Low ferritin with normal haemoglobin indicates iron deficiency without anaemia (IDWA), also termed non-anaemic iron deficiency (NAID). This represents depleted iron stores before haemoglobin has been affected, essentially the earliest stage of iron deficiency.
<keypoints> - IDWA is **at least twice as common** as iron deficiency anaemia globally - Ferritin <30 µg/L confirms iron deficiency (sensitivity ~92%, specificity ~98%); in chronic inflammation, use a threshold of <100 µg/L and check TSAT - Patients can be **symptomatic** despite normal Hb: fatigue, reduced cognition, impaired exercise tolerance, restless legs, hair loss - Treatment is indicated when identified; oral iron is first-line, target ferritin >100 µg/L - Cause should be investigated: menstrual loss, dietary insufficiency, malabsorption (coeliac disease), or GI blood loss (especially in men and postmenopausal women) </keypoints>Stages of Iron Depletion
Iron deficiency exists on a continuum:
- Iron depletion (low ferritin, normal serum iron, normal Hb): stores are running low
- Iron-deficient erythropoiesis (falling transferrin saturation, rising TIBC): supply to marrow is compromised
- Iron deficiency anaemia (Hb falls, MCV drops): full-blown IDA
Low ferritin with normal Hb sits in Stage 1 or early Stage 2. Without intervention, progression to IDA is expected.
Key Diagnostic Points
- Ferritin is the diagnostic test of choice. In Australia, iron deficiency is diagnosed when ferritin <30 µg/L in adults.
- Ferritin is an acute-phase reactant: may be falsely normal/elevated in infection, inflammation, liver disease, or malignancy. Check CRP if clinical suspicion is high.
- If ferritin is indeterminate (30-99 µg/L) and symptoms are present, check ; <20% supports iron deficiency.