Iron Blood Test: Normal Ranges, Causes & What Your Results Mean

What Is Iron?

Iron is an essential mineral that plays a fundamental role in human health. It is a key component of haemoglobin, the protein in red blood cells that carries oxygen from your lungs to every tissue and organ in your body. Iron is also present in myoglobin (which stores oxygen in muscles), is critical for energy production within cells, and plays roles in DNA synthesis, immune function, and cognitive development.

The body contains approximately 3-5 grams of iron in total. About 65-70% is found in haemoglobin, with the remainder stored as ferritin and haemosiderin (primarily in the liver, spleen, and bone marrow) or incorporated into enzymes and other proteins throughout the body.

Iron homeostasis is tightly regulated because both deficiency and excess are harmful. The body has no active mechanism for excreting iron — losses occur primarily through shed skin cells, gastrointestinal tract cells, and in women, menstrual blood. Iron absorption from the diet is therefore the main regulatory mechanism, controlled by hepcidin, a hormone produced by the liver.

When your GP orders an "iron" blood test, the panel typically includes several related markers:

• Serum iron: The amount of iron circulating in your blood, bound to the transport protein transferrin
• Ferritin: Reflects your iron stores; the most sensitive early marker of iron deficiency
• Transferrin / Total iron-binding capacity (TIBC): Measures the capacity of transferrin to bind iron; rises when iron stores are low
• Transferrin saturation: The percentage of transferrin that is carrying iron; a key marker for iron overload

Iron deficiency is the most common nutritional deficiency worldwide, affecting approximately 1 in 4 people globally. In the UK, it is particularly prevalent among women of reproductive age, pregnant women, young children, and people following restrictive diets.

Why Is Iron Tested?

Iron testing is one of the most commonly ordered blood investigations for good reason:

• Anaemia investigation: Iron deficiency is the most common cause of anaemia worldwide. If a full blood count reveals low haemoglobin or microcytic (small) red blood cells, iron studies are the logical next step to confirm the diagnosis.
• Fatigue and tiredness: Persistent fatigue is one of the leading reasons people seek medical attention. Iron deficiency — even without anaemia — can cause significant tiredness, reduced exercise capacity, and difficulty concentrating.
• Heavy menstrual periods: Women with heavy periods (menorrhagia) are at high risk of iron depletion. Regular iron monitoring helps prevent anaemia and guides supplementation.
• Pregnancy: Iron requirements increase substantially during pregnancy. NICE recommends testing ferritin at the booking appointment and monitoring haemoglobin throughout pregnancy.
• Gastrointestinal investigation: Iron deficiency in men and post-menopausal women is a red flag that warrants investigation for gastrointestinal blood loss (coeliac disease, peptic ulcers, colorectal cancer, inflammatory bowel disease). NICE guidelines recommend urgent referral for colonoscopy and gastroscopy in this population.
• Restless legs syndrome: Iron deficiency is a treatable cause of restless legs syndrome. Guidelines recommend checking ferritin, with supplementation advised if levels are below 75 µg/L.
• Iron overload screening: Hereditary haemochromatosis is the most common genetic disorder in people of Northern European descent, affecting approximately 1 in 200 people. Iron studies (particularly transferrin saturation) are the initial screening test.
• Dietary assessment: Vegetarians, vegans, and people with restrictive diets are at increased risk of iron deficiency. Regular monitoring ensures adequate intake.

Normal Ranges

Iron status is best assessed by looking at multiple markers together. The following table shows typical UK adult reference ranges:

Marker	Normal Range (Male)	Normal Range (Female)	Units
Serum iron	10.6 – 28.3	6.6 – 26.0	µmol/L
Ferritin	30 – 400	13 – 150	µg/L
Transferrin	2.0 – 3.6	2.0 – 3.6	g/L
TIBC	45 – 72	45 – 72	µmol/L
Transferrin saturation	20 – 50%	15 – 50%	%

Important notes on interpretation:

• Ferritin is the single most useful marker for iron deficiency. A ferritin below 30 µg/L is widely accepted as indicating depleted iron stores, even if haemoglobin is still normal. Some experts recommend a threshold of 50 µg/L for symptomatic patients.
• Ferritin is an acute-phase reactant — it rises during inflammation, infection, and liver disease, potentially masking iron deficiency. If CRP is elevated alongside a "normal" ferritin, the true iron status may be worse than the ferritin suggests.
• Transferrin saturation above 45% (or above 50% in some guidelines) raises suspicion for iron overload and should prompt investigation for haemochromatosis, including HFE gene testing.
• Serum iron fluctuates significantly throughout the day and with meals, making it less reliable as a standalone marker.

What Do High Iron Levels Mean?

Elevated iron markers — particularly high ferritin and high transferrin saturation — can indicate:

• Hereditary haemochromatosis: The most common genetic cause of iron overload in the UK. Mutations in the HFE gene (most commonly C282Y) cause excessive iron absorption from the diet. Untreated, iron accumulates in the liver, heart, pancreas, and joints, leading to cirrhosis, cardiomyopathy, diabetes, arthritis, and skin bronzing. Early diagnosis and regular venesection (blood removal) prevents complications.
• Secondary iron overload: Repeated blood transfusions (in conditions such as thalassaemia, sickle cell disease, or myelodysplastic syndrome) can lead to iron accumulation requiring chelation therapy.
• Inflammation or infection: Ferritin rises as an acute-phase response. Very high ferritin (above 1,000 µg/L) in the context of acute illness may reflect systemic inflammation rather than true iron overload. Adult-onset Still's disease and haemophagocytic lymphohistiocytosis (HLH) can cause extremely high ferritin levels.
• Liver disease: Chronic liver conditions (alcoholic liver disease, non-alcoholic fatty liver disease, viral hepatitis) can elevate ferritin through inflammation and hepatocyte damage.
• Excessive supplementation: Taking high-dose iron supplements when not deficient can raise iron levels. Acute iron poisoning (particularly in children) is a medical emergency.
• Metabolic syndrome: Elevated ferritin is common in metabolic syndrome and type 2 diabetes, reflecting both inflammation and mild iron excess.

