Iron metabolism

Iron Metabolism


§   Largest component of body iron stores is blood (2500 mg)

§   Remainder found in the reticuloendothelial system in the

§        Liver (250mg)

§        Bone marrow (150mg)

§        Macrophages inc in spleen (500mg)

§   Tisues also contain iron enzymes (150mg) and myoglobin (300mg) 

§   Use about 20mg/ day, but majority comes from recycling of senescent red cells.

§   1-2mg/ day comes form our diet


§   Neonates have 80mg/kg iron which is used for growth

§   From 6 months to 2 years virtually no iron stores are present

§   Thereafter iron stores gradually accumulate to around 5mg/kg during childhood

§   Rises further in men to around 10mg/kg (women remains lower until the menopause)

Ferritin primary iron storage protein

§   Large molecule (480,000 mol wt) with a spherical shell enclosing up to 4000 iron molecules

§   Different subtypes (L in liver and spleen and H in heart and red cells)

§   Low levels of circulating ferritin contain very little iron and are predominantly L subtype)

§   Ferritin thought to be secreted by macrophages in response to changing iron levels



§   Water insoluble crystalline complex visible using Pearl’s stain

§   Higher iron to protein ratio and is probably formed by partial digestion of ferritin aggregates by lysosomal enzymes.

§   Largely found in macrophages rather than hepatocytes unless iron overload in which case found in both



§   Present in plasma and extravascular fluid (half life of 8-11 days)

§   Contains around 4mg iron at any one time but 30mg passes through each day

§   Transferrin receptors on the cell surface allow the uptake of transferrin (stain with CD71)



§   Similar structure to transferrin

§   Found in milk and neutrophils, also secreted onto surfaces as has bacteriostatic actions (preventing them growing by depriving them of iron)


Intracellular regulation of iron

§   Low iron levels lead to activation of the proteins IRP1 and IRP2 which bind Iron Response Element (IRE) sequences of mRNA.

§   Transferrin receptor mRNA has multiple IREs and binding by IRPs leads to increased stability and transcription by preventing degradation of the mRNA

§   Ferritin mRNA transcription inhibited by IRP binding


Iron absorption

§   Iron released from protein complexes by stomach acid – majority absorbed in duodenum

§   Reduced from Fe3+ to 2+ by Dcytb on the brush border and then transported across the membrane by DMT1.

§   Haem iron transported directly across the brush border and Fe released by haem oxygenase

§   Transported across the basolateral membrane by Ferroportin 1 and converted to Fe3+ by Hephestin

§   Ferroportin 1 activity inhibited by Hepcidin ie. hepcidin down regulates iron absorption and iron mobilisation

§   Hepcidin synthesised in the liver in response to:

§   increased iron stores ( HFE/ haeomjuvelin thought to be necessary for hepcidin synthsis.)

§   IL-6

§   Downregulated by anaemia/ hypoxia

§   Ie. hepcidin results in iron trapping within iron storage cells (macrophages) and a block in iron absorption from the gut.

§   Hepcidin deficiency (AR nonsense mutations in the HAMP gene) leads to severe juvenile haemochromatosis



Diagnositic methods for investigating iron metabolism


Serum ferritin

§        Correlates well with iron stores as assessed by quantitative phlebotomy or tissue biopsy in healthy individuals

§        Level <15 highly specific for iron deficiency

§        Spuriously increased in

§        Acute phase reaction

§        Tissue release of ferritin from iron rich organs (hepatic necrosis, chronic liver disease, splenic or bone marrow infarction eg in sickle cell)

§        Reduced in ascorbate deficiency

§        Rare hereditary disorder of ferritin synthesis (hereditary hyperferritinaemia) which is associated with normal iron levels – results in cataracts due to deposition of ferritin in the lens.


Red cell ferritin

§   Difficult to measure as extremely low levels in red cells and so not used in general practice

§   Has theoretical advantage that wouldn’t be affected by ferritin release into serum by tissue damage


Serum iron, total iron binding capacity (TIBC) and transferrin saturation

§        Labile – fluctuations mean that a single value may not reflect iron supply over a longer period

§        Iron levels have a diurnal pattern (lower in the morning than the evening)

§        Transferrin saturation = serum iron / TIBC

§        Reduces in iron deficiency due to combination of reduced iron and increased TIBC

§        Normal in anaemia of chronic disease

§        Increased hepcidin (mediated by Il-6) blocks iron release from macrophages and jejunal enterocytes

§        Sustained increase is an early change in the development of iron loading


Serum transferrin receptor concentration

§   Increased in iron deficiency

§   Concentration reflects both the number of erythroid precursors and iron supply to the bone marrow

§   Increased erythropoiesis will result in increased concentration

§   Sensitivity and specificity can be increased by using ferritin-transferrin receptor ratios

§   Assay is method specific and some consider that it adds little to information provided by ferritin assay


Red cell protophophyrin

§   Protoporphyrin accumulates in red cells when iron supply is restricted. 

