Iron deficiency without anaemia (abbreviated IDNA in the haematology literature) is common, and Australian prescribing guidance describes it as under-recognised and undertreated (Balendran and Forsyth, Australian Prescriber 2021;44(6):193-6). How common iron deficiency is depends on the ferritin threshold used. In a 2025 study of apparently healthy non-pregnant women aged 15 to 49 in 12 countries, 20.1% were iron deficient at the WHO threshold of ferritin below 15 ug/L, and 36.0% using physiologically based thresholds, which pooled at 24.8 ug/L (Addo et al., Lancet Global Health 2025). It has been associated with fatigue, reduced exercise performance, difficulty concentrating and irritability (Balendran and Forsyth, Australian Prescriber 2021;44(6):193-6), all while haemoglobin sits above the anaemia threshold, so a haemoglobin check alone will not pick it up.
The blood tests that find it are routine iron studies. The gap is in how often they are ordered, and what they are read against.
The stages of iron deficiency
Iron deficiency moves through stages, and anaemia is the last one.
IDNA is the term used for Stages 1 and 2: ferritin low, haemoglobin still normal.
A 2025 Australian consensus statement describes the effects of iron deficiency occurring long before anaemia develops (HOW Collaborative, Internal Medicine Journal 2025).
Haemoglobin, the last marker to drop
Your body prioritises haemoglobin. When iron stores start running low, a cascade of hormonal and metabolic adjustments preserves red blood cell production at the expense of almost everything else. Iron gets pulled from ferritin stores, iron absorption upregulates, iron utilisation in non-essential tissues downregulates.
By the time haemoglobin falls, iron deficiency has reached its most advanced stage.
A normal haemoglobin shows that your body's compensation is working.
The IDNA symptom pattern
The symptoms of iron deficiency without anaemia overlap with those of iron deficiency anaemia, and often come on more gradually:
- Fatigue that sleep does not relieve, the hallmark
- Brain fog and difficulty concentrating, often worse in the afternoon
- Exercise intolerance, especially endurance performance, maximal oxygen uptake (VO₂max), and recovery
- Restless legs at night, which has been associated with iron deficiency without anaemia
- Hair shedding in the shower or brush, usually diffuse
- Cold hands and feet, especially in the evening
- Heart palpitations on exertion or on standing
- Mood disturbance: irritability, low affect, anxiety spikes
- Brittle nails: vertical ridges and lateral splits
- Pica: craving ice (pagophagia), clay, starch, or unusual textures
If several of these are familiar and you menstruate, iron deficiency is worth ruling out, whatever your haemoglobin says.
Guidelines versus clinical practice
The 2020 World Health Organization (WHO) ferritin guideline and Australian Prescriber's 2021 guidance both use ferritin to diagnose iron deficiency, and the 2021 Anaesthesia review I led argued that women with "normal" results should still be investigated for iron deficiency.
All three base the diagnosis of iron deficiency on ferritin. Evidence on treating it before anaemia develops is still limited, but Australian guidance says most people with confirmed iron deficiency can be given oral iron.
1. Reference ranges on laboratory reports
When a GP opens your results, ferritin is flagged as "normal" or "abnormal" against the laboratory's reference range, and a 2024 systematic review found those lower limits for women usually sit well below 30 ug/L (Truong et al., Lancet Haematology 2024). A ferritin of 22 prints as normal, even though Australian guidance treats anything below 30 ug/L as iron deficiency. The GP is reading the lab slip, and the lab slip is reading a range often set without excluding people at risk of iron deficiency.
2. Familiarity with haemoglobin
Anaemia is the most readily recognised effect of iron deficiency (Balendran and Forsyth, Australian Prescriber 2021;44(6):193-6), so haemoglobin is the result most people are used to reading. Changing that habit takes time.
3. Dismissal of fatigue in women
Fatigue in women can be put down to stress, anxiety or parenting before a full workup is done. The Anaesthesia review I led in 2021 pointed out that women are defined as anaemic at a lower haemoglobin than men.
