Clearly, as iron deficiency develops, it will go through various stages, each with its own pattern.
1. IN THE EARLIEST STAGE, iron is gradually being lost from the stores. The serum iron studies are still normal, the FBC appearance is normal. This is called LATENT IRON DEFICIENCY, and there is no specific clinical or laboratory feature to suspect it. It is only if a bone marrow aspirate were done – and clearly there would not normally be any indication for doing it – that one would see that stainable iron and sideroblasts are reduced, and ultimately absent. If one were really suspicious about the possibility of latent iron deficiency, one would still need considerable justification for submitting a patient to aspiration. However, red cell protoporphyrin levels (increased) are an acceptable substitute. Transferrin receptor levels are raised, and the RDW at this stage is still normal. As indicated above, this stage can last for a very variable time, depending on the balance between
a) The rate of blood loss and
b) The amount of dietary iron (and in what form), the efficacy of absorption, and the quality of the bone marrow
2. Once IRON STORES ARE DEPLETED, the following changes are seen:
a) Serum iron decreases steadily.
b) Transferrin increases steadily.
c) % Saturation falls steadily.
d) Stainable iron and sideroblasts are absent from the marrow.
e) The RDW rises.
f) A right shift of the neutrophils gradually develops.
3. It is only now that IRON DEFICIENCY AS SUCH is established:
a) The % saturation is well below 15.
b) The red cells become microcytic.
c) The red cells start off by showing anisochromia then full-fledged hypochromia.
d) The RDW tends to diminish.
e) Plus the other changes as mentioned before.
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