Summary
Ferritin is the protein that stores iron inside cells throughout the body, particularly in the liver, spleen, and bone marrow. A small amount circulates in the blood, and this serum ferritin level accurately reflects the body's total iron reserves. It is the most sensitive blood test for iron deficiency — falling before serum iron, haemoglobin, or red cell size changes occur.
Ferritin deficiency is extremely common, particularly in women of reproductive age, athletes, vegetarians, and anyone experiencing heavy menstrual blood loss. Even slightly low ferritin — still technically within the ‘normal’ range — can cause fatigue, hair thinning, and reduced exercise capacity that significantly impacts quality of life.nnFerritin is also an acute-phase reactant — it rises during infection, inflammation, and liver disease, which can mask true iron deficiency. Measuring CRP alongside ferritin is essential when inflammatory conditions are suspected.
What It Is
Ferritin is a hollow, spherical protein complex that stores iron in a safe, soluble, non-toxic form. Each ferritin molecule can store up to 4,500 iron atoms. The majority of ferritin is found inside cells (intracellular), with a small fraction circulating in the blood (serum ferritin).nnSerum ferritin correlates closely with total body iron stores — each 1 µg/L of serum ferritin represents approximately 8 mg of stored iron. When iron stores are depleted, ferritin falls first, making it the earliest and most sensitive indicator of iron deficiency.nnConversely, ferritin rises as an acute-phase reactant during infection, inflammation, and liver disease — meaning it can appear deceptively normal or even elevated in the presence of true iron deficiency when inflammation is co-present. This is why CRP should always be checked alongside ferritin.
Functions
Iron storage protein
Safely stores iron within cells, preventing it from catalysing damaging free radical reactions while maintaining reserves for haemoglobin production.
Iron supply to bone marrow
Releases iron to transferrin for transport to the bone marrow, where it is incorporated into new red blood cells.
Acute-phase response participant
Ferritin is upregulated during infection and inflammation as part of the innate immune response, withholding iron from pathogens.
Neurological iron supply
Provides the iron needed for myelin synthesis, neurotransmitter production, and normal brain development and function.
Reference Ranges
Serum Ferritin
Measured in µg/L| Status | Range (µg/L) | What it means |
|---|---|---|
| Deficient | < 13 | Iron stores depleted — iron deficiency confirmed even before haemoglobin falls. Supplementation required. |
| Sub-optimal | 13–30 | Low iron stores — symptoms of deficiency common at this level. Dietary review and supplementation recommended. |
| Optimal | 30–150 | Adequate iron stores for normal physiological function and red blood cell production. |
| Elevated | > 150 | High iron stores — investigate for haemochromatosis, liver disease, or inflammatory/infective cause. |
Reference ranges differ by sex and age — men typically have higher ferritin than women. Values > 400 µg/L warrant clinical investigation for iron overload, liver disease, or inflammatory conditions. In women, ferritin > 200 µg/L should be investigated. Always interpret alongside CRP.
Symptoms of Imbalance
Low ferritin symptoms often precede anaemia — many people with significant ferritin deficiency have a normal haemoglobin.
- Persistent fatigue and low energy despite adequate sleep
- Hair shedding and diffuse hair thinning (telogen effluvium)
- Reduced exercise capacity and breathlessness on exertion
- Restless legs at night
- Brain fog, difficulty concentrating
- Cold hands and feet
- Brittle nails and nail ridging
- Palpitations at rest or with mild exertion
- Fatigue (also occurs in haemochromatosis despite high iron)
- Joint pain, particularly in the knuckles and hips
- Abdominal pain or discomfort
- Liver enlargement
- Sexual dysfunction and reduced libido (in haemochromatosis)
- Skin bronzing or darkening
- Cardiac arrhythmias in severe iron overload
Causes of Imbalance
- Heavy or prolonged menstrual periods (leading cause in women of reproductive age)
- Inadequate dietary iron — vegetarian, vegan, or restricted diets
- Pregnancy and breastfeeding
- Gastrointestinal blood loss (peptic ulcer, colorectal cancer, IBD)
- Intense exercise (sports-related iron loss)
- Coeliac disease or Crohn's disease impacting absorption
- Repeat blood donation
- Hereditary haemochromatosis (HFE gene mutations)
- Liver disease (alcoholic liver disease, hepatitis)
- Active infection or systemic inflammation (acute-phase response)
- Haemolytic anaemia
- Multiple blood transfusions
- Iron supplementation in excess
- Metabolic syndrome and insulin resistance
FAQs
Most laboratory reference ranges for ferritin start at 13–15 µg/L for women. However, many clinicians and researchers recommend a minimum of 30–50 µg/L for optimal health, hair, and energy. Symptoms of deficiency — particularly fatigue and hair loss — are common at levels below 30 µg/L, even when technically within the ‘normal’ reference range. Aim for a ferritin of at least 50–80 µg/L for symptom resolution.
Yes — and this is common. Iron deficiency progresses in stages: stores deplete (low ferritin) before serum iron or haemoglobin changes. Many people experience significant symptoms — fatigue, brain fog, hair thinning, restless legs — with low or borderline ferritin but a completely normal haemoglobin and blood count. Measuring ferritin directly identifies this ‘pre-anaemic’ iron deficiency.
Ferritin is an acute-phase reactant — the liver increases ferritin production during infection, inflammation, and liver disease as part of the immune response. Elevated ferritin in this context does not reflect iron overload but rather the inflammatory state. This is why CRP should always be measured alongside ferritin, and testing should ideally be deferred until after acute illness resolves.
Ferritin typically begins to rise within 4–6 weeks of consistent iron supplementation, but full replenishment of stores can take 3–6 months depending on the initial level and the underlying cause. Repeat testing at 3 months after starting treatment confirms whether stores have been adequately restored.
Yes. Athletes — particularly endurance runners and those in high-impact sports — experience accelerated iron loss through sweat, foot-strike haemolysis (red cell destruction from repetitive impact), gastrointestinal micro-bleeding, and increased turnover of red blood cells. Ferritin below 30–40 µg/L in athletes is associated with impaired performance, fatigue, and reduced VO₂ max.
References
- Camaschella C. Iron-deficiency anemia. N Engl J Med. 2015;372(19):1832–1843. View source
- Beard J, et al. Iron status and neural functioning. Annu Rev Nutr. 2003;23:41–58. View source
- Trost LB, et al. The diagnosis and treatment of iron deficiency and its potential relationship to hair loss. J Am Acad Dermatol. 2006;54(5):824–844. View source