Iron is essential for the production of haemoglobin — the protein in red blood cells that carries oxygen from the lungs to every tissue in the body. When iron stores fall, haemoglobin production declines, oxygen delivery is impaired, and the body's cells begin to function suboptimally. The result is a constellation of symptoms — fatigue, breathlessness, poor concentration, hair loss, and palpitations — that are among the most common reasons patients seek medical attention, yet are frequently attributed to stress, overwork, or other conditions before a blood test is performed.
Iron deficiency anaemia (IDA) is the most common nutritional deficiency worldwide, affecting approximately 1.2 billion people[1]. A UK study of over 33,000 private health check participants found that almost 1 in 10 women were anaemic and nearly 1 in 3 had absolute iron deficiency — with the highest rates in women of reproductive age[5]. A private iron studies blood test at Victoria Medical returns results within 24 hours, with a doctor-reviewed written report explaining your result and a personalised treatment plan.
1. Iron Deficiency vs Iron Deficiency Anaemia: A Critical Distinction
Iron deficiency and iron deficiency anaemia are not the same condition. Iron deficiency — defined as low iron stores (serum ferritin below 30 ng/mL) — can cause significant symptoms even when haemoglobin remains within the normal range. This is known as iron deficiency without anaemia (IDWA), and it is at least twice as common as IDA itself[4]. Fatigue, brain fog, hair loss, restless legs syndrome, and exercise intolerance are all well-documented features of IDWA — yet many patients are told their blood tests are "normal" because only a full blood count (FBC) was requested, without ferritin.
A JAMA review by Auerbach et al. (2025) confirmed that in high-income countries, approximately 38% of non-pregnant women of reproductive age have iron deficiency without anaemia, and about 13% have iron deficiency anaemia[1]. This is why a comprehensive iron studies panel — including ferritin, serum iron, transferrin saturation, and TIBC — is essential for a complete assessment.
| Condition | Ferritin | Haemoglobin | Symptoms | Action Required |
|---|---|---|---|---|
| Iron deficiency without anaemia (IDWA) | < 30 ng/mL | Normal | Fatigue, hair loss, brain fog, restless legs — often significant | Iron supplementation; investigate cause |
| Iron deficiency anaemia (IDA) | < 30 ng/mL | Low (< 12 g/dL women; < 13 g/dL men) | All IDWA symptoms plus breathlessness, pallor, palpitations, exercise intolerance | Iron supplementation; investigate cause; consider IV iron if oral fails |
| Functional iron deficiency | Normal or high | Low | Fatigue, breathlessness — in chronic inflammatory conditions (IBD, CKD, heart failure) | Intravenous iron; treat underlying condition |
| Normal iron status | 30–300 ng/mL | Normal | None attributable to iron | No action required |
2. Symptoms of Iron Deficiency and Iron Deficiency Anaemia
A comprehensive symptom analysis by Özbilen et al. (2025) documented 41 distinct symptoms in women with iron deficiency, with the most common being weakness (87%), fatigue (82%), easy fatigability (79%), memory problems (72%), feeling cold (72%), and hair loss (70%). Critically, most of these symptoms were equally prevalent in women with iron deficiency without anaemia as in those with overt IDA — confirming that a normal haemoglobin does not exclude clinically significant iron deficiency.
Common symptoms of iron deficiency
- Persistent fatigue and weakness — the most common presenting complaint
- Breathlessness on exertion — even with mild activity
- Palpitations — awareness of the heartbeat at rest
- Poor concentration and brain fog — difficulty with memory and focus
- Hair loss — diffuse thinning, particularly in women
- Pale skin, pale inner eyelids, and pale nail beds
- Brittle or spoon-shaped nails (koilonychia)
- Restless legs syndrome — urge to move legs, particularly at night (32–40%)
- Pica — craving for non-food substances such as ice, clay, or starch (40–50%)
- Feeling cold — particularly in the hands and feet
- Headaches and dizziness
- Sore or smooth tongue (glossitis)
High-risk groups for iron deficiency in the UK
- Women of reproductive age — heavy menstrual bleeding is the most common cause
- Pregnant and breastfeeding women — iron requirements increase significantly
- Vegetarians and vegans — non-haem iron from plant sources is less well absorbed
- Frequent blood donors
- Patients with coeliac disease or inflammatory bowel disease
- Post-bariatric surgery patients — reduced iron absorption
- Older adults — reduced dietary intake and increased GI blood loss risk
- Patients on regular NSAIDs or aspirin — increased GI blood loss
- Athletes — increased iron losses through sweat and haemolysis
3. Blood Tests for Iron Deficiency: What Is Measured and Why
Diagnosing iron deficiency requires more than a full blood count. A full blood count (FBC) measures haemoglobin and red cell indices — including mean corpuscular volume (MCV), which falls in iron deficiency — but it cannot detect iron deficiency without anaemia. Serum ferritin is the most reliable single marker of iron stores and is the test recommended by the British Society for Haematology (BSH) and the British Society of Gastroenterology (BSG) for diagnosing iron deficiency[2].