What Do Low Iron Levels Mean?

Low iron is extremely common and has many potential causes:

• Iron deficiency anaemia: The most advanced stage of iron depletion, where haemoglobin has fallen below normal. Symptoms include fatigue, pallor, breathlessness, dizziness, cold hands and feet, brittle nails, and pica (craving non-food items).
• Heavy menstrual periods: The most common cause of iron deficiency in premenopausal women. Monthly blood loss depletes iron stores faster than dietary intake can replace them.
• Inadequate dietary intake: Vegetarian and vegan diets, restrictive eating, and poor-quality diets low in iron-rich foods can lead to deficiency. Non-haem iron (from plant sources) is less readily absorbed than haem iron (from meat).
• Gastrointestinal blood loss: Peptic ulcers, colorectal polyps, colorectal cancer, gastritis, oesophagitis, and use of NSAIDs or aspirin can cause chronic blood loss. NICE recommends that iron deficiency in men and postmenopausal women should prompt urgent gastrointestinal investigation.
• Malabsorption: Coeliac disease, inflammatory bowel disease (Crohn's disease), bariatric surgery, atrophic gastritis, and H. pylori infection can all impair iron absorption.
• Pregnancy: Iron requirements roughly double during pregnancy to support the growing foetus, placenta, and expanded maternal blood volume.
• Chronic kidney disease: Reduced erythropoietin production and chronic inflammation in CKD contribute to iron-restricted erythropoiesis.
• Intense exercise: Endurance athletes, particularly runners, can develop iron deficiency through a combination of gastrointestinal blood loss, haemolysis (footstrike haemolysis), sweat losses, and hepcidin elevation after exercise.

How to Improve Your Iron Levels

Dietary Strategies

• Eat iron-rich foods: Haem iron (from animal sources) is the most readily absorbed form. Excellent sources include red meat, liver, dark poultry meat, mussels, and oysters. Non-haem iron sources include dark green leafy vegetables (spinach, kale), legumes (lentils, chickpeas, beans), fortified cereals, tofu, and dried fruits.
• Enhance absorption with vitamin C: Consuming vitamin C alongside iron-rich foods significantly increases non-haem iron absorption. Pair meals with citrus fruits, peppers, tomatoes, or a glass of orange juice.
• Avoid absorption inhibitors at mealtimes: Tea, coffee, and calcium-rich foods (milk, cheese) contain compounds that reduce iron absorption when consumed at the same time as iron-rich foods. Consider having these between meals rather than with them.
• Cook with cast iron: Cooking acidic foods (such as tomato-based sauces) in cast iron cookware can increase the iron content of the meal.

Supplementation

• Oral iron supplements: Ferrous sulphate, ferrous fumarate, or ferrous gluconate are the standard first-line treatments for iron deficiency. NICE recommends 100-200mg of elemental iron daily, taken on an empty stomach with vitamin C for optimal absorption. Side effects (nausea, constipation, dark stools) are common but can be managed by taking supplements with food, trying alternative formulations, or using alternate-day dosing.
• Alternate-day dosing: Recent research suggests that taking iron supplements every other day may be better absorbed than daily dosing, due to hepcidin elevation that occurs after iron intake.
• Intravenous iron: For patients who cannot tolerate oral iron, have severe deficiency, or have malabsorption conditions, IV iron infusions (such as ferric carboxymaltose) provide rapid repletion and are increasingly used in the NHS.

Addressing Underlying Causes

• Investigate and treat blood loss: If iron deficiency is not explained by diet or menstruation, gastrointestinal investigation is essential. Coeliac serology should be checked in all cases of unexplained iron deficiency.
• Manage heavy periods: If menstrual blood loss is the cause, hormonal treatments (combined pill, hormonal coil/Mirena) can significantly reduce bleeding and iron loss.

When Should You Get Tested?

Consider iron testing if you experience:

• Persistent fatigue or low energy that does not improve with rest
• Breathlessness on exertion or climbing stairs
• Pale skin, pale nail beds, or pale inner eyelids
• Heart palpitations or rapid heartbeat
• Cold hands and feet
• Brittle nails, hair loss, or mouth ulcers
• Restless legs, especially at night
• Heavy menstrual periods
• You follow a vegetarian or vegan diet
• You are pregnant or planning pregnancy
• You have a family history of haemochromatosis
• Unexplained joint pain or elevated liver enzymes (possible iron overload)

Which Lola Health Tests Include Iron?

Iron is one of the most important biomarkers we measure at Lola Health and is included in several of our comprehensive panels:

• Peak Insights — Our most extensive health panel, including a complete iron profile (serum iron, ferritin, TIBC, transferrin saturation) alongside a full blood count and over 50 other biomarkers.
• Vital Check — A detailed wellness assessment that includes key iron markers to help you understand your iron status and energy levels.
• Core Health — An essential health check covering foundational biomarkers including iron and ferritin for a clear picture of your overall health.

All Lola Health tests use venous blood draws performed by qualified phlebotomists for medical-grade accuracy. Results are reviewed by GP-certified professionals and delivered with personalised health recommendations.