Iron Deficiency vs Iron Deficiency Anaemia: What's the Difference?

You're exhausted. You've been exhausted for months. You mention it to your GP, who orders a full blood count. The results come back — haemoglobin normal. "Your bloods are fine," they say. But nobody checked your ferritin, and you're far from fine.

This scenario plays out thousands of times a week across the UK. The reason? A fundamental misunderstanding of the difference between iron deficiency and iron deficiency anaemia. They're related — but they're not the same thing, and the distinction matters enormously for getting the right diagnosis and treatment.

Iron Deficiency vs Anaemia: The Key Difference

Iron deficiency means your body's iron stores are depleted. You don't have enough iron to meet your needs, but your body is still managing to produce adequate haemoglobin — the oxygen-carrying protein in your red blood cells. Think of it as running on reserves.

Iron deficiency anaemia is the next stage. Your iron stores have been depleted for so long that your body can no longer produce enough haemoglobin, and your red blood cells become smaller, paler, and less effective at carrying oxygen. This is when anaemia shows up on a full blood count.

The critical point: you can be iron deficient for months or years before developing anaemia. During this time, you may feel terrible — fatigued, foggy, breathless on exertion — but standard blood tests that only check haemoglobin will show "normal" results. Your body is compensating, but at a cost.

Practical takeaway: If your haemoglobin is normal but you have symptoms of iron deficiency, the problem isn't that you're fine — it's that the wrong test was ordered. Ferritin is the test you need.

Symptoms of Iron Deficiency

The symptoms of iron deficiency and iron deficiency anaemia overlap significantly. The difference is usually one of severity — iron deficiency causes milder versions of the same problems that become more pronounced as anaemia develops.

Common symptoms at both stages

• Fatigue and exhaustion — a bone-deep tiredness that sleep doesn't fix
• Breathlessness — particularly on exertion, such as climbing stairs
• Difficulty concentrating — brain fog, poor memory, trouble focusing
• Pale skin — particularly noticeable on the inner lower eyelids and nail beds
• Heart palpitations — your heart works harder to compensate for reduced oxygen delivery
• Restless legs — an urge to move your legs, especially at rest or at night
• Headaches and dizziness

Symptoms more common in advanced deficiency or anaemia

• Cold hands and feet
• Brittle or spoon-shaped nails (koilonychia)
• Sore or swollen tongue (glossitis)
• Cravings for non-food items — ice, dirt, or starch (pica)
• Hair thinning or increased shedding

Practical takeaway: Don't wait for anaemia to develop before seeking help. Even mild iron deficiency can significantly impact your quality of life, and early treatment is much faster than correcting established anaemia.

Who's at Risk?

Iron deficiency is the most common nutritional deficiency worldwide, and the UK is no exception. Groups at highest risk include:

• Women of reproductive age — menstrual blood loss is the most common cause of iron deficiency in pre-menopausal women
• Pregnant women — iron requirements increase dramatically during pregnancy
• Vegetarians and vegans — plant-based (non-haem) iron is absorbed less efficiently than haem iron from animal sources
• Endurance athletes — intense exercise increases iron losses through sweat and gastrointestinal bleeding
• People with gastrointestinal conditions — coeliac disease, Crohn's disease, and ulcerative colitis impair absorption
• Regular blood donors — each donation removes approximately 250 mg of iron
• Older adults — reduced intake and increased prevalence of conditions causing chronic blood loss
• People taking PPIs or antacids — these reduce the stomach acid needed for iron absorption

The Blood Tests You Need

A full picture of iron status requires more than just a haemoglobin check. Here are the key markers:

Ferritin is the single most important test for iron deficiency. It measures your body's iron stores. A low ferritin virtually always means iron deficiency, even if haemoglobin is normal. However, ferritin is also an acute-phase reactant — it rises during infection, inflammation, and liver disease — so a "normal" ferritin doesn't always rule out deficiency in those contexts.

Serum iron measures circulating iron at the time of the test. It fluctuates throughout the day, so it's less reliable alone.

