Iron deficiency is the most common micronutrient deficiency worldwide. An estimated two billion people are affected — women of reproductive age, vegans, endurance athletes and growing children most of all. It often starts silently, with shrinking iron stores while hemoglobin still looks normal.
This guide shows how to quantify your iron deficiency risk — using the three key lab markers (ferritin, transferrin saturation and hemoglobin) plus a weighted symptom score.
The three stages of iron deficiency
Iron deficiency does not appear overnight. Clinically it unfolds in three stages — knowing them lets you act early:
- 1. Storage depletion (latent iron deficiency): Ferritin falls, hemoglobin and TSAT still normal. Early symptoms — fatigue, hair loss, restless legs — already appear.
- 2. Iron-deficient erythropoiesis: Transferrin saturation drops below 20 %. Red blood cells turn smaller and paler; hemoglobin is borderline normal.
- 3. Iron-deficiency anemia: Hemoglobin falls below the WHO cutoff (women 12.0 g/dL, men 13.0 g/dL). Classic anemia signs — breathlessness, tachycardia, pallor — come to the front.
Adult cutoffs
| Marker | Normal | Suggestive | Deficient | Severe |
|---|---|---|---|---|
| Ferritin (ng/mL) | ≥ 100 | 30–99 | 15–29 | < 15 |
| TSAT (%) | ≥ 20 | 16–19 | < 16 | — |
| Hb women (g/dL) | ≥ 12.0 | 11.0–11.9 | 8.0–10.9 | < 8.0 |
| Hb men (g/dL) | ≥ 13.0 | 11.0–12.9 | 8.0–10.9 | < 8.0 |
Important: Ferritin is an acute-phase reactant. In chronic inflammation, kidney disease or cancer ferritin is falsely elevated. There a value up to 100 ng/mL still counts as deficiency — and TSAT becomes the decisive marker.
Typical symptoms in the score
The calculator weights ten typical iron-deficiency signs — some nonspecific (fatigue), others highly specific (pica, restless legs):
| Symptom | Points | Note |
|---|---|---|
| Fatigue | 1 | Most common, but nonspecific |
| Pale skin | 1 | Inner eyelids, lips, nail beds |
| Shortness of breath | 2 | Reduced O₂-carrying capacity |
| Hair loss | 1 | Diffuse shedding, often with ferritin < 30 |
| Brittle nails | 1 | Ridges, spoon-shaped nails (koilonychia) |
| Restless legs | 2 | Highly specific for iron deficiency |
| Pica (ice, dirt) | 2 | Red flag — almost always iron deficiency |
| Cold hands/feet | 1 | Peripheral vasoconstriction |
| Headache | 1 | Cortical hypoxia |
| Poor concentration | 1 | Brain fog, slowed thinking |
Run the iron deficiency calculator
Ferritin, TSAT, hemoglobin and 10 clinical symptoms — instant result with severity and guidance. Anonymous and free.
Calculate for free →Common causes of iron deficiency
- Increased demand: Menstruation (especially heavy periods), pregnancy, growth, intensive endurance training.
- Reduced absorption: Vegan or vegetarian diet, gastric surgery, celiac disease, atrophic gastritis, frequent acid-blocker use.
- Blood loss: Peptic ulcer, hemorrhoids, colon cancer, frequent blood donations, NSAID-induced microbleeding.
- Chronic disease: Kidney failure, heart failure, inflammatory bowel disease — functional iron deficiency despite normal stores.
How iron deficiency is treated
- Oral therapy: 60–120 mg elemental iron per day, ideally fasting with vitamin C, away from coffee, tea or calcium. Newer trials show that dosing every other day is absorbed better than twice a day.
- Intravenous iron: For oral intolerance, severe deficiency, inflammatory bowel disease, or heart/kidney failure. Advantage: stores refill fast, often after one or two infusions.
- Cause workup is mandatory: In men and postmenopausal women a bleeding source (stomach, colon) must be ruled out — supplementing iron without diagnosing the cause can mask a malignancy.
Related calculators
Iron deficiency and anemia are closely linked, but not every iron deficiency leads straight to anemia. To check whether you are already anemic, run our Anemia Risk Calculator. Because fatigue and dyspnea on exertion can also stem from a weak thyroid, take a look at the Thyroid Function Calculator. If your energy budget feels low overall, the BMR calculator helps separate diet-related from disease-related fatigue.
Bottom line
Iron deficiency is common, treatable — and starts long before anemia. With our Iron Deficiency Calculator you see in seconds whether your numbers and symptoms are off. With ferritin under 30 ng/mL, TSAT under 20 % or several typical symptoms, book a GP visit — usually a simple blood test is enough for diagnosis.