Ferritin and iron studies explained: normal ranges, low iron and what to do next.

Iron studies are a set of blood tests that show how much iron your body has stored, how much is circulating, and how well it is being carried. Ferritin is the store, and it is the most useful single number. A full blood count alongside it shows whether low iron has gone on long enough to become anaemia. Here is how to read them.

What iron studies include, and why the full blood count matters

A standard set of iron studies in Australia reports four things, and most doctors add a full blood count so the two can be read together.

• Ferritin: a protein that stores iron inside your cells. The blood level mirrors your total iron reserve, so it is the marker that shows deficiency earliest.
• Serum iron: the iron travelling in your blood at the moment of the draw. It moves with meals, time of day and recent supplements, so on its own it is the least reliable of the four.
• Transferrin: the protein that carries iron around your body. When stores are low your liver makes more of it, so transferrin tends to rise as iron falls.
• Transferrin saturation: the percentage of transferrin that is actually carrying iron. Low saturation means the carriers are running empty; high saturation is a flag for iron overload.
• Full blood count (FBC): counts your red cells and measures haemoglobin, the protein inside them that carries oxygen. It also reports red cell size, which tends to shrink when iron has been low for a long time.

Think of it as a supply chain. Ferritin is the warehouse, transferrin the delivery truck, saturation how full the truck is, and haemoglobin the product on the shelf. The warehouse empties first; the shelf runs bare last.

Reference ranges, and why "normal" ferritin can still be low for your symptoms

Every laboratory prints its own reference interval next to each result, and intervals differ a little between labs. The table gives typical adult figures for Australian women so you can orient yourself.

Ranges vary by laboratory; your report shows the range your lab uses. Typical ranges on this page are drawn from Pathology Tests Explained (RCPA) and the sources listed below.

Here is the part that catches women out. A ferritin of 18 ug/L can be printed in black, inside the reference interval, on a report from a lab whose lower limit is 15. Technically normal. But many Australian clinicians consider a ferritin under about 30 ug/L to represent depleted stores in a woman with symptoms. Reference intervals describe what is common in a population, not what is optimal for you, and where low iron is widespread among women, "common" and "healthy" are not the same thing.

Low ferritin with normal haemoglobin: the stage that gets missed

Iron deficiency is a process, not a switch. First your stores fall and ferritin drops. Haemoglobin stays normal because your body protects red cell production for as long as it can. Only when the warehouse is nearly empty does haemoglobin start to slide and anaemia appear on the full blood count.

That first stage is called iron deficiency without anaemia, and it is where a lot of women live for years. Because a routine full blood count looks fine, nobody orders ferritin, and the tiredness gets put down to work, parenting, stress or "just hormones". Yet the symptoms of the early stage are real: fatigue, poor concentration, low mood, restless legs, hair shedding, feeling the cold and reduced exercise tolerance are all reported by women whose haemoglobin is entirely normal.

This is why iron studies, not a blood count alone, are the right test when you feel run down. A full blood count answers "am I anaemic?". Ferritin answers "am I running out of iron?", usually the more useful question.

High ferritin: inflammation, and when a doctor looks further

Ferritin has a second job that complicates things. It rises in response to inflammation, infection, liver stress and, to a lesser degree, regular alcohol intake. Doctors call it an acute-phase reactant. So a raised ferritin, especially a mildly raised one, is far more often a sign that something inflammatory is going on than a sign of too much iron. The reverse matters too: where inflammation is present, doctors treat a ferritin under about 70 ug/L as still compatible with low iron stores, which is why CRP is read beside it.

The way to tell the difference is transferrin saturation. In inflammation, ferritin is up but saturation is normal or low, because iron is being locked away rather than overloaded. In genuine iron overload, both ferritin and saturation are high. A doctor who sees that second pattern will usually repeat the test fasting and, if it persists, consider a genetic test for hereditary haemochromatosis, an inherited iron-loading condition that is relatively common in people of northern European background.

Ferritin is not, in everyday practice, a "tumour marker". It rises in many ordinary conditions and is never read in isolation: your doctor looks at saturation, liver tests, CRP and your history before deciding whether anything needs following up.

Iron and periods, pregnancy, postpartum and perimenopause

Women lose iron every month in a way men do not, and each life stage adds its own pressure on stores.

• Heavy periods: the leading cause of low iron in women of reproductive age. If you soak through protection every one to two hours, pass large clots or bleed for more than seven days, your monthly loss may exceed what food can replace. Read more in low iron and heavy periods.
• Pregnancy: blood volume expands and the baby draws on your iron. Ferritin is checked early in pregnancy and again later; it commonly falls through the second and third trimesters even when the diet is good.
• Postpartum: blood loss at birth and the demands of feeding leave many women depleted in the months after a baby, at exactly the time exhaustion is dismissed as normal new-parent tiredness. Iron studies are a core part of a postpartum blood check.
• Perimenopause: cycles in the transition years are often heavier and closer together before they stop, so iron can drop sharply in the forties. Low iron also mimics perimenopause almost perfectly, which is why it sits in the perimenopause panel.

Preparing for the test

Iron studies can be collected at any time of day and fasting is not required, although a morning collection gives the most consistent serum iron and saturation. If you take iron, mention it: a dose in the hours before the draw pushes serum iron and saturation up and can flatter the result. Do not test while you have a cold, flu or any acute illness, or for a couple of weeks after an infection, because inflammation can push ferritin into the normal range and hide a deficiency. A recent transfusion or iron infusion also changes the picture for at least four weeks, so retesting is usually deferred for one to two months; tell your doctor either way.

Reading your KnowLuna iron result

Your KnowLuna report shows each marker against the laboratory range with a plain-English note beside it, and it reads the set together rather than line by line. A low ferritin with normal haemoglobin is called out as depleted stores, not filed as "normal". A high ferritin is read against saturation so you know whether it looks inflammatory or iron-related. Anything needing prompt attention is followed up by a doctor.

If you add the doctor consult, the doctor talks through why your iron might be low, whether your periods are part of the picture, and the sensible next steps. Your GP can use the same report.

Common questions

Sources and further reading

• Pathology Tests Explained (RCPA): ferritin
• Pathology Tests Explained (RCPA): iron studies
• World Health Organization: guideline on use of ferritin concentrations to assess iron status in individuals and populations (2020)
• Healthdirect: iron deficiency
• Healthdirect: iron studies blood test
• Better Health Channel: iron deficiency in adults
• NHMRC Nutrient Reference Values: iron

General information only, not medical advice. If your symptoms are severe or sudden, see a doctor promptly. This page does not replace a consultation with a doctor who knows your history; read our medical disclaimer.