§   Can measure red cell level (particularly zinc protoporphyrin)

§   Values may not reflect current iron supply

§   Levels also increased in sideroblastic anaemia and lead poisoning


Percentage of hypochomic red cells

§   Some analysers can measure this

§   Helpful in CRF in identifying iron deficiency early in patients on EPO (other measures likely to be confounded by chronic inflammation)

§   Helpful in diagnosing functional iron deficiency


Anaemia of chronic disease/ inflammation

§   Inadequate production of epo

§   Inadequate response of erythroid progenitors to epo

§   Impaired release of iron from stores secondary to increased hepcidin

§   Results in low iron and transferrin saturation, but with a high ferritin due to both stored iron which can’t be mobilised and acute phase response

§   Shortening of red cell survival

§   Treatment

§   Controversial

§   Can use erythropoietin – concerns regarding poorer overall survival/ progression free survival in cancer patients, therefore its use is restricted

§   Parenteral iron may be an alternative


Iron deficiency anaemia

1. Body stores depleted

2. Iron deficient erythropoiesis

§   Low serum transferrin saturation and ferritin

§   MCV / Hb may be normal

3. Iron deficiency anaemia

§   Microcytosis, poikilocytosis, target cells, reduced reticulocytes

§   Erythroblasts have ragged, vacuolated cytoplasm and pyknotic nuclei

§   Bone marrow macrophages show a total absence of iron

4. Tissue effects of iron deficiency

§        Severe and chronic iron deficiency causes widespread tissue changes

§        Koilonychia

§        Angular stomatitis

§        Glossitis

§        Pharyngeal webs (Patterson-Kelly syndrome)

§        Atrophic gastritis (reducing stomach acid and worsening iron absorption)

§        Very severe deficiency results in mitochondrial swelling which can cause impaired neutrophil function, mental development


Causes of iron deficiency

§        Diet

§        Vegetarians


§        Malabsorption

§        Coeliac disease

§        Achlorhydria

§        May show a response to oral iron


§        Increased requirements

§        Infancy – worse in premature babies and those with infections and delayed mixed feeding

§        Pregnancy (despite amenorrhea)


§        Blood loss

§        More than 6-8 mL/day (3-4 mg iron) becomes important

§        Menorrhagia

§        GI blood loss

§        Intravascular haemolysis leads to urinary iron loss



1. Oral iron

Ferrous sulphate (200mg provides 67mg iron)

Ferrous gluconate (300mg provides 36mg)


Need to provide 100-200mg iron / day in adults (3mg/kg in children)

Minimum response Hb rise of 2 g every 3 weeks


Failure to respond

§   Poor compliance

§   Ongoing haemorrhage

§   Malabsorption

§   Wrong diagnosis (anaemia of chronic disease, thalassaemia trait)


2. Parenteral iron

§   Usually unnecessary

§   Can be used in those genuinely intolerant of oral iron

§   Occasionally in malabsorption

§   Sometimes used when oral replacement can’t keep up with ongoing haemorrhage (eg HHT)

§   Chronic renal failure on epo (increased demand may outstrip ability to mobilise stores – functional iron deficiency)

§        Can increase mobilisation with ascorbic acid


§   Iron taken up by macrophages of the reticuloendothelial system which then release iron to circulating transferrin

§   Deficit in iron stores calculated from degree of anaemia (usually 1-2g)

§   Should be avoided if there is a history of allergy as anaphylaxis sometimes occurs

§   Other reactions include immediate nausea, urticaria and aches and pains as well as delayed reactions including fever, arthralgia and lymphadenopathy.  May also exacerbate rheumatoid arthritis. 

