Iron deficiency without anaemia: what ferritin and transferrin saturation tell you

Many people think of iron deficiency and anaemia as the same thing. They are not. Anaemia is the late stage, when there is so little iron that the body can no longer make enough haemoglobin. Before that, there is often a long stretch where iron stores are running down and haemoglobin still looks normal.

This earlier stage is called iron deficiency without anaemia. It is common, particularly in women who menstruate, and it can still cause symptoms. A full blood count alone will miss it. Iron studies will not.

How the body handles iron

Iron is absorbed from food in the gut, carried in the blood by a protein called transferrin, and stored mainly in the liver as ferritin. Most of the body's iron is used to make haemoglobin in new red cells. When losses outpace intake, the body first draws on its stores. Only when the stores are nearly empty does haemoglobin start to fall.

Ferritin: your iron savings account

A small amount of ferritin leaks into the blood in proportion to what is stored, so the blood level is a good guide to your reserves. A low ferritin is the most reliable single sign of iron deficiency. LifePrint uses the WHO 2020 guideline: in adults, a ferritin below 15 ug/L means iron deficiency.

Between 15 and 30 ug/L, LifePrint reports a grey zone of low iron stores. This is above the WHO deficiency cut-off, but many people with symptoms in this range turn out to be iron deficient, so your report explains the result in the context of your other markers rather than calling it normal.

Transferrin saturation: iron in transit

Transferrin saturation tells you what share of the iron-carrying protein in your blood is actually loaded with iron. It reflects the iron available to your tissues right now. A saturation below 20% supports iron deficiency, especially alongside a low or borderline ferritin. It is useful when ferritin is hard to read because of inflammation.

Two related markers complete the picture. TIBC, or total iron binding capacity, tends to rise when iron is short, as the body makes more transferrin to catch whatever iron it can. Serum iron itself swings a lot with meals and the time of day, so on its own it is the least reliable of the four.

Symptoms of low iron stores

• Tiredness and low stamina, especially during exercise.
• Difficulty concentrating.
• Hair shedding.
• Restless legs, particularly in the evening.
• Brittle nails or cravings for ice.

None of these is specific to iron, which is why testing is better than guessing.

Who is most at risk

• Women with heavy or long periods.
• Pregnant women and those who have recently given birth.
• Regular blood donors.
• People on vegetarian or vegan diets, since iron from plants is less easily absorbed.
• Endurance athletes, particularly runners.
• People with coeliac disease or other conditions that affect absorption in the gut.

Low iron in men and after menopause

Men and women after menopause do not lose iron through periods, so a low ferritin in these groups needs a reason. The most important one to rule out is slow bleeding from the stomach or bowel, which can be caused by ulcers, polyps or, less often, cancer. If your ferritin is low and you are in one of these groups, see a doctor, who may suggest further tests of the gut. Please do not simply take iron and move on.

When iron is high

Iron studies also pick up the opposite problem. A transferrin saturation above 45%, or a ferritin above 500 ug/L, warrants a check for iron overload. Inherited haemochromatosis is one cause. Much more often a high ferritin reflects inflammation, alcohol or a fatty liver. This is one reason not to take iron without a test: extra iron is not harmless if you already have enough.

Getting a reliable result

Test when you are well, not during or just after a cold or flu, because illness raises ferritin and lowers serum iron. If you take an iron supplement, tell us, as it changes the results. Your LifePrint report reads the four iron markers together, flags anything that needs a doctor and shows how urgently.

If your results suggest iron deficiency, speak to a registered healthcare practitioner. They can confirm it, look for the cause and advise on the right treatment and how to recheck it.