| Test | What It Measures | Normal Range | In Iron Deficiency |
|---|---|---|---|
| Serum ferritin | Iron stores — the most sensitive marker of iron deficiency | 20–300 ng/mL (women); 30–400 ng/mL (men) | Low (< 30 ng/mL) — diagnostic of iron deficiency |
| Haemoglobin (Hb) | Oxygen-carrying capacity of red blood cells | > 12 g/dL (women); > 13 g/dL (men) | Low in IDA; normal in IDWA |
| MCV (mean corpuscular volume) | Average size of red blood cells | 80–100 fL | Low (microcytic) in IDA; may be normal in early deficiency |
| Serum iron | Iron circulating in the blood | 60–170 µg/dL | Low in iron deficiency |
| TIBC (total iron binding capacity) | Capacity of transferrin to bind iron | 250–370 µg/dL | High — transferrin increases to capture more iron |
| Transferrin saturation (TSAT) | Percentage of transferrin binding sites occupied by iron | 20–50% | Low (< 20%) — confirms functional iron deficiency |
| Reticulocyte haemoglobin content (CHr) | Iron available for red cell production | > 28 pg | Low — early marker of functional iron deficiency |
4. Common Causes of Iron Deficiency Anaemia
The BSG guidelines (Snook et al., 2021) emphasise that IDA is not a diagnosis in itself — it is a consequence of an underlying cause that must be identified and treated[2]. The most common causes are blood loss (menstrual or gastrointestinal), impaired absorption, and inadequate dietary intake. Approximately one-third of men and post-menopausal women with IDA have an underlying gastrointestinal pathology — including colorectal cancer — which is why unexplained IDA in these groups is an accepted indication for urgent secondary care referral in the UK.
| Category | Common Causes | Investigations |
|---|---|---|
| Blood loss — gynaecological | Heavy menstrual bleeding (most common cause in women of reproductive age), fibroids, endometriosis | Gynaecology review; pelvic ultrasound |
| Blood loss — gastrointestinal | Peptic ulcer, gastritis, colorectal cancer, angiodysplasia, inflammatory bowel disease, NSAID use | Bidirectional GI endoscopy (urgent in men and post-menopausal women) |
| Impaired absorption | Coeliac disease, atrophic gastritis, Helicobacter pylori infection, post-bariatric surgery, proton pump inhibitor use | Coeliac serology; H. pylori testing; gastroscopy |
| Inadequate dietary intake | Vegetarian/vegan diet, restrictive eating, poverty, elderly patients with poor appetite | Dietary assessment; nutritional supplementation |
| Increased demand | Pregnancy (iron requirements increase 3-fold), breastfeeding, rapid growth in adolescence | Iron supplementation; obstetric review |
| Chronic inflammatory conditions | Inflammatory bowel disease, chronic kidney disease, heart failure, cancer — functional iron deficiency | Transferrin saturation; specialist review; IV iron |
From Our Practice
"I see iron deficiency missed in two ways. The first is the patient who has a full blood count showing a normal haemoglobin — and is told their blood tests are normal — when in fact they have a ferritin of 8 ng/mL and have been exhausted for two years. The second is the patient who is given iron supplements without any investigation into why they are iron deficient. In a woman of reproductive age with heavy periods, the cause is usually clear. But in a post-menopausal woman or a man with no obvious source of blood loss, unexplained iron deficiency is a red flag for gastrointestinal pathology — and a gastroscopy and colonoscopy are indicated. I always ask: why is this patient iron deficient? The treatment is straightforward; finding the cause is the important part."
Dr George Xynopoulos
MD, MRCP, FACC — Consultant Physician & Cardiologist, Victoria Medical
Frequently Asked Questions
What is the difference between iron deficiency and iron deficiency anaemia?
Iron deficiency means your iron stores are low (ferritin below 30 ng/mL), but your haemoglobin may still be within the normal range. Iron deficiency anaemia means your iron stores are low and your haemoglobin has also fallen below normal (below 12 g/dL in women, below 13 g/dL in men). Both conditions cause symptoms — fatigue, hair loss, brain fog, and restless legs are common in iron deficiency without anaemia — and both require treatment.
