Q. I am having trouble differentiating between mild thalassemia and iron-deficiency anemia. I am not sure why the red cell distribution width would be lower in thalassemia than IDA. Could you please explain this and list other ways to tell them apart?

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 cells (as you can see in the image of iron-deficiency anemia above). The 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.


23 Responses to How can you differentiate between iron-deficiency anemia and thalassemia?

  1. MZaheen says:

    Hello guys..
    I got a simple calculation based just on CBC (Complete Blood Count)

    DF = (MCV)2 x RDW – CV / Hb. x 100

    Where- DF= Discriminent Function
    (MCV, RDW, Haemoglobin are CBC based values)

    Thus if DF value 70 Suspect for IDA

  2. medshamsstudent says:


  3. mariam says:


  4. sufia says:

    To separate thalassemia trait and IDA
    1.Hb in TT is not less than 10g/dl but in IDA it is less upto 3g/dl.
    2.RBC is more than 5million but in IDA it is less.
    3.RDW is less than 17% in TT but in IDA it is more than 17%.

  5. matthew says:

    not forgetting the mentzer index as well — ratio of MCV and RBC – if more than 13 then its likely IDA. if less than 13 its suggestive of thal.

  6. admin says:

    Yes – good point! As you suggest in your comment, this test is not a definitive test (it’s pretty specific but not all that sensitive).

  7. Govindarajan says:

    how can we differentiate target cell is due to liver disease or thalassemia?

  8. Kristine says:

    You’d have to look at the whole smear, the CBC (specifically, the MCV, RBC and RDW), and the patient’s clinical status.

    In uncomplicated liver disease (in which there is no iron-deficiency anemia due to bleeding, and no folate deficiency), the anemia is macrocytic, and there may be acanthocytes.

    More often, though, there are complications in patients with liver disease: bleeding (leading to iron deficiency and a microcytic anemia) or nutritional abnormalities like folate deficiency (leading to a megaloblastic anemia). The anemia may even be a mixture of all of these features!

    Mild thalassemia is microcytic, with a normal or elevated RBC and very mild anisocytosis. Severe thalassemia is also microytic, but the RBC is low and there is a ton of anisocytosis.

    So: there are a lot of different features to be aware of. You may need to do look at the patient’s other labs (liver function tests, etc) and/or do hemoglobin electrophoresis to figure things out.

    Hope that helps.

  9. dear sir/mam;

    thank you for the very informative haematology topic…as a Biomedical Scientist…with this additional reinforcement of info as knowledge application it will help me more validate correct clinical lab results for final analysis and lab diagnosis therefore exact prescription and patient`s medication…:::


  10. kanmani says:

    Thanks a LOT!!!!!!!!!!

  11. Dr Ganesh says:

    To differentiate anemia and Thalassemia-
    1. You get mark anisopoikilocytosis in anemia and
    2. The Mentzer index which is defined as mean corpuscular volume per red cell count. An index of less than 13 suggests that the patient has the thalassemia trait, and an index of more than 13 suggests that the patient has iron deficiency.

  12. dr. Poonam ATAL Khambra says:

    reason for the RBC count to be normal or elevated is because defect lies at globin chain formation level but no nutritional deficiency otherwise .so process of formation of red cells remains normal or slightly elevated to compensate for early disposal of RBCs.and ps definately helps to differentiate between the two and indices also.

  13. z says:

    very good!

  14. Sahan says:


  15. Ehsan says:

    Thank you so much.

  16. Sepehr says:

    Very helpful , Thanks every1

  17. Ahmed says:

    helped me a lot; thank u so much.

  18. mosi says:

    RBC=5.15 HB=13.7 Hct=40.8 MCV=79.3 MCH=26.6

    MCHC=33.4 RDW=14.2 WBC=4.9

    can you help me? iron-deficiency anemia or

  19. Kristine says:

    Probably thalassemia, given the low MCV and normal hemoglobin – but you’d need to do iron studies to be sure 🙂

  20. […] the way, the place that the RDW is most useful (in my humble opinion) is in differentiating between iron-deficiency anemia (IDA) and mild to moderate thalassemia. In IDA, as we just talked about, the RDW is high. In mild-moderate thalassemia, the RDW is not […]

  21. geeta lallmahomed says:

    Thank you very much for your help….it makes things at the lab

  22. dr shaheen says:

    thanks every one very informative discussion

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