Summary
Transferrin is the primary protein that transports iron through the bloodstream from sites of absorption and storage to the bone marrow where red blood cells are made. Its level rises when iron stores are low (the body produces more carrier protein to capture available iron) and falls in iron overload — making it a valuable complementary marker in the investigation of iron status and anaemia.
Transferrin is assessed alongside serum iron to calculate transferrin saturation — the percentage of transferrin binding sites occupied by iron. Low transferrin saturation ( 45%) raises concern for iron overload.nnTransferrin also falls in malnutrition and liver disease, as the liver is the sole site of transferrin synthesis, making it a useful secondary marker of nutritional and hepatic status.
What It Is
Transferrin is a glycoprotein synthesised exclusively in the liver. Each molecule of transferrin has two iron-binding sites and can carry iron from intestinal absorption, recycled red cell iron, and storage sites to the bone marrow. The kidney, immune cells, and other tissues also take up transferrin-bound iron via specific receptors.nnTransferrin levels respond inversely to iron stores: iron deficiency stimulates the liver to produce more transferrin, increasing circulating levels and the overall iron-binding capacity (Total Iron Binding Capacity, TIBC). Iron overload suppresses transferrin synthesis.nnTransferrin saturation — calculated as (serum iron ÷ TIBC) × 100 — is one of the most useful derived markers for identifying both iron deficiency and iron overload.
Functions
Iron transport in the bloodstream
Binds iron from intestinal absorption and iron recycling, and delivers it to bone marrow for haemoglobin synthesis and to other tissues.
Iron buffering and protection
Keeps iron in a safe, soluble form in the blood, preventing free-iron-catalysed oxidative damage to tissues.
Iron deficiency indicator
Rises in iron deficiency as the liver produces more carrier protein to maximise iron capture — elevated transferrin is a key marker of deficiency.
Transferrin saturation calculation
Together with serum iron, transferrin allows calculation of transferrin saturation — a sensitive combined indicator of both deficiency and overload.
Reference Ranges
Serum Transferrin
Measured in g/L| Status | Range (g/L) | What it means |
|---|---|---|
| Low | < 2.0 | Low transferrin — consider liver disease, malnutrition, or iron overload. |
| Normal | 2.0–3.6 | Adequate transferrin production — iron transport function is normal. |
| Elevated | > 3.6 | High transferrin — consistent with iron deficiency; the liver is producing extra carrier protein to maximise iron acquisition. |
Transferrin must be interpreted alongside serum iron and ferritin. Transferrin saturation (serum iron ÷ TIBC × 100) of < 20% confirms iron deficiency; > 45% raises concern for iron overload. Transferrin is a negative acute-phase reactant — infection and inflammation lower it, potentially masking elevated levels seen in deficiency.
Symptoms of Imbalance
Transferrin symptoms reflect the underlying iron status disorder rather than the transferrin level itself.
- Symptoms of iron overload if transferrin saturation is high: joint pain, fatigue, abdominal discomfort
- Symptoms of malnutrition or liver disease if transferrin is low without iron overload
- Oedema and muscle wasting in severe protein-energy malnutrition
- Symptoms of iron deficiency anaemia: fatigue, pallor, shortness of breath
- Hair thinning and brittle nails
- Palpitations and reduced exercise tolerance
- Brain fog and difficulty concentrating
- Cold hands and feet
Causes of Imbalance
- Liver disease (cirrhosis, hepatitis) — liver cannot produce adequate transferrin
- Iron overload (haemochromatosis) — body reduces carrier protein when iron is excessive
- Malnutrition and protein-energy deficiency
- Chronic illness and systemic inflammation (negative acute-phase reactant)
- Nephrotic syndrome (transferrin lost in urine)
- Iron deficiency (most common cause — liver up-regulates production)
- Pregnancy (physiological increase in transferrin)
- Oral contraceptive use (oestrogen stimulates hepatic transferrin synthesis)
FAQs
Transferrin saturation is the percentage of transferrin’s iron-binding sites that are currently occupied by iron. It is calculated as (serum iron ÷ TIBC) × 100. Saturation below 20% strongly suggests iron deficiency even when ferritin is borderline. Saturation above 45% in men (or 40% in women) raises concern for iron overload and should trigger investigation for haemochromatosis.
When iron stores are depleted, the liver produces more transferrin as a compensatory mechanism — increasing the blood’s iron-carrying capacity to maximise capture of any available dietary iron. This is the same principle as TIBC rising in iron deficiency: more carrier protein means more potential binding sites.
Yes, if they also have liver disease, chronic inflammation, or malnutrition. These conditions reduce transferrin synthesis by the liver, potentially counteracting the iron-deficiency-driven rise. This is why interpreting transferrin alongside CRP and liver function tests is essential for accurate interpretation.
Ferritin reflects iron stores inside cells — it is the iron warehouse. Transferrin reflects circulating iron transport capacity. They move in opposite directions in iron deficiency: ferritin falls (stores depleted) while transferrin rises (more carrier protein made to collect iron). Together they provide a more complete picture than either test alone.
Yes. Oestrogen stimulates hepatic transferrin synthesis, causing transferrin to rise during pregnancy — a normal physiological change. Combined with the expanded blood volume of pregnancy, this contributes to the dilutional anaemia that many pregnant women experience and is why careful interpretation of iron markers in pregnancy requires reference to pregnancy-specific ranges.
References
- Camaschella C. Iron-deficiency anemia. N Engl J Med. 2015;372(19):1832–1843. View source
- Andrews NC. Disorders of iron metabolism. N Engl J Med. 1999;341(26):1986–1995. View source
- Ganz T. Systemic iron homeostasis. Physiol Rev. 2013;93(4):1721–1741. View source