§   Venofer (iron sucrose) considered to be the safest form but can be excreted in urine exacerbating UTIs

§   Cosmofer (iron dextran) – IM or as a single dose iv


Iron overload


Causes of iron overload

Severe (>5g)

§        Increased absorption

§        Hereditary haemochromatosis

§        Massive ineffective haemopoiesis (beta thal intermedia, sideroblastic anaemia, CDA)

§        Increased iron intake (sub-saharan dietary iron overload / excess iron therapy)

§        Repeated red cell transfusions (congenital / acquired anaemia)

Moderate overload (<5g)

§        Chronic liver disease (alcoholic cirrhosis)

§        Porphyria cutana tarda

§        Rare genetic abnormalities of iron metabolism

§        Atranferrinaemia

§        Aceruloplasminaemia

Focal iron overload

§   Pulmonary haemorrhage / idiopathic pulmonary haemosiderosis

§   Chronic haemoglobinuria


Chronic iron overload syndromes of genetic origin

Mean age at diagnosis = 46yrs



§   Continued absorption of iron from the small intestine, despite normal/ increased total body iron

§   Due to hepcidin deficiency (type IV due to hepcidin resistance)

§   Low iron – reduced hepcidin – increased absorption

§   Hepcidin is an acute phase protein and this results in reduced absorption and anaemia of chronic disease




Classification of genetic haemochromatosis




Clinical features

Type 1



HFE gene

90% C282Y homozygotes

4% C282Y/H63D


Digenic disease described eg. HFE/HAMP mutations

Mutations result in reduced hepcidin secretion from the liver

Presents age 40-60

Cirrhosis (25% of whom get HCC), arthritis, diabetes, hypogonadism


Variable penetrance (lower incidence in women due to menstruation)

Type 2



Hemojuvelin gene – 2a

Hepcidin (HAMP) gene – 2b

Reduced hepcidin secretion

Juvenile onset

Severe phenotype


Type 3



Transferrin receptor 2 (TFR2) gene


Reduced hepcidin secretion

Mimics HFE

Type 4



Ferroportin gene

(hepcidin target)


Due to deficiency or malfunction of the main target of hepcidin

Ie. resistance

Subtype A

Low transferrin saturation (TS)

Macrophage iron deposition

Subtype B

Mimics HFE haemochromatosis

Type 5


DMT-1 mutation






HFE genetics


§   12% prevalence

§   1 in 200 homozygotes

§   90% of haemochromatosis due to homozygotes

§   Heterozygotes (for both C282Y and H63D) have slightly increased iron and transferrin saturation which may confer protection against iron deficiency



§   20% prevalence in UK population

§   C282Y/H63D heterozygotes account for 4% of haemochromatosis

§   Homozygotes may have higher ferritin and transferrin saturation than heterozygotes but significant iron accumulation is rare



§   Rare mutation that may cause mild iron accumulation in combination with C282Y or H63D




1. Candidates for testing

§   European ancestry with weakness, abnormal LFTs, arthralgia, impotence, DM, cirrhosis, pigmentation


2. Initial investigations

Transferrin saturation

§   Most sensitive and specific biochemical parameter

§   Fasting sample (if raised should be repeated on a fasting sample)

§   100 x serum iron/ TIBC (>55% in men, >50% in pre-menopausal women)

§   Not specific for HFE haemochromatosis – need to check CRP to exclude inflammation


§        Normal in the early stages of iron accumulation

§        If transferrin saturation is raised but ferritin normal should go on to do genetic testing

§        Close correlation (>300 in men, >200 in women)

§        >1000, severe clinical complications more likely

§   Falsely elevated in alcohol, dysmetabolic syndrome and inflammation


3. Confirmation of the diagnosis

HFE testing

§   Homozygous C282Y confirms diagnosis

§   Penetrance is variable, therefore not suitable for population screening

§   Heterozygotes C282Y/ H63D – mild variant

§   5% of patients with genetic haemachomatosis don’t have the identified phenotypes


4. If evidence of iron overload but HFE testing negative

Exclude other diagnosis (alcoholic liver disease / haematological disease)

Liver biopsy

§   Not necessary unless evidence of iron accumulation and genotype negative

§   Hepatic iron index > 1.9 (iron concentration in hepatic biopsy / age) diagnositic of haemochromatosis

Quantitative phlebotomy

§   Removal of 4g iron (20 phlebotomies of 450ml demonstrates that body iron stores are compatible with genetic haemochromatosis).


4. Staging investigations


§   AST

§   USS  cirrhosis, hepatoma. ?role of fibroscan – can grade cirrhosis

§   Liver biopsy - Determines whether there is cirrhosis

§   MRI – iron concentration but no information on cirrhosis


§   ECG and ECHO

Dexa scan

Endocrine tests

§   Glu, TFTs, bone profile, LH, FSH, testosterone etc.