TIBC (total iron-binding capacity) measures available transferrin — the protein that transports iron. When stores are low, TIBC rises as your body produces more transferrin to capture whatever iron is available.

Transferrin saturation is the percentage of transferrin currently carrying iron. Low saturation confirms insufficient iron supply.

Full blood count (FBC) reveals whether anaemia has developed. In iron deficiency anaemia, you'll see low haemoglobin and low MCV (smaller red blood cells).

Understanding Your Results

Marker	Normal Range	Iron Deficiency	Iron Deficiency Anaemia
Ferritin	30–300 µg/L (men), 30–150 µg/L (women)	Low (below 30 µg/L)	Very low (often below 15 µg/L)
Serum iron	10–30 µmol/L	Low	Low
TIBC	45–81 µmol/L	High	High
Transferrin saturation	20–50%	Low (below 20%)	Very low (below 16%)
Haemoglobin	130–170 g/L (men), 120–150 g/L (women)	Normal	Low
MCV	80–100 fL	Normal or low-normal	Low (microcytic)

Practical takeaway: Many labs consider ferritin "normal" down to 10–15 µg/L. However, symptoms of iron deficiency commonly appear at levels below 30 µg/L, and many specialists advocate for maintaining ferritin above 50 µg/L for optimal energy and wellbeing.

Causes of Iron Deficiency

Understanding why you're iron deficient is just as important as treating it. The main categories are:

Not enough iron coming in

• Inadequate dietary intake — restrictive diets, vegan/vegetarian diets without planning, or disordered eating
• Poor absorption — coeliac disease, inflammatory bowel disease, gastric bypass, or medications that reduce stomach acid

Too much iron going out

• Heavy menstrual periods — the most common cause in pre-menopausal women
• Gastrointestinal blood loss — ulcers, bowel polyps, bowel cancer, or regular NSAID use
• Regular blood donation

Increased demand

• Pregnancy and breastfeeding
• Rapid growth (adolescents)
• Intense athletic training

Important: In men and post-menopausal women, iron deficiency should always prompt investigation into gastrointestinal blood loss, as it can be the first sign of bowel cancer.

Treatment

Dietary changes

Increasing iron-rich foods helps prevent deficiency and supports recovery:

• Haem iron (best absorbed): red meat, liver, shellfish, sardines
• Non-haem iron (less well absorbed but still valuable): lentils, chickpeas, beans, tofu, dark leafy greens, fortified cereals, dried apricots
• Enhance absorption: Eat iron-rich foods with vitamin C (citrus fruit, peppers, tomatoes) to significantly boost non-haem iron uptake
• Reduce absorption blockers: Tea, coffee, calcium supplements, and high-fibre cereals can inhibit iron absorption when consumed at the same time as iron-rich foods

Iron supplements

When diet alone isn't enough — or when deficiency is already established — supplementation is necessary. The most commonly prescribed form in the UK is ferrous sulphate (200 mg tablets, usually taken two to three times daily).

Tips for better results:

• Take on an empty stomach if tolerable, with vitamin C to boost absorption
• Avoid taking within two hours of tea, coffee, dairy, or antacids
• If daily iron causes side effects (constipation, nausea), alternate-day dosing may improve absorption while reducing discomfort

Ferritin should be rechecked after 8–12 weeks of supplementation. Continue for 3–6 months after ferritin normalises to fully replenish stores.

When to See a Doctor

Seek medical advice if:

• You have persistent symptoms of iron deficiency despite dietary changes
• Your ferritin is below 15 µg/L
• You're a man or post-menopausal woman with iron deficiency (gastrointestinal investigation is usually warranted)
• You have heavy menstrual bleeding that you suspect is contributing
• Your haemoglobin is below the normal range (iron deficiency anaemia)
• You've been supplementing for 8–12 weeks with no improvement in ferritin
• You have a gastrointestinal condition that may be affecting absorption

Iron deficiency is treatable, but identifying the underlying cause is essential. Topping up iron stores without understanding why they're depleted in the first place means the problem will keep coming back.

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