Ferritin and Iron Blood Tests: What Low or High Results Mean

Low ferritin is one of the most common reasons people feel tired. But ferritin can also be falsely reassuring, because it rises during inflammation.

Imagine feeling drained, breathless on the stairs and losing more hair than usual. Your haemoglobin is normal, but your ferritin is 9. You may be iron deficient without anaemia.

What the tests measure

• Ferritin: the body’s iron stores
• Serum iron: iron in the blood, which varies through the day
• Transferrin saturation: how much of the iron-carrying protein is loaded with iron
• TIBC: total iron-binding capacity, which rises when iron is low

Low ferritin

• Strongly suggests iron deficiency
• Many clinicians consider ferritin below about 30 µg/L to suggest low iron stores in adults
• Causes include heavy periods, pregnancy, low dietary iron and bleeding from the gut
• Unexplained iron deficiency in men or post-menopausal women needs investigation

High ferritin

• Inflammation or infection
• Liver disease and alcohol
• Obesity and metabolic syndrome
• Iron overload, such as haemochromatosis, often with high transferrin saturation

Treatment of iron deficiency

Treatment usually involves oral iron, sometimes on alternate days to improve absorption and reduce side effects, or intravenous iron when needed. The cause should always be looked for.

Lab ranges vary

Reference ranges differ between laboratories and countries, and some use different units. Always compare your result with the range printed on your report and discuss it with your healthcare provider.

Iron deficiency is the most common nutritional problem in the world

The World Health Organization estimates that anaemia affects hundreds of millions of people worldwide, and iron deficiency is a leading cause. Women of reproductive age, pregnant women, young children and people with heavy periods are most affected.

Iron deficiency can cause symptoms before it causes anaemia. These include tiredness, poor concentration, headaches, breathlessness on exertion, restless legs, brittle nails, hair loss and cravings for ice or non-food items (pica).

How ferritin fits with the full blood count

A full blood count shows haemoglobin and the size of red blood cells. In iron deficiency, red cells often become smaller and paler (low MCV and MCH) before haemoglobin falls. Ferritin then confirms whether low iron stores are the cause.

Because ferritin also rises with inflammation, a “normal” ferritin in someone with an infection, arthritis, kidney disease or obesity may hide iron deficiency. In these situations, transferrin saturation below about 20% can be a helpful clue.

Finding the cause of iron deficiency

Iron deficiency is a sign, not a diagnosis. Common causes include heavy periods, pregnancy, blood donation, poor dietary intake, coeliac disease, and blood loss from the stomach or bowel.

In men and in women after the menopause, unexplained iron deficiency anaemia needs investigation of the gut, often with a camera test, because it can be the first sign of bowel or stomach cancer. In some countries, hookworm infection is also an important cause.

Getting the most from iron tablets

• Take iron with water or orange juice, as vitamin C helps absorption
• Avoid taking it with tea, coffee, milk or antacids
• Taking it once a day or on alternate days may work as well as more frequent doses and cause fewer side effects
• Expect dark stools; this is normal
• Constipation or stomach upset are common; ask about other preparations if they are a problem
• Keep iron tablets out of reach of children, as overdose can be fatal

How long treatment takes

Haemoglobin usually starts rising within two to four weeks of starting iron. Many people need to continue for about three months after haemoglobin returns to normal to rebuild iron stores. Your healthcare provider will usually repeat blood tests to check progress.

Iron-rich foods

• Red meat, liver (avoid liver in pregnancy) and poultry
• Fish
• Beans, lentils and chickpeas
• Dark green leafy vegetables
• Fortified breakfast cereals
• Dried fruit, nuts and seeds
• Iron from plant foods is absorbed less well, so pair them with vitamin C-rich foods

When high ferritin is a concern

Haemochromatosis is an inherited condition, particularly common in people of northern European descent, in which the body absorbs too much iron. Over time, iron builds up in the liver, heart, pancreas and joints. It is suspected when both ferritin and transferrin saturation are high, and can be confirmed with a genetic test. Treatment, usually regular removal of blood, is simple and effective.

Iron in pregnancy

The body needs much more iron in pregnancy to support the growing baby, placenta and increased blood volume. Iron deficiency in pregnancy is linked with tiredness, a higher chance of needing a blood transfusion after birth, and possible effects on the baby, such as low birth weight.

Many antenatal services check haemoglobin early in pregnancy and again around 28 weeks, and some check ferritin. If iron is low, iron tablets are usually recommended, and intravenous iron may be offered later in pregnancy if tablets are not working.

Iron and heavy periods

Heavy menstrual bleeding is one of the most common causes of iron deficiency, yet many people do not realise their periods are heavier than normal. Signs include needing to change pads or tampons every one to two hours, passing large clots, bleeding through clothes or bedding, or periods lasting more than seven days. Treating the cause of heavy periods is just as important as replacing iron, so talk to your healthcare provider about options.

Questions to ask about your iron results

• What is my ferritin and transferrin saturation?
• Could inflammation be affecting my ferritin?
• What is causing my low iron, and do I need further tests?
• How long should I take iron, and when will you recheck my blood?

Frequently asked questions

Can I have low ferritin with normal haemoglobin?

Yes. This is iron deficiency without anaemia, and it can still cause symptoms.

Should I take iron supplements without a test?

It is better to test first. Too much iron can be harmful.

Can I donate blood if my ferritin is low?

Blood services check haemoglobin before donation, and some also check ferritin. Frequent donors can develop low iron stores.

Is IV iron better than tablets?

IV iron works faster and is useful when tablets fail, are not tolerated or iron is needed quickly, for example before surgery or late in pregnancy.

Can I have iron deficiency without symptoms?

Yes. Mild deficiency may cause no obvious symptoms.

But my ferritin is normal and I’m still tired

Ferritin can look normal during inflammation. Ask whether transferrin saturation or other tests are needed.

Related: Anaemia: symptoms and iron-rich foods · Full blood count explained

Sources: World Health Organization guideline on ferritin (2020), British Society of Gastroenterology iron deficiency anaemia guidelines, NHS, Lab Tests Online UK.