This laboratory test is along with the serum ferritin, is used to distinguish between iron deficiency and the anemia of chronic inflammation.
Changes in lab values in iron deficiency anemia
1. Ferritin, 2. Hb, 3. MCV
1. TIBC, 2. Serum transferrin, iii. RDW
Comparison of IDA & Thalassemia anemia
1. Iron deficient anemia and thalassemia minor present with many of the same lab results. It is very important not to treat a patient with thalassemia with an iron supplement as this can lead to hemochromatosis (accumulation of iron in various organs especially liver).
2. Hb electrophoresis provides useful evidence in distinguishing these two conditions, along with iron studies
1. Bone marrow iron is decreased earlier than serum iron.
2. As long as iron stores are present (serum ferritin, bone marrow iron), and can be mobilized,
3. The serum iron, TIBC and RBC protoporphyrin levels remains within normal limits.