Can I test for iron deficiency without a GP referral?
Yes. You can book a private iron studies blood test at Victoria Medical directly, without a GP referral. A comprehensive panel — including ferritin, serum iron, TIBC, and transferrin saturation — can be arranged alongside a full blood count. Results are available within 24 hours with a doctor-reviewed written report.
What ferritin level is considered iron deficient?
A ferritin below 30 ng/mL is the threshold used by the British Society for Haematology and the British Society of Gastroenterology to diagnose iron deficiency. However, ferritin is an acute-phase reactant — it rises with inflammation, infection, and liver disease — which means a normal or elevated ferritin does not exclude iron deficiency in patients with chronic inflammatory conditions. In these cases, transferrin saturation below 20% is used to confirm functional iron deficiency.
How long does it take to correct iron deficiency anaemia?
With oral iron supplementation (ferrous sulfate 200 mg twice daily), haemoglobin typically rises by 1–2 g/dL per month. Most patients notice an improvement in energy and symptoms within 2–4 weeks. However, iron stores (ferritin) take 3–6 months to fully replenish after haemoglobin has normalised — which is why treatment should continue for at least 3 months after the haemoglobin has returned to normal.
Is oral or intravenous iron better?
Oral iron (ferrous sulfate or ferrous fumarate) is first-line for most patients. Intravenous iron is indicated when oral iron is not tolerated (gastrointestinal side effects affect up to 30% of patients), when absorption is impaired (coeliac disease, post-bariatric surgery), in chronic inflammatory conditions (IBD, CKD, heart failure), during the second and third trimesters of pregnancy, and when rapid iron repletion is required.
Does iron deficiency cause hair loss?
Yes. Hair loss — typically diffuse thinning rather than patchy alopecia — is a well-documented feature of iron deficiency, occurring in approximately 70% of women with iron deficiency in one comprehensive symptom study. The mechanism is that iron is required for the proliferation of hair follicle cells. Hair loss from iron deficiency typically improves within 3–6 months of successful treatment, though full recovery may take up to 12 months.
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Vitamin D Deficiency: Symptoms, Testing, and Treatment
Iron deficiency and vitamin D deficiency frequently co-exist. Dr Xynopoulos explains the symptoms of vitamin D deficiency, the NICE thresholds, and how to treat deficiency effectively.
Private Health Check: What Is Included and Is It Worth It?
A comprehensive private health check includes iron studies as a standard component. Dr Xynopoulos explains what is included in each package and who benefits most.
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References
- [1] Auerbach M, Gafter-Gvili A, Macdougall IC. Iron Deficiency in Adults: A Review. JAMA. 2025;333(4):323–334. https://consensus.app/papers/details/3a412162a4ec5c8db683f2173f0fae64/
- [2] Snook J, Bhala N, Beales ILP, et al. British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults. Gut. 2021;70(11):2030–2051. https://consensus.app/papers/details/8a07ad1458ea5ba18fc9476d77b03a84/
- [3] Kumar A, Brookes MJ. Iron Deficiency Anaemia: Pathophysiology, Assessment, Practical Management. BMJ Open Gastroenterol. 2022;9(1):e000759. https://consensus.app/papers/details/b1b74041bf525ed5bb04329475bc0da0/
- [4] Al-Naseem A, Sallam A, Choudhury S, Thachil J. Iron deficiency without anaemia: a diagnosis that matters. Clin Med. 2021;21(2):107–113. https://consensus.app/papers/details/c1ae34d9da825ea6be4b3f38017a59c8/
- [5] Irvine A, Watt C, Kurth MJ, et al. Ironically unwell: anaemia and iron deficiency among health-aware adults in the UK. Front Nutr. 2025;12:1567890. https://consensus.app/papers/details/51796fd41f7d58149023db4059a41757/
- [6] Iolascon A, Andolfo I, Russo R, et al. Recommendations for diagnosis, treatment, and prevention of iron deficiency and iron deficiency anemia. HemaSphere. 2024;8(7):e70. https://consensus.app/papers/details/7e0668d3c3bc5a258aca817afd1d2cef/
Dr George Xynopoulos
MD, MRCP, FACC — Consultant Physician & Cardiologist
Dr Xynopoulos is a Consultant Physician and Cardiologist at Victoria Medical, 170 Vauxhall Bridge Road, London SW1V 1DX. He provides comprehensive blood testing — including iron studies, ferritin, and full blood count panels — with same-day results and a doctor-reviewed written report.
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