Blood Chemistry-IronBlood Chemistry-Iron

Iron containing compounds

1. Iron compounds involved in cellular metabolism:- 

• A  – Haem. Iron compounds: 1-Haemoglobin : O2 carrying pigment in RBCs.

  2-Myoglobin :    O2 carrying pigment in muscles.

 3-Cytochroms: electron transport enzyme for oxidation metabolism.

Iron containing compounds

•  B – non-haem members:

          1- NADH Enzyme .       2- Succinic dehydrogenase enzyme.

2 – Those compounds required for iron storage:-

  Transferrin.  

  Hemosidrin.    

Ferritin. 

     Body iron storage

•  Total iron body contents ≈ 4 gm.  ¾ total iron body is found in O2 carriers; Hb  &  myoglobin ; and ¼ body iron is in stores.

 Approximate distribution of body iron is -:

• Circulating Hb 60%

• Bodystores              25%

• Myoglobin              10%

• B.M                        4%

• Enzymes 1%

• Plasma iron         <0.1%

RBC2500mg

Plasma Fe Transferrin Carries 4mg

20mg Fe Returned to Immature RBC in Bone Marrow

Daily RBC in B.M Production to Replace Old Cells 1%

R.E 20mg Fe Released Daily

Daily RBC Turnover of Old Cells 1%

���ABSORPTION1-2mg ONLY

���Loss Cells FromG.I Tract

1-2mg ONLY

Transferrin Carrier

Myoglobin

Respspiratory Enzyme

300mg

300mg

Transferrin Carrier

Body Stores

1000mg (male)

300-500mg (Female)

Daily Fe++ Turnover

Daily iron losses and requirements (WHO 2001)

Daily iron requirements

1. Iron is a one way element

3- daily iron requirement = amount lost + amount required 4- Increased requirement is found :

• A- menstruating female / 30-60 ml of blood in each cycle .This contains between 15-30 mg iron/cycle

B- pregnancy

(1) Foetal/placental growth requirement.     (2) Expansion in maternal mother blood volume.

     (3) Haemorrhage in delivery involve highly significant loss of iron.

2- absorption is increased in iron deficiency and decreased when body iron stores are deleted.

Iron Absorption

• The average western diet contain 10-15 mg of iron daily. Only 5-10% is absorbed.

• The main dietary sources are liver, red meat, green vegetables, spinach, supplemented cereals and fish.

Dietary iron falls into one of two categories • Inorganic iron, which mainly is present in cereals and

vegetables and Haem iron, which is found in haemoglobin and myoglobin of meat products.

Iron Absorption

• Inorganic compounds absorption is enhanced by the presence of reducing substances, which increase its solubility, such as ascorbic acid and other chelating agents such as Fructose, glucose, succinate which forms soluble complexes with iron. Conversely, inorganic iron absorption is retarted in the presence of substances, which decrease its solubility such as phosphates and phytates, which are present in cereals and also by alkaline pancreatic secretions. 

Control of iron absorption mucosal block theory

Iron Transport & Storage

•  Iron is transferred by specific carrier protein called Transferrin.

• Transferrin is b-globulin with molecular weight of 74,000, which can carry up to two ferric ions (Fe3+) per molecule.

• Iron is transported to bone marrow to developing erythroblast, which carry specific receptor to transferrin.

• The receptor-transferrin complex is internalized by the erythroblast, the iron is removed for utilization in haem synthesis and the receptor and apotransferrin return to the cell surface.   

Iron Transport & Storage

Iron Storage Forms

• ferritin : MW 45000, consist of  24 polypeptide sub-unit cluster together to form hollow sphere of 5 nm in diameter &  the stored iron form the central core of the sphere. Typically, ferritin contains about 25% of iron by weight. About 2/3 of body iron stores are present as ferritin.

• If the capacity for storage of iron in ferritin is exceeded, a complex of iron with phosphate and hydroxide forms. This is called hemosiderin; it is physiologically available.

Ferritin molecules store thousands of iron atoms within their mineral core. When excess dietary iron is absorbed, the body responds by producing more ferritin to facilitate iron storage

Ferritin Storage Molecule

Iron Storage Forms

• haemosiderin : it's not a single substance but a variety of different, amorphous, iron- protein

complexes. Typically it contains about 37% of iron by weight. Haemosiderin may represent

ferritin in various form of degradation. • As the body burden of iron increases beyond

normal levels, excess hemosiderin is deposited in the liver and heart. This can reach the point that the function of these organs is impaired, and death

Differential diagnosis of hypochromic anaemia.

Serum Transferrin receptor

• It reflects both the number of erythroid precursors & iron supply to the bone marrow.

• Serum Transferin receptor only increase in ACD in the absence of storage iron; so ferritin-transferin receptor ratio is used to diagnose ACD in general hospital practice.

Disorders of iron metabolism

• The state of iron deficiency is defined as a reduction below normal limits of the total body iron content.

• Iron deficiency anaemia is the most sever manifestation of iron deficiency, develops slowly through a series of successive stages, although progression from one stage to the next is not inevitable.

Stages of iron deficiency anaemia

1- Negative iron balance:

when the rate of absorption of iron from the diet is insufficient to meet the daily requirement, iron is mobilized from the body stores to meet the shortfall.

2- Latent iron deficiency:

A stage progress when the negative iron balance persists and the body iron

stores become depleted. In this stage the body is deficient in iron but

erythropoiesis is still normal and no adverse physiological effects are

present. Many people exist for prolonged period and never develop anaemia.

3 -Iron deficient erythropoiesis: this progresses when the iron body stores

are exhausted as a result of persistence of negative iron balance.

4 -Iron deficiency anaemia: this is the final stage of this sequence of

events, which develop after the BM is affected .

Causes of iron deficiency anaemia

1- Decreased supply of iron.

2- Increased requirement for iron

1- Decreased supply of iron

• 1st : Inadequate diet: This is considered as a seldom factor since the normal adult mixed diet contain 18 mg of iron/day, although it’s considered as a contributing factor to the more rapid onset of iron deficiency due to another primary cause.

• 2nd : Malabsorption of dietary iron: This relatively a common complication of diseases of the upper alimentary tract such as coelic disease. Partial