4. Cheap, generic treatment
Oral iron is cheap and generic, and guidance reserves intravenous (IV) iron for specific situations, such as when oral iron has not worked (Balendran and Forsyth, Australian Prescriber 2021;44(6):193-6). No company has a reason to market this diagnosis.
Next steps with a normal haemoglobin
Step 1. The full iron panel
Request a full iron panel: ferritin, transferrin saturation, MCV, haemoglobin, and CRP (for context). If you only get haemoglobin, you are being assessed for anaemia alone.
Step 2. Diagnostic thresholds
For premenopausal women:
- Ferritin < 30 ug/L = iron deficiency (Balendran and Forsyth, Australian Prescriber 2021;44(6):193-6)
- Ferritin < 100 ug/L with transferrin saturation < 20% = iron deficiency when inflammation is present
- Transferrin saturation < 20% = corroborating evidence
- Elevated CRP means ferritin is inflated, interpret cautiously
Step 3. The words to use
Using the phrase "iron deficiency without anaemia" makes clear that you are asking about iron stores as well as anaemia.
Step 4. Treatment and cause
If your ferritin is under 30 and you have symptoms, discuss treatment and the cause with your GP. Australian guidance says most people with iron deficiency can be given oral iron (Balendran and Forsyth, Australian Prescriber 2021;44(6):193-6). Options:
- Oral iron is first line and cost effective, although gastrointestinal side effects such as nausea, stomach pain and diarrhoea can make it hard to keep taking
- Alternate-day oral iron absorbs a higher share of each dose with fewer gastrointestinal side effects, although in a six-month trial ferritin was no higher than with daily dosing at the same total dose
- Intravenous (IV) iron is used when oral iron has failed or is not tolerated, with malabsorption, and in some other conditions, and its use is limited by adverse effects including skin staining, low phosphate and, rarely, anaphylaxis
Step 5. The repeat test
Recheck ferritin 6 to 12 weeks into repletion. The goal is to replenish iron stores and find the cause (Balendran and Forsyth, Australian Prescriber 2021;44(6):193-6), confirmed on a repeat test.
Iron deficiency without anaemia (IDNA) as a recognised condition
- Iron deficiency without anaemia is a recognised condition in Australian prescribing guidance.
- Iron deficiency in women is often overlooked (Dugan et al., Anaesthesia 2021).
- Trials of intravenous iron in adults with iron deficiency and no anaemia show improvements in fatigue and physical function, although the certainty of that evidence is still limited (Dugan et al., Journal of Cachexia, Sarcopenia and Muscle 2022).
A ferritin of 22 with symptoms is iron deficiency under Australian guidance.
This article is educational and not medical advice. Discuss significant changes to supplementation or testing with a qualified clinician.
Related articles
Sources
The papers cited in this article.
- Addo OY, Mei Z, Jefferds MED, et al. 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 2025;13(5):e831-e842. doi:10.1016/S2214-109X(25)00009-9
- Balendran S, Forsyth C. Non-anaemic iron deficiency. Australian Prescriber 2021;44(6):193-196. doi:10.18773/austprescr.2021.052
- Dugan C, MacLean B, Cabolis K, et al. The misogyny of iron deficiency. Anaesthesia 2021;76(Suppl 4):56-62. doi:10.1111/anae.15432
- Dugan C, Cabolis K, Miles LF, Richards T. Systematic review and meta-analysis of intravenous iron therapy for adults with non-anaemic iron deficiency: an abridged Cochrane review. Journal of Cachexia, Sarcopenia and Muscle 2022;13(6):2637-2649. doi:10.1002/jcsm.13114
- Truong J, Naveed K, Beriault D, et al. The origin of ferritin reference intervals: a systematic review. The Lancet Haematology 2024;11(7):e530-e539. doi:10.1016/S2352-3026(24)00103-0