You can have a perfectly normal haemoglobin and still feel exhausted, foggy, and short of breath. This is one of the most common and most overlooked patterns in UK blood test results, and ferritin is usually the explanation.
Ferritin is the main storage protein for iron in the body. When it is low, your iron reserves are depleted. Your body can still be making enough haemoglobin for now, drawing on whatever iron remains in circulation, but the reserves are gone. The symptoms arrive well before the full picture shows up as anaemia.
- What ferritin actually is and why it matters
- What is a normal ferritin level in the UK
- Symptoms of low ferritin
- Why your haemoglobin can be normal and you still feel terrible
- What causes low ferritin
- The rest of the iron panel explained
- Why high ferritin does not rule out iron deficiency
- What to do if your ferritin is low
- Check your iron results
What ferritin actually is and why it matters
Iron in the body exists in two main forms: the iron currently in circulation, carried by a protein called transferrin, and the iron in storage, held inside a protein called ferritin. Ferritin is found mainly in the liver, bone marrow, spleen, and muscle tissue. A small amount is released into the blood, and it is this serum ferritin level that appears on your blood test.
Ferritin is the body's iron reserve. When dietary iron intake drops, or iron losses increase, the body draws on ferritin stores to keep circulating iron and haemoglobin levels stable. Ferritin falls first. Haemoglobin falls later, if at all.
This sequence is why ferritin is the most sensitive early marker of iron deficiency. By the time haemoglobin drops enough to diagnose anaemia, ferritin has often been depleted for months.
What is a normal ferritin level in the UK
Reference ranges vary slightly between UK laboratories, but the broadly accepted thresholds are:
| Ferritin level | Interpretation |
|---|---|
| Below 15 µg/L | Iron deficiency confirmed |
| 15 to 30 µg/L | Depleted stores, likely iron deficiency |
| 30 to 200 µg/L | Normal range for most adults |
| Above 200 µg/L | Elevated, warrants investigation |
Some clinicians use 30 µg/L as their functional threshold rather than 15. A ferritin between 15 and 30 may fall within the laboratory's printed normal range, but symptoms of iron deficiency can be present at these levels. This is a frequent source of frustration: a GP reports the result as normal, but the patient is symptomatic.
The normal range also differs by sex. Many laboratories quote a broader range for males, typically up to 300 µg/L, and a narrower range for females, typically up to 150 µg/L. The lower end of the range is similar between sexes.
Symptoms of low ferritin
The symptoms of depleted iron stores often begin before any anaemia is detectable. The most commonly reported are:
- Persistent fatigue and low energy, even after adequate sleep
- Brain fog, difficulty concentrating, and poor short-term memory
- Restless legs syndrome, particularly at night
- Shortness of breath on mild exertion
- Heart palpitations
- Brittle or spoon-shaped nails
- Hair thinning or increased hair shedding
- Pale skin, pale inner eyelids, or pale nail beds
- Reduced exercise tolerance
- Feeling cold when others are comfortable
Fatigue and brain fog are the two symptoms that most consistently improve with iron supplementation in people with low ferritin, even when haemoglobin is normal. Restless legs syndrome has a particularly strong association with iron deficiency, and ferritin testing is recommended in anyone presenting with it.
Why your haemoglobin can be normal and you still feel terrible
The body protects haemoglobin levels at the expense of ferritin stores. When iron availability drops, the priority is to keep red blood cells carrying oxygen around the body. The body will deplete ferritin completely before it allows haemoglobin to fall.
This means you can have a ferritin of 8 µg/L, deeply depleted, while your haemoglobin sits at 128 g/L, within normal range. A full blood count will look unremarkable. Only a ferritin measurement will reveal what is happening.
This stage is called iron deficiency without anaemia, and it is considerably more common than iron deficiency anaemia. Many people with this pattern are told their blood test is normal, because the ferritin was not checked or the result was not flagged. Their symptoms are real, and the explanation is in the iron panel.
What causes low ferritin
Inadequate dietary intake
Iron is found in two forms in food. Haem iron, found in red meat, poultry, and fish, is absorbed efficiently. Non-haem iron, found in plant foods such as lentils, beans, tofu, spinach, and fortified cereals, is less well absorbed. People following vegan or vegetarian diets have a higher risk of iron deficiency because of this difference in bioavailability.
Vitamin C consumed alongside non-haem iron significantly improves absorption. Tannins in tea and coffee, and calcium in dairy, reduce it. Timing food and drink around iron intake makes a meaningful difference.
Blood loss
Menstrual blood loss is the most common cause of iron deficiency in women of reproductive age. Heavier periods, particularly those associated with fibroids or other gynaecological conditions, can deplete ferritin faster than diet can replenish it. This is why iron deficiency is substantially more prevalent in women aged 18 to 45 than in any other group.
