What this test measures
Ferritin is the protein your body stores iron inside. Measuring it in blood gives a good estimate of how much iron you have banked — the reserve, not the amount in circulation.
This distinction is the whole point of the test, and it explains the result that confuses most people: a low ferritin with a completely normal haemoglobin.
Iron depletion happens in stages. Stores run down first, and ferritin falls. Then the supply to the bone marrow tightens, and transferrin saturation falls while haemoglobin holds. Only when the reserve is exhausted does haemoglobin start to drop and anaemia appear on the report. By the time a haemogram is abnormal, the process has been running for a long time.
So ferritin is an early warning, and haemoglobin is a late one. A normal blood count does not exclude iron deficiency; it only says you have not reached the last stage.
Ferritin has one significant weakness. It is also an acute-phase protein, which means it rises during infection, inflammation, liver disease and in obesity — regardless of how much iron is actually stored. That is why a CRP is often drawn alongside it, and why transferrin saturation earns its place: saturation is much less distorted by inflammation and can reveal a deficiency that a falsely reassuring ferritin has concealed.
In India this matters at scale. National survey data has repeatedly found anaemia in well over half of women of reproductive age, and iron deficiency is the dominant cause. Heavy menstrual bleeding, closely spaced pregnancies, predominantly plant-based diets in which iron is poorly absorbed, and tea or coffee taken with meals all contribute. The number of people with depleted stores and a normal haemoglobin is larger still, and largely uncounted.
What your result means
Start with the range printed on your own report — and then be aware that this is one of the tests where the printed lower limit is genuinely misleading. Many Indian laboratories print a lower limit of 10 to 13 ng/mL for women. A result of 14 ng/mL therefore arrives unflagged, while describing stores that are close to empty.
Ferritin below 15 ng/mL is diagnostic of iron deficiency in almost all circumstances.
Ferritin between 15 and 30 ng/mL is where most clinicians consider deficiency, particularly with symptoms. This is the band that a printed reference range most often misses.
Ferritin between 30 and 50 ng/mL with fatigue, hair shedding or restless legs is a grey zone. Transferrin saturation, the blood count indices and the clinical picture decide it, and reasonable doctors disagree here.
Ferritin below 100 ng/mL with a raised CRP may still represent deficiency, because inflammation has lifted the value.
Ferritin above the upper limit most often reflects inflammation, fatty liver, regular alcohol intake or a metabolic picture rather than iron overload. A high ferritin with a high transferrin saturation is the combination that raises the question of haemochromatosis and warrants proper assessment.
Two more cautions. Iron tablets and recent iron infusions raise ferritin for weeks, so a value drawn during treatment reflects the treatment. And a low ferritin is a finding, not a diagnosis — the more important question is why the iron went.
If the picture is low ferritin with a haemoglobin below the threshold, the clinical entity is covered in more depth on iron deficiency anaemia. If your haemoglobin is normal, this page is the right one — depleted stores without anaemia is a finding in its own right, not a lesser version of something else.
What each value means
Reference ranges differ between laboratories. Always read your result against the range printed on your own report.
Ferritin
Reference range
30 – 150 ng/mL
- What it means
- The protein that stores iron, and the best single measure of how much iron you have banked. Laboratories print wide ranges — often 13–150 ng/mL for women and 30–400 ng/mL for men — but a value below 30 ng/mL is where iron deficiency is generally considered, and below 15 ng/mL it is close to certain. Ferritin is reported in ng/mL and µg/L interchangeably; the numbers are identical.
- Why it matters
- A ferritin of 12 ng/mL with a normal haemoglobin means the iron stores are empty while the blood count still looks fine. This is iron deficiency without anaemia — the stage before haemoglobin falls — and it is very common in Indian women. Fatigue, hair shedding, breathlessness on stairs, poor concentration and restless legs can all be present here, and are often dismissed because the haemogram reads normal.
- Next step
- Have it read alongside a full blood count, transferrin saturation and CRP, and — this is the part that matters — have the reason for the loss looked for rather than only the number corrected. Do not start iron on your own; the dose, the form and the duration depend on the cause.
Interpret in context. One result doesn't tell the whole story.
