How to differentiate between Haemolytic anaemia, Thalassemia and Iron deficiency anaemia?

A. As iron-deficiency anemia progresses, and the patient’s serum iron drops lower and lower, each successive wave of new red cells gets smaller and smaller. So there are some kind of small cells, and some really small cellsThe red cell distribution width (RDW) is high in iron deficiency anemia because there is a wide variation in red cell size. In mild thalassemia (alpha or beta), the red cells are strangely all the same size; there is virtually no variation. So the RDW is low. This difference in RDW is helpful when you’re trying to differentiate IDA and thalassemia; if you have a microcytic, hypochromic anemia, the next thing you’d do is look at the RDW (or just look at the blood smear). If the RDW is low (the cells are mostly the same size), then it’s probably thalassemia. If the RDW is high (the cells vary a lot in size), then it’s probably iron deficiency anemia.

Another thing to do is look at the RBC. In IDA, the RBC is low (there isn’t enough iron around, so the bone marrow makes fewer cells). In mild thalassemia, however, the RBC tends to be normal or even elevated. The reasons for this are unclear.

To definitively diagnose IDA, you need to do iron studies; to definitively diagnose thalassemia, you need to do hemoglobin electrophoresis. But you can get a pretty good idea by looking at the things discussed above.

Although both iron deficiency anaemia and thalassaemia minor show microcytic and hypochromic red cells, presence of target cells, polychromatic cells, and basophilic stippling on blood smear suggest the diagnosis of thalassaemia minor.

Red cell count is normal or raised in thalassaemia minor while it is reduced in iron deficiency anaemia. In thalassaemia, although red cell abnormalities are prominent anaemia is mild or absent. In iron deficiency anaemia, red cell changes correlate with severity of anaemia.

MCV and MCH are markedly reduced as compared to the degree of anaemia in thalassaemia minor.

A typical feature of thalassaemia minor on haemoglobin electrophoresis is increased proportion of HbA2 (>3.5%).

Bone marrow examination for iron stores also distinguishes the two conditions.  

Differentiation of iron deficiency anaemia from thalassaemia minor is important as continued iron therapy in the latter condition can cause iron overload.