Gastrointestinal blood loss, from conditions such as peptic ulcer disease, inflammatory bowel disease, coeliac disease, or colorectal cancer, is the most important cause in men and in post-menopausal women. Any unexplained iron deficiency in this group warrants investigation for a source of bleeding.
Regular blood donation reduces ferritin over time, particularly in people who donate frequently.
Malabsorption
The small intestine, specifically the duodenum and upper jejunum, is where iron is absorbed. Conditions that damage or inflame this region reduce absorption. Coeliac disease is a particularly common and frequently undiagnosed cause. Approximately 1 in 100 people in the UK have coeliac disease, and iron deficiency anaemia is one of its most common presentations.
Helicobacter pylori infection, inflammatory bowel disease, and previous gastric surgery also impair iron absorption.
Increased demand
Pregnancy significantly increases iron requirements. The developing foetus draws on maternal iron stores, and the increase in blood volume during pregnancy raises demand further. Iron supplementation is recommended during pregnancy in the UK, and ferritin is routinely monitored.
Athletes, particularly endurance athletes, have higher iron requirements due to increased losses through sweat, gastrointestinal microbleeding, and foot-strike haemolysis in runners.
The rest of the iron panel explained
Ferritin is the most important marker, but a full iron panel includes three other values that help clarify what is happening.
Serum iron
Serum iron measures the iron currently circulating in the blood, bound to transferrin. It is a less reliable marker than ferritin because it fluctuates significantly across the day and in response to recent meals. A low serum iron supports iron deficiency but is not diagnostic on its own.
TIBC (total iron-binding capacity)
TIBC measures the maximum amount of iron that transferrin in the blood could carry. When iron is low, the liver produces more transferrin, increasing TIBC. A high TIBC alongside low serum iron is the classic pattern of iron deficiency. A low TIBC can indicate iron overload or chronic disease.
Transferrin saturation
This is the percentage of transferrin that is currently carrying iron. The formula is serum iron divided by TIBC, expressed as a percentage. A normal range is roughly 20 to 50%. Below 16% indicates iron deficiency. Above 45% may indicate iron overload.
The combination of low ferritin, low serum iron, high TIBC, and low transferrin saturation confirms iron deficiency. When ferritin is elevated but transferrin saturation is also high, iron overload, including hereditary haemochromatosis, should be considered.
Why high ferritin does not rule out iron deficiency
Ferritin is an acute phase protein. This means it rises in response to inflammation, infection, liver disease, and some cancers, independently of iron stores. A patient with severe iron deficiency and an active inflammatory condition can have a normal or elevated ferritin, masking the deficiency.
This pattern is called functional iron deficiency, and it is common in conditions such as rheumatoid arthritis, inflammatory bowel disease, and chronic kidney disease. In these cases, transferrin saturation is more informative than ferritin alone. A transferrin saturation below 20% in the context of raised ferritin and an inflammatory condition strongly suggests functional iron deficiency.
What to do if your ferritin is low
If your ferritin is below 30 µg/L and you have symptoms, the following steps are worth taking.
Review your diet, particularly iron sources and the factors that help or hinder absorption. Increasing haem iron intake, combining plant-based iron with vitamin C, and separating iron-rich meals from tea, coffee, and dairy can all make a meaningful difference over weeks to months.
Speak to your GP or pharmacist about iron supplementation. Ferrous sulfate 200mg three times daily is the standard NHS recommendation for iron deficiency. It is inexpensive and effective, though it can cause gastrointestinal side effects. Ferrous gluconate and ferrous fumarate are alternatives with slightly better tolerability. Iron bisglycinate, available over the counter, tends to cause fewer side effects and may be worth trying if standard iron supplements are not well tolerated.
Investigate the cause. Particularly in men, post-menopausal women, or anyone with unexplained iron deficiency, further investigation for a source of bleeding is important. Coeliac screen is worth considering in anyone with persistent iron deficiency despite adequate intake and supplementation.
Recheck ferritin after three months of supplementation. Ferritin rises more slowly than haemoglobin. A full repletion of stores can take six months or longer.
Check your iron results
If you have your iron panel results and want to understand what each number means, the free blood test explainer covers the full iron studies panel. Enter your ferritin, serum iron, TIBC, and transferrin saturation to see where each value sits against the reference range, with plain-English explanations of what the pattern means.
The iron panel is one of eight panels covered in the tool, alongside FBC, liver function, thyroid, kidney, HbA1c, lipid profile, and bone profile.
Explore the free blood test explainer
This article is for general information only. It is not a substitute for clinical assessment. If you are concerned about your iron levels or have symptoms that may indicate iron deficiency, speak to your GP or pharmacist.