Haemoglobin
12 – 16 g/dL
The oxygen-carrying protein in red cells. The World Health Organization defines anaemia as below 12.0 g/dL in non-pregnant women, below 11.0 g/dL in pregnancy and below 13.0 g/dL in men. Haemoglobin is the last thing to fall in iron deficiency, which is why a normal value does not rule it out.
Transferrin saturation
20 – 45 %
The proportion of your iron-transport capacity currently carrying iron. Below 20 percent supports iron deficiency and is particularly useful when ferritin is ambiguous, because it is far less affected by inflammation. Persistently above 45 percent raises the question of iron overload.
Serum iron
60 – 170 µg/dL
Iron in transit in the blood at the moment of the draw. It swings widely through the day and rises for hours after an iron tablet or an iron-rich meal, so on its own it is close to uninterpretable. It exists mainly to be divided by TIBC to give the saturation.
Total iron binding capacity (TIBC)
250 – 450 µg/dL
How much iron your blood could carry if it were full. It rises in iron deficiency — the body increases transport capacity when stores run down — which makes a high TIBC with a low ferritin a coherent picture rather than a contradictory one.
CRP
0 – 5 mg/L
A marker of inflammation, included because ferritin rises during any inflammatory state regardless of iron stores. A normal CRP means a low ferritin can be taken at face value. A raised CRP means a normal-looking ferritin may still be masking deficiency, and ferritin thresholds as high as 70–100 ng/mL are used in that setting.
This is general education and cannot account for your history, your examination or your reports. If you need advice specific to your health, we’re always happy to see you in consultation.
What to do next
Look for the cause, not just the number. This is the part most often skipped, and it is the part that matters. In women of reproductive age, heavy menstrual bleeding is the commonest reason and is frequently under-reported because it has felt normal for as long as they can remember. In men and in women past menopause, a low ferritin is taken more seriously still, because blood loss from the gut is a leading explanation and is often silent. Coeliac disease, H. pylori infection, long-term acid-suppressing medication and a diet low in absorbable iron are the other regular contributors in India.
Have it read as a set. A full blood count with red cell indices, transferrin saturation, TIBC and CRP together give a far clearer picture than ferritin alone. Adding vitamin B12 is common practice here, because combined deficiency is frequent and each can mask the other's effect on cell size.
Wait long enough before rechecking. Ferritin rebuilds slowly. Stores take three to six months to refill after haemoglobin has recovered, which is why treatment courses are longer than people expect and why rechecking at four weeks tells you little.
Do not begin iron on your own. The dose, the form, the frequency and the length of the course all depend on the cause and on how well you absorb it — and taking iron before the reason has been looked for can delay finding something that needed finding. That conversation belongs with your doctor.
This information is educational and not a diagnosis.
Alitheau Learning Sessions
Understanding Blood Reports
- Why reference ranges differ between laboratories, and what that means for you
- How to read a liver function test, and why the pattern beats the worst number
- What HbA1c actually measures, and the common things that distort it
One result rarely tells the whole story
Have this read alongside everything else.
Conditions this result comes up in
Questions people ask
Yes. Ferritin measures stores; haemoglobin measures what is currently in circulation. Stores empty first, and the body protects haemoglobin until they are gone. Iron deficiency without anaemia is a recognised finding, is far more common than iron deficiency anaemia, and is associated with fatigue, reduced exercise capacity, hair shedding and restless legs. A normal haemogram does not exclude it.
Below 30 ng/mL is the threshold most commonly used clinically, because it identifies absent bone-marrow iron with good accuracy. Below 15 ng/mL is close to diagnostic. Many Indian laboratories print a lower limit of 10 to 13 ng/mL for women, which is why a genuinely depleted result can arrive without a flag next to it.
It can. Ferritin rises with infection, inflammation, liver disease, obesity and after surgery, and that rise is independent of iron stores. When CRP is raised, ferritin is interpreted against a higher threshold and transferrin saturation becomes the more reliable number.
Most raised ferritin in practice reflects inflammation, fatty liver, regular alcohol or a metabolic picture rather than iron overload. Genuine iron overload, including haemochromatosis, is usually accompanied by a high transferrin saturation, which is why the two are read together.
Ferritin itself does not require fasting. Serum iron and transferrin saturation vary through the day and are usually drawn in the morning, and iron supplements are typically paused for a day or two beforehand — check what your laboratory and your doctor advise.