Iron deficiency without anemia (IDNA): the diagnosis GPs miss most often

If you have ever been told your iron is fine because your haemoglobin is in the normal range — this article is the one I wish your GP had read last week.

Iron deficiency without anemia (abbreviated IDNA in the hematology literature) is one of the most under-diagnosed conditions in primary care. It affects an estimated 15–25% of premenopausal women in high-income countries, and the prevalence is almost certainly higher in low-income settings. It causes meaningful fatigue, cognitive impairment, exercise intolerance, and mental health symptoms — all while the patient's haemoglobin sits comfortably above the anemia threshold, getting her cleared at every routine check.

The condition is not new. The diagnostic framework is not contested. But the clinical translation — from peer-reviewed journal into the 10-minute GP appointment — has failed, and millions of women are paying for that failure in exhausted afternoons and missed promotions.

What IDNA actually means

Iron deficiency is a process, not a single lab result. It has stages. Anemia is the last one.

Here is the physiological progression, in the order it happens in the body:

IDNA is the term used for any patient sitting at Stage 1, 2, or 3 — ferritin low, haemoglobin still normal.

The critical insight: the symptoms of iron deficiency do not wait for haemoglobin. They begin at Stage 1. Patients at Stage 2 and 3 are fully symptomatic. By the time anemia appears, the patient has typically been iron deficient for months to years.

Why haemoglobin is 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.

This is clinically clever. It also guarantees that by the time haemoglobin falls, the deficiency is severe.

Which means: a normal haemoglobin is evidence that your body's compensation is working — not evidence that your iron status is adequate.

The IDNA symptom pattern

The symptoms of IDNA overlap significantly with anemia of iron deficiency, but often present more insidiously. The classical cluster:

• Fatigue that is not relieved by sleep — the hallmark
• Brain fog and difficulty concentrating, often worse in the afternoon
• Exercise intolerance — especially endurance performance, VO₂max, and recovery
• Restless legs at night (one of the most specific IDNA signs)
• Hair shedding in the shower or brush — usually diffuse, not patchy
• 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 you have four or more of these and a menstrual cycle, the differential diagnosis should include IDNA — regardless of what your haemoglobin says.

Why modern guidelines catch it and clinical practice doesn't

The evidence base here is not ambiguous. The 2020 BMJ review, the WHO's updated 2020 guidance, the 2021 Anaesthesia paper our group contributed to, and multiple hematology society consensus statements all align on the same point:

Iron deficiency should be diagnosed on ferritin, not haemoglobin. Treatment indications begin well before the anemia threshold.

So why does practice lag so badly?

1. Lab reports are built around reference ranges, not thresholds

When a GP opens your results, ferritin is flagged as "normal" or "abnormal" based on the 15–200 µg/L range most labs still use. A ferritin of 22 prints as normal, even though every modern guideline considers it deficient. The GP is reading the lab slip, and the lab slip is reading a 1970s population.

2. Medical education hasn't caught up

Most GPs were trained on "haemoglobin = iron status" shorthand. Updating clinical habit requires continuing education, and iron is not considered a sexy topic in primary care training.

3. The patient cohort is disproportionately women

This matters. There is a documented tendency in primary care to attribute fatigue in premenopausal women to stress, anxiety, or motherhood before pursuing a thorough biomedical workup. The Anaesthesia paper I co-authored in 2021 argued explicitly that the diagnostic thresholds for iron deficiency have a sex-bias baked into them — and that the downstream consequences fall hardest on women.

4. The treatment is boring

There is no blockbuster drug in iron deficiency. Oral iron is cheap and generic. IV iron is available but rarely offered outside hematology and obstetrics. Nobody is marketing this diagnosis. The incentive structures of healthcare quietly push it down the priority list.

What to do if your Hb is "normal" but you suspect IDNA

Step 1 — Get the full panel, not the cheap one

Request a full iron panel: ferritin, transferrin saturation, MCV, haemoglobin, and CRP (for context). If you only get haemoglobin, you are not being assessed for IDNA; you are being assessed for anemia.

Step 2 — Know your interpretation thresholds

For premenopausal women:

• Ferritin < 30 µg/L = iron deficiency (BMJ / WHO alignment)
• Ferritin 30–49 µg/L = functional deficiency if symptomatic
• Transferrin saturation < 20% = corroborating evidence
• Elevated CRP → ferritin is inflated, interpret cautiously

Step 3 — Ask specifically about IDNA

The phrase "iron deficiency without anemia" in the conversation changes the clinical frame. Many GPs who would dismiss "low ferritin" will engage seriously when the question is framed as IDNA, because IDNA is an established diagnostic entity with ICD codes and treatment indications.

Step 4 — Discuss repletion, not reassurance

If your ferritin is under 30 and you have classical symptoms, the question is not whether to treat but how. Options:

• Oral iron — first line, cheap, works over 3–6 months, tolerated by ~60% of patients
• Alternate-day oral iron — better absorbed than daily dosing, fewer GI side effects
• IV iron — appropriate for oral intolerance, malabsorption, heavy menstrual bleeding outpacing absorption, or severe functional impact. Modern formulations (ferric carboxymaltose, ferric derisomaltose) are safe and reimbursed in many health systems.

Step 5 — Retest, don't just treat

Recheck ferritin 6–12 weeks into repletion. The goal is not just to climb above the "normal" floor but to restore adequate stores — typically ferritin ≥ 70 µg/L for durable symptom resolution.

A final word on being dismissed

If you have read this far, there is a reasonable chance you are in the middle of this diagnosis and nobody has helped you yet. I want to say three things directly:

1. You are not making it up. IDNA is a documented clinical entity with a substantial literature.
2. You are not alone in the experience of being dismissed. The exhausted-dismissed-then-diagnosed arc is the modal experience of iron deficiency in women under 45. It is a system failure, not a personal failing.
3. The fix exists and it works. In most cases, six to twelve weeks of appropriate repletion produces a recovery of energy, cognition, and exercise capacity that patients describe as "I didn't know I was this tired until I wasn't."

Do not let anyone tell you that a ferritin of 22 with four symptoms is nothing. It is not nothing. It is the early, treatable, named stage of an extremely common condition. You just have to insist on being met on the evidence.

This article is educational and not medical advice. Discuss significant changes to supplementation or testing with a qualified clinician.