Iron and ferritin testing — symptoms, numbers, and what to do about low results

What iron does in the body

Iron is essential for several biological processes: making haemoglobin (which carries oxygen in red blood cells), supporting muscle function (myoglobin), supporting brain function (neurotransmitter synthesis, particularly dopamine), and supporting immune function. The body has roughly 3–4 grams of total iron, with about two-thirds in haemoglobin and the rest split between muscle, ferritin storage, and enzyme systems.

When iron intake doesn't match losses, stores deplete in a specific order: ferritin first (storage iron), then transport iron, then haemoglobin. By the time haemoglobin drops enough to be classed as anaemia, ferritin has typically been low for months.

The iron studies panel

A full panel includes:

• Ferritin. The storage marker. The most reliable single indicator of total body iron stores in non-acute scenarios.
• Serum iron. Iron currently circulating. Fluctuates with recent meals and time of day; less reliable as a stand-alone marker.
• TIBC (total iron binding capacity). A measure of transferrin's capacity to carry iron. Rises in iron deficiency (the body upregulates transferrin to capture available iron).
• Transferrin saturation. Serum iron divided by TIBC. Reflects how 'full' the transport system is. Low in iron deficiency.
• Full blood count (FBC). Includes haemoglobin (Hb), mean corpuscular volume (MCV — small red cells suggest iron deficiency), and red cell distribution width.

For most non-acute scenarios, ferritin alone is the most informative test. The full panel is useful when ferritin is borderline, when inflammation is suspected (ferritin is an acute-phase reactant and rises with inflammation, masking deficiency), or when planning treatment.

Iron deficiency vs iron deficiency anaemia

These are not the same thing:

• Iron deficiency anaemia (IDA). Low iron stores AND low haemoglobin. The classic 'anaemia' diagnosis. Usually picked up by standard blood tests because haemoglobin is included.
• Iron deficiency without anaemia (IDA-). Low iron stores, normal haemoglobin. Causes meaningful symptoms (fatigue, hair shedding, restless legs, reduced exercise tolerance, breathlessness on exertion) even though Hb is 'normal'.

NHS pathways often only treat once haemoglobin is low. This leaves a significant number of patients (mostly women) symptomatic with low ferritin but 'normal' bloods. Private testing and targeted treatment makes a difference for this group.

Reference ranges — normal vs optimal

Standard UK lab reference range for ferritin is typically 13–300 ng/mL for women and 30–400 ng/mL for men (varies by lab). This means a result of 14 ng/mL technically falls 'within range'.

Functional and specialist references often use higher floors:

• Many haematology and women's health specialists target ferritin >30 ng/mL (some prefer >50) for asymptomatic patients.
• For patients with symptoms compatible with iron deficiency (fatigue, hair shedding, restless legs), target ferritin is often 50–100 ng/mL.
• For endurance athletes, some sports physicians target ferritin 80–100+ ng/mL.
• For patients with restless legs syndrome, ferritin >75 ng/mL is the typical neurology target.

The 'normal range vs optimal' debate matters in practice because telling a symptomatic woman with ferritin 18 ng/mL that she's 'normal' often misses a correctable cause.

Symptoms of low iron

Iron deficiency, with or without anaemia, can produce:

• Fatigue, especially exertional fatigue.
• Breathlessness on exertion.
• Hair shedding (telogen effluvium-pattern).
• Restless legs, particularly at rest in evening / at night.
• Reduced exercise tolerance, slower recovery.
• Pale skin, especially noticed in conjunctivae (the inner lower eyelid) and palms.
• Brittle nails, spoon-shaped nails (koilonychia in severe cases).
• Pica (unusual cravings, especially for ice).
• Reduced concentration and memory ('iron-deficient brain fog').
• Reduced mood and motivation.
• Headaches.
• Cold intolerance.
• In children: developmental delay, behavioural issues.

Who's at highest risk

• Women of reproductive age. Menstrual blood loss is the most common cause of iron deficiency in the UK. Heavy periods especially.
• Pregnant women. Iron demands roughly double in pregnancy.
• Breastfeeding women. Some additional iron demand.
• Vegans and vegetarians. Plant-source non-haem iron is less bioavailable than haem iron from animal foods.
• Endurance athletes. Foot-strike haemolysis (runners), sweat losses, increased red cell turnover.
• Anyone with malabsorption. Coeliac disease, inflammatory bowel disease, bariatric surgery patients (especially Roux-en-Y).
• Older adults. Reduced gastric acid affects iron absorption; also possible occult GI blood loss requiring investigation.
• People with chronic kidney disease. Multiple mechanisms of iron deficiency.
• Anyone with GI blood loss (often silent) — ulcers, polyps, cancer, NSAID use.
• Patients on rapid weight loss including GLP-1 medication. Reduced food intake compounds with other risk factors. See our hair loss on Mounjaro guide and protein and nutrition guide.

