If You're Always Tired, Ask for This Blood Test

If you have been told your blood tests are "fine" but still feel exhausted, flat and cold, you may not have had the right tests. Non-anaemic iron deficiency, where iron stores are low but haemoglobin remains within the normal range, is one of the most underdiagnosed causes of persistent fatigue in women. Its symptoms overlap with those commonly attributed to stress, hormones or ageing.

A November 2025 meta-analysis published in Neuroscience and Biobehavioural Reviews pooled 16 randomised trials involving 1,408 non-anaemic children, adolescents and menstruating adults with biochemically confirmed iron deficiency. Iron supplementation significantly improved fatigue, physical well-being and symptoms of anxiety, with signals of benefit for depression and cognitive performance (Fiani et al., 2025). Importantly, these benefits were seen specifically in people with confirmed iron deficiency, not in the general population. This is a targeted intervention, not a blanket recommendation.

Ferritin, the storage form of iron, is the key marker to know. Many contemporary guidelines support a ferritin level below approximately 30 μg/L as evidence of iron deficiency in otherwise healthy adults. A landmark 2025 multinational study published in The Lancet Global Health, using physiological markers across 12 countries, found that iron-restricted red blood cell production begins in non-pregnant women when ferritin falls below 24.8 μg/L (Addo et al., 2025). These findings suggest that current diagnostic thresholds may underestimate iron deficiency in some women, although clinical guidelines continue to evolve (Al-Naseem et al., 2021).

Because ferritin also rises during inflammation or infection, clinicians sometimes interpret it alongside C-reactive protein (CRP) and other iron studies to avoid missing iron deficiency that may be masked by an inflammatory response.

Why this gets missed

The symptom profile overlaps with almost everything else. Persistent tiredness, low mood, poor sleep, brain fog, low libido, hair thinning, breathlessness on stairs, and cold hands and feet are often attributed to work stress, hormones or simply "being busy". In some cases, symptoms are dismissed because haemoglobin remains normal or because it is assumed that treatment is only needed once anaemia develops. The evidence suggests we should look more closely.

Why this is genuinely fixable

Non-anaemic iron deficiency is one of the more readily treatable medical causes of fatigue when it is correctly identified. Many people experience meaningful improvement within around two to three months of appropriate treatment (Fiani et al., 2025).

Practical takeaway: symptoms to watch for

None of these symptoms is specific to iron deficiency, but several occurring together should prompt further assessment. If you have experienced two or more of the following for longer than a month, it is worth discussing them with your GP:

• Persistent fatigue not fully explained by poor sleep

• Low mood or anxiety that has gradually developed

• Hair thinning, brittle nails or unusual hair loss

• Cold hands and feet

• Restless legs at night

• Reduced libido or declining exercise tolerance

• Recurrent headaches or dizziness when standing

Best practice: ask for the full iron panel

Do not assume that "your full blood count is fine" means your iron status has been fully assessed. Ask whether your iron stores have also been measured. A useful assessment typically includes:

• Serum ferritin (ask for your actual number, not simply whether it is "in range")

• Transferrin saturation (to assess how much circulating iron is available for use)

• Full blood count for clinical context

Discuss the results with your GP. If your ferritin is below 30 μg/L and you have symptoms consistent with iron deficiency, ask whether a trial of iron supplementation is appropriate for you.

Avoid taking high-dose iron supplements without confirming deficiency first. Excess iron carries genuine risks, particularly for people with undiagnosed conditions such as haemochromatosis. Your GP may also investigate the underlying cause of iron deficiency, especially if you are not menstruating, experience very heavy menstrual bleeding, or have symptoms that could suggest gastrointestinal blood loss or malabsorption.

A reflection

When did you last see your own ferritin number? Knowing it is the first step. Acting on it, together with your GP, is the second.

References:

Fiani, D., Chahine, S., Zaboube, M., Solmi, M., Powers, J. M., & Calarge, C. (2025). Psychiatric and cognitive outcomes of iron supplementation in non-anemic children, adolescents, and menstruating adults: A meta-analysis and systematic review. Neuroscience and Biobehavioral Reviews, 178, 106372. 

Addo, O. Y., Mei, Z., Jefferds, M. E. D., Jenkins, M., Flores-Ayala, R., Williams, A. M., Young, M. F., Luo, H., Ko, Y. A., Papassotiriou, I., Palmieri, M., Mesarina, K., Bhutta, Z., Suchdev, P. S., & Brittenham, G. M. (2025). Physiologically based serum ferritin thresholds for iron deficiency among women and children from Africa, Asia, Europe, and central America: A multinational comparative study. The Lancet Global Health, 13(5), e831-e842. 

Al-Naseem, A., Sallam, A., Choudhury, S., & Thachil, J. (2021). Iron deficiency without anaemia: A diagnosis that matters. Clinical Medicine, 21(2), 107-113.