What do iron studies showing low ferritin with normal haemoglobin typically indicate?

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.

Stages of Iron Depletion

Iron deficiency exists on a continuum:

1. Iron depletion (low ferritin, normal serum iron, normal Hb): stores are running low
2. Iron-deficient erythropoiesis (falling transferrin saturation, rising TIBC): supply to marrow is compromised
3. 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 transferrin saturation (TSAT); <20% supports iron deficiency.
• MCV is often still normal at this stage, so a normal MCV does not exclude iron deficiency.

Common Causes to Consider

GI investigation is particularly important in men and postmenopausal women, as approximately one-third with iron deficiency have underlying GI pathology, including malignancy.

Management

• Oral iron is first-line: elemental iron ~100 mg daily (e.g. ferrous sulfate 325 mg). Alternate-day dosing may improve absorption and reduce GI side effects.
• Target ferritin >100 µg/L, with symptom resolution as a clinical endpoint.
• Recheck FBC and ferritin at 8-10 weeks.
• IV iron (e.g. ferric carboxymaltose) is reserved for oral intolerance, malabsorption, or need for rapid repletion.
• Monitor ferritin every 6-12 months after repletion, especially in at-risk groups.