The 'is there GI blood loss?' question

For men of any age and postmenopausal women with iron deficiency, the question 'where is the blood going?' becomes important — because the most likely answer is GI loss (often silent), and that can include early bowel cancer. NICE guidance recommends investigation (often endoscopy) in these groups when iron deficiency is found.

For premenopausal women with heavy periods and otherwise unremarkable history, GI investigation isn't routine first-line — menstrual loss is the working assumption — but persistent deficiency despite replacement may warrant looking further.

Treatment options

Oral iron. The first-line for most patients. Options:

• Ferrous sulphate, fumarate, gluconate. Standard NHS choices. Effective but commonly cause GI side effects. Typical dose: 200 mg ferrous sulphate one to three times daily, with re-test at 3 months.
• Ferrous bisglycinate. Better tolerated; often preferred in pharmacist-led services. Lower elemental iron per tablet but proportionally better absorbed and fewer GI effects.
• Sucrosomial iron. Newer formulation; well tolerated, well absorbed. More expensive.

Practical tips for oral iron:

• Take with vitamin C (orange juice, supplement) to enhance absorption.
• Avoid taking with tea, coffee, dairy, or calcium supplements within 2 hours — these reduce absorption.
• Alternate-day dosing (rather than daily) is now considered more efficient for absorption and produces fewer side effects.
• Persistence matters: 3–6 months of consistent dosing is typical for full replacement.
• Re-test ferritin at 3 months to confirm response.

IV iron infusion. Indicated for: severe deficiency requiring rapid replacement, ongoing blood loss outpacing oral replacement, intolerance to oral iron, malabsorption, chronic kidney disease, certain pre-surgical preparation. Single-session infusions (ferric carboxymaltose, iron isomaltoside) replace deficits in one or two visits.

Dietary iron — useful but rarely sufficient for deficiency

Once you're iron-deficient, diet alone usually isn't enough to restore stores in a reasonable timeframe. Diet matters for maintenance after replacement and for preventing recurrence:

• Haem iron (from meat, especially red meat, liver, fish) is well-absorbed (15–35%).
• Non-haem iron (from plants, fortified cereals, eggs) is less well-absorbed (2–20%) but absorption improves with vitamin C and decreases with tea/coffee.
• For vegetarians and vegans: emphasis on iron-rich plant foods (legumes, dark leafy greens, fortified grains, tofu, pumpkin seeds), paired with vitamin C, and avoiding tea/coffee at meals.

How iron deficiency presents alongside rapid weight loss

Rapid weight loss — from bariatric surgery, very-low-calorie diets, or GLP-1 medication — commonly worsens iron deficiency. Three reasons:

• Reduced food intake overall.
• Reduced protein and iron-rich food specifically.
• Sometimes reduced gastric acid affecting absorption.

For patients on Mounjaro, Wegovy, or post-bariatric, ferritin checks at baseline and at 6-month intervals are sensible. See our protein guide, hair loss guide, and post-bariatric Mounjaro guide for context.

Test interpretation — a few pitfalls

• Inflammation raises ferritin artefactually. Recent infection, autoimmune flare, or chronic inflammatory disease can mask iron deficiency by elevating ferritin. CRP alongside ferritin helps detect this.
• Recent iron supplementation skews recent serum iron. Test before supplementation or after a brief washout for baseline.
• Liver disease affects ferritin interpretation. Ferritin rises with liver inflammation.
• Hereditary haemochromatosis (iron overload) presents with high ferritin and high transferrin saturation — different problem with different treatment (venesection).

What we typically include in an iron check

Standard panel:

• Ferritin
• Serum iron
• TIBC
• Transferrin saturation
• Full blood count
• Optional: CRP if recent inflammation suspected

How this fits with other testing

Iron testing often goes alongside thyroid testing and vitamin D testing for non-specific fatigue presentations. For an overall blood test overview see our private blood test guide. For women near menopause, see menopause hormone testing.

If results are abnormal

Your pharmacist will annotate results with context. Common pathways:

• Iron deficiency anaemia (low ferritin, low Hb). Oral iron replacement, dietary advice, investigation of cause if not obvious, 3-month re-test.
• Iron deficiency without anaemia (low ferritin, normal Hb). Oral iron replacement, dietary advice, 3-month re-test.
• Concerning patterns (very low ferritin, microcytic anaemia in unexpected demographics): GP review and possible GI investigation.
• High ferritin with high transferrin saturation: screen for haemochromatosis.

The Leicester clinic context

We process iron studies through UKAS-accredited labs with 24–48 hour turnaround. Pharmacist-reviewed results with clear recommendations. The Independent Prescriber on-site means we can also dispense iron replacement therapy same-day where appropriate — including better-tolerated formulations like ferrous bisglycinate.

The next step

If you suspect iron deficiency — fatigue, hair shedding, restless legs, breathlessness, heavy periods — a same-day phlebotomy slot gets the picture clear. Combined with thyroid and vitamin D testing if fatigue is the leading symptom, you'll usually have actionable answers within 48 hours.