Iron Deficiency Staging Interpreter
Iron Deficiency Staging Interpreter
Place a patient on the spectrum from depleted stores through iron-deficient erythropoiesis to frank iron deficiency anaemia.
Iron Deficiency Staging
Ferritin + TSAT + HbFerritin 18 µg/L, TSAT 14%, Hb 10.8 g/dL, female
The three stages
Stage 2 — iron-deficient erythropoiesis: ferritin ↓, TSAT ↓, Hb normal
Stage 3 — iron deficiency anaemia: ferritin ↓, TSAT ↓, Hb ↓
- ferritin < 30 µg/L
- depleted stores in the absence of inflammation
- TSAT < 20%
- restricted iron supply to the erythroid marrow
- Hb threshold
- 13 g/dL in men, 12 g/dL in non-pregnant women (WHO)
Worked example
Ferritin 18 µg/L, TSAT 14%, Hb 10.8 g/dL, female
Ferritin below 30 → stores depleted
TSAT below 20% → supply restricted
Hb 10.8 below the 12 g/dL threshold → iron deficiency anaemia
The sequence of change
| Stage | Ferritin | TSAT | Haemoglobin | MCV |
|---|---|---|---|---|
| 1 — depletion | Low | Normal | Normal | Normal |
| 2 — deficient erythropoiesis | Low | Low | Normal | Normal or falling |
| 3 — anaemia | Low | Low | Low | Low |
Why staging matters
Iron deficiency develops in an orderly sequence, and knowing where a patient sits on it changes what you do. Storage iron goes first, and ferritin falls while everything else stays normal. Only when stores are exhausted does supply to the marrow fail, and transferrin saturation drops. Haemoglobin falls last of all, and microcytosis appears later still, once a significant proportion of circulating cells have been produced under iron restriction.
The practical consequence is that waiting for anaemia means waiting for the final stage of a process that has been running for months. Symptomatic iron deficiency without anaemia is real and common — fatigue, reduced exercise tolerance, restless legs, hair loss and impaired cognition all occur at stage 1 and 2 — and responds to replacement.
It also means a normal haemoglobin and a normal MCV never exclude the diagnosis. In a patient with suggestive symptoms, ferritin and transferrin saturation are the tests that answer the question. And at every stage the same second question applies: iron deficiency in an adult is a symptom, not a diagnosis, and the source of loss needs identifying.
Frequently asked questions
Can you be iron deficient without anaemia?
Yes, and it is common. Stores are exhausted long before haemoglobin falls. Fatigue, reduced exercise tolerance, restless legs and hair loss all occur at this stage and respond to iron replacement.
What ferritin confirms iron deficiency?
Below 30 µg/L in an adult with a normal CRP. If inflammation is present the threshold rises to about 100 µg/L, because ferritin is an acute-phase reactant.
Does a normal MCV rule out iron deficiency?
No. Microcytosis is a late finding and requires a substantial proportion of circulating red cells to have been made under iron restriction. Many iron-deficient patients have a normal MCV.
What investigation follows a diagnosis of iron deficiency?
In an adult, the source of loss. Unless menstrual loss fully accounts for it, gastrointestinal investigation is indicated, along with coeliac serology.
Related calculators
References
- Camaschella C. Iron deficiency. Blood. 2019;133(1):30–39.
- WHO. Haemoglobin concentrations for the diagnosis of anaemia.
- Snook J et al. BSG guidelines for the management of iron deficiency anaemia in adults. Gut. 2021;70(11):2030–51.