Differential Diagnosis


§   Juvenile HC

§        Massive iron overload with endocrine and cardiac complications

§        Genetic testing for hemojuvelin and hepcidin mutations

§   TFR2 HC


§        TFR2 HC

§        Ferroportin disease – type B

§        AD, therefore diagnosis facilitated by documenting hyperferritinaemia in 1st degree relatives


Elevated ferritin with low transferrin saturation

§        Dysmetabolic syndrome

§        Multiple metabolic abnormalities

§        High ferritin / Normal TS

§        Mild hepatic iron excess

§        Mixed iron deposition in hepatocytes and macrophage

§        Ferroportin disease – type A

§        Macrophage iron excess

§        Hereditary aceruloplasminaemia

§        Chromosome 3

§        High ferritin / Low TS

§        Neurological syndrome

§        Undetectable levels of serum ceruloplasmin


Staging for C282Y homozygosity


Stage 0

Normal TS and ferritin



Yearly TS and ferritin

Stage 1

Increased TS but normal ferritin

Stage 2

Increased TS and ferritin




Stage 3


Stage 4

Organ damage predisposing to early death (DM, cirrhosis, cardiomyopathy)




Avoid ingesting large quantities of vitamin C containing food


Venesection - Start when ferritin raised but asymptomatic (stage 2)

1. Induction

§        Weekly – 450-500mls –

§        Calculate iron removed weigh bag – 450ml blood with Hb 13.5 contains 200mg iron

§        Absorption 3mg/day = 20mg/week

§        25 weekly venesections will remove 4.5g iron

§        Aim ferritin <20 and TS <16%

§        Withold if Hb <11


2. Maintenance

§        1-4 monthly

§        Aim ferritin <50 and TS <50


§   Serum ferritin should be checked at least every 2 venesections, and Hb checked within the week prior to venesection.


Liver cirrhosis

§   AFP and USS 6 monthly (monitoring for HCC)


Family screening


Ideas for the future

§        Oral iron chelators

§        Poor venous access

§        Anaemia

§        Poor tolerance of phlebotomy

§        Patient choice

§        Study ongoing with deferasirox

§        Inhibition of cellular iron transport

§        Correction of the systemic iron regulating defect


Iron chelators


Conditions associated with transfusional iron overload

§        Thalassaemia major

§        Blackfan-diamond anaemia

§        HbSS

§        Fanconi’s anaemia

§        Aplastic anaemia

§        Severe haemolytic anaemia

§        Repeated myeloablative chemotherapy

§        MDS


§        No physiological mechanisms to excrete excess iron


Goals of chelation therapy

§        Maintain iron balance with safe tissue iron levels

§        Prevention

§        Match transfused iron with chelated iron

§        Prevent iron reaching levels where tissue damage occurs

§        Rescue

§        Remove excess iron – slow process – finite pools

§        Reverse dysfunction

§        Detoxification of labile iron – 24 hour protection

§        Wide therapeutic safety margin of regime











Route of administratiom


Po - tds

Po  od


20 minutes

2-3 hours

8-16 hours


Urine/ stool



Dose range (mg/kg/day)_














Weekly then 6 monthly






Check 2x before starting










3 monthly

3 monthly


Liver iron




Cardiac iron

Annually after 10yrs

Annually after 10 yrs

Annually after 10 yrs

Pros and cons





Long safety record


Reversal of cardiac disease with intensive therapy

Can be combined with deferiprone


Enhanced removal of cardiac iron

Canbe combined with desferrioxamine


Once daily

Demonstrated equivalency to deferrioxamine at higher doses


Parenteral infusion

Ear, eye, bone toxicity

Poor compliance

Risk of agranulocytosis

Limited long term data

Moniter renal function

May not achieve negative iron balance in all at the highest doses



Combination deferioxamine and defriprone more rapidly reduce hepatic and cardiac iron than deferioxamine alone without increased toxicity


§        Patients beginning chelation with normal cardiac function

§        Defrasirox with regular assessment of iron burden to achieve correct dose


§        Patients with severe iron overload/ organ toxicity despite treatment with deferioxamine

§        Consider combining with deferiprone










Long-term experience

Effective in maintaining normal iron levels

Reversal of cardiac disease with intensive therapy

Can be combined with deferiprone

Parenteral infusion

Ear, eye, bone toxicity (skeletal dysplasia)

Poor compliance


Orally active

Safety profile well established

Enhanced removal of cardiac iron

May be combined with derioxamine

May not achieve negative iron balance (esp. in pts with less severe iron overload)

Risk of agranulocytosis

(0.5-1%, usually in the 1st year, rapidly reversible but usually occurs on rechallenge, may require GCSF)

SE – GI disturbance, arthralgia, increased ALT


Orally active

Once daily

Demonstrated equivalency to deferioxamine

Limited long term data

Increased creatinine (non-progressive)

May not achieve negative iron balance

SE – GI disturbance, rash, increased ALT