A haemoglobin of 9.4 arrives, and an iron tablet is started the same day. For a great many people that is exactly the right sequence. For a substantial minority it is the wrong treatment for the wrong reason, taken for months before anybody looks again.
Anaemia is not a disease. It is the visible end of at least a dozen different processes, and the useful question is never "how low is it" but "why is it low".
Ferritin, and the trap inside it
Ferritin measures stored iron and is the single most useful test for the commonest cause of anaemia in India. Below 15 micrograms per litre in an adult, the stores are empty. Between 15 and about 30 they are usually still inadequate, particularly in someone with symptoms, and recent work suggests the body starts rationing iron for red cell production at higher levels than the old cut-offs assumed.
The trap is that ferritin is also an acute-phase protein. It rises with infection, inflammation, liver disease, obesity and recent illness, entirely independently of how much iron you have. So a normal or high ferritin does not by itself rule out deficiency in someone who is unwell.
This is why a CRP is often reported beside a ferritin, and why an iron study is read as a set. Ferritin alone, measured during a fever, can say the opposite of the truth.
When ferritin is ambiguous, transferrin saturation helps: it is serum iron expressed against total iron binding capacity, and a figure under about 16 per cent points towards deficient supply reaching the marrow.
Two practical notes on iron studies. Serum iron on its own is a poor test, because it swings widely through the day. And it rises for a day or two after an iron tablet, so a study done while you are taking iron can read reassuringly normal on empty stores. If you have already started iron, say so when you book, and ask your doctor how long to hold it before the sample.
Iron deficiency without anaemia is real
Stores empty long before haemoglobin falls. In that window people report tiredness that sleep does not fix, hair fall, breathlessness on a flight of stairs, poor concentration and restless legs at night, all with a haemoglobin the report calls normal. A ferritin is the test that finds it. This is the single most common reason to check iron in a woman with heavy periods whose CBC looks acceptable.
When small red cells are not iron deficiency
Both iron deficiency and thalassaemia trait produce small, pale red cells, and on a CBC alone they can look similar. They are treated in opposite ways, so the distinction matters.
| Iron deficiency | Beta thalassaemia trait | |
|---|---|---|
| Ferritin | Low | Normal or high |
| RDW | Usually raised | Usually normal |
| Red cell count | Low or normal | Often high despite the low haemoglobin |
| MCV divided by red cell count | Above 13 | Below 13 |
| Confirmed by | Iron studies | Haemoglobin study by HPLC, with HbA2 above 3.5% |
That fourth row is the Mentzer index, and you can work it out from your own CBC. It is a pointer that tells the doctor which confirmatory test to order, and nothing more than that. The two conditions also coexist, and iron deficiency can suppress HbA2 enough to hide a trait, which is why the haemoglobin study is often repeated after iron has been replaced.
Why the trait matters here
Carrying one thalassaemia gene is usually silent. It gives mildly small red cells, sometimes a mildly low haemoglobin, and no symptoms worth treating. Studies screening populations across Gujarat have repeatedly found carriers at a few per cent, and higher in some communities, so it is not a rare finding in a Surat laboratory.
Two things follow. First, a carrier does not need iron unless they are separately iron deficient, and years of unnecessary iron is not a harmless thing to take. Second, when both partners carry the trait, each pregnancy carries a one in four chance of thalassaemia major, a condition requiring lifelong transfusion. Neither parent has any symptom that would warn them.
That is the whole argument for testing before marriage or early in pregnancy rather than after a child is diagnosed. Our Pre-Marital Screening panels and the ANC Profile both include the haemoglobin study for this reason.
Iron and B12 hide each other
Iron deficiency makes red cells small. B12 and folate deficiency make them large. Someone deficient in both can present with a perfectly normal MCV and a low haemoglobin nobody can explain, which is where a smear examination showing two distinct populations of cells earns its place. Our note on vitamin D and B12 covers the testing side of that in more detail.
Two situations that need a cause found, not a supplement
- Iron deficiency in a man, or in a woman past menopause. Without menstrual loss to explain it, the working assumption is slow blood loss from the digestive tract until a doctor has established otherwise. Correcting the haemoglobin without answering that question treats the number and leaves the reason in place.
- Anaemia that does not improve after four to six weeks of correct treatment. A reticulocyte count answers whether the marrow has responded at all, and a lack of response means the diagnosis needs revisiting rather than the dose increasing.
What to ask for
For a low haemoglobin with no obvious cause, the useful first set is a CBC with indices, ferritin with an inflammatory marker, and vitamin B12, with a haemoglobin study where the indices suggest a trait. That is close to what our Anemia Profile groups together, and the individual tests can be searched by name on the test list. Fasting is not required for any of them, and a sample can be collected at home if getting to a centre is difficult.
Anaemia is common, and most of the time the cause is straightforward and the treatment works. That is precisely why it is worth ten minutes and one extra test to be sure which cause you are treating.
- Anaemia
- Iron
- Thalassaemia
