Ferritin and Fatigue: The Blood Test Your GP Might Not Be Running

Fatigue is one of the most common reasons people visit their GP, and one of the hardest to investigate. The list of potential causes is long, and standard blood tests do not always capture the problem. One frequently overlooked marker is ferritin — a measure of your iron stores that can explain persistent tiredness even when your haemoglobin is completely normal.

What Is Ferritin?

Ferritin is a protein that stores iron inside your cells. When your body needs iron — to make haemoglobin, support enzyme function, or fuel immune cells — it draws on these ferritin stores. Your blood ferritin level reflects how much iron you have in reserve.

The reference range for ferritin varies between laboratories, but most use a lower limit of around 13–15 mcg/L for women and 30 mcg/L for men. However, these thresholds define the point at which stores are essentially exhausted. A growing body of evidence suggests that symptoms of iron depletion — particularly fatigue — can occur at ferritin levels well above the traditional lower limit.

The Evidence for Ferritin and Fatigue

A comprehensive review on iron deficiency without anaemia concluded that ferritin below 30 mcg/L is the appropriate cut-off for identifying clinically significant iron depletion in adults, and that iron supplementation improves fatigue in this group even when haemoglobin is normal [Clenin, 2017]. This is a crucial distinction: you do not need to be anaemic to be iron deficient, and you do not need to be anaemic for that deficiency to affect how you feel.

Several randomised controlled trials have demonstrated that iron supplementation in non-anaemic women with low ferritin significantly reduces fatigue scores compared with placebo. A 2012 trial of 198 menstruating women found that those given oral iron for 12 weeks reported significantly less fatigue than the placebo group, with the greatest benefit seen when ferritin was below 50 mcg/L [Vaucher et al., 2012]. Some clinicians now use this as a functional threshold for investigating fatigue-related symptoms.

Why Ferritin Is Often Missed

When you see your GP with fatigue, the initial blood tests typically include a full blood count (FBC) and sometimes basic biochemistry. The FBC checks your haemoglobin level, which tells you whether you are anaemic. But haemoglobin is the last marker to fall in iron deficiency — by the time it drops, your stores have been empty for some time.

Unless your GP specifically requests a ferritin level, the early and intermediate stages of iron depletion will not be detected. This means you could be told your blood tests are "all normal" despite having genuinely depleted iron stores and symptoms that iron replacement would improve.

Who Is Most at Risk?

Certain groups are particularly susceptible to low ferritin:

• Premenopausal women, especially those with heavy periods

• Pregnant and postpartum women

• Vegetarians and vegans (plant-based iron is less readily absorbed)

• Endurance athletes (running in particular increases iron loss)

• Regular blood donors

• People with coeliac disease or inflammatory bowel disease

• Adolescents during rapid growth periods

If you fall into one of these groups and experience persistent fatigue, checking ferritin should be a priority.

Dietary Iron: What You Can Do Before Supplementation

Before reaching for supplements, it is worth understanding how dietary iron works. There are two forms: haem iron (found in red meat, poultry, and fish) and non-haem iron (found in legumes, dark green vegetables, nuts, and fortified cereals). Haem iron is absorbed two to three times more efficiently than non-haem iron, which is why vegetarians and vegans are at higher risk of depletion even with adequate intake on paper.

A practical tip: consuming vitamin C alongside iron-rich foods significantly improves absorption of non-haem iron. A glass of orange juice with a meal, or adding peppers and tomatoes to a lentil dish, can make a meaningful difference. Conversely, tea and coffee consumed with meals reduce absorption, so spacing these out can help.

That said, dietary changes alone are often insufficient to correct established iron depletion — particularly when ferritin has fallen below 30 mcg/L. In these cases, supplementation under medical guidance is usually needed.

Interpreting Your Ferritin Result

Ferritin interpretation is not always straightforward. Because ferritin is also an acute-phase reactant, it rises during inflammation, infection, and chronic disease. This means a "normal" ferritin in someone with an inflammatory condition does not necessarily rule out iron deficiency.

In practice, this means:

• Ferritin below 30 mcg/L is consistent with iron depletion

• Ferritin below 50 mcg/L in the context of fatigue may warrant a trial of iron supplementation

• Ferritin below 100 mcg/L in someone with chronic kidney disease, heart failure, or inflammatory bowel disease may still indicate insufficient iron stores

• A raised CRP alongside ferritin helps identify whether inflammation is masking the true picture

Your GP or the doctor interpreting your results should always consider ferritin alongside the clinical context — not in isolation.

When to See Your GP

If you have been experiencing fatigue for more than four weeks — particularly if it is affecting your ability to work, exercise, or function normally — ask your GP for blood tests that include ferritin as well as a full blood count. If ferritin is low, your GP will want to identify the cause. In premenopausal women, menstrual loss is the most common explanation, but in men and postmenopausal women, further investigation is often needed to rule out gastrointestinal blood loss or malabsorption.

Iron supplementation should be guided by your results and monitored with repeat testing after 8–12 weeks to ensure stores are replenishing.

How Brooksby Medical Can Help

While your GP should always be your first port of call for persistent fatigue, getting a comprehensive iron panel on the NHS is not always straightforward. A standard 10-minute consultation often focuses on the full blood count, and requesting additional markers like ferritin, transferrin saturation, and TIBC may require a second appointment or a specific clinical indication. If you are struggling to get the answers you need, Brooksby Medical can help bridge that gap.

Our Iron Profile Blood Test measures ferritin alongside serum iron, TIBC, and transferrin saturation — the full picture needed to properly assess your iron stores. If fatigue is your primary concern, the Nutrients and Energy Profile covers ferritin alongside thyroid function, vitamin D, B12, and folate — the key markers that commonly contribute to tiredness. Every result comes with a doctor-written report from Dr James Coleman that explains what your levels mean in clinical context, not just whether they fall within the laboratory reference range.

If previous blood tests have come back “normal” but you are still exhausted, checking your ferritin may be the missing piece. Order your Iron Profile Blood Test here.

References

1. Clenin GE. The treatment of iron deficiency without anaemia (in otherwise healthy persons). Swiss Med Wkly. 2017;147:w14434

2. Vaucher P, et al. Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial. CMAJ. 2012;184(11):1247-1254

3. Soppi ET. Iron deficiency without anemia — a clinical challenge. Clin Case Rep. 2018;6(6):1082-1086

Written by Dr James Coleman, GP and founder of Brooksby Medical. Dr Coleman is a practising General Practitioner who founded Brooksby Medical to give patients direct access to the blood tests and clinical interpretation they need, without waiting lists.

Medically reviewed: March 2026 | Next review due: March 2027

Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Blood test results should always be interpreted by a qualified healthcare professional in the context of your individual symptoms, medical history, and clinical picture. If you have concerns about your health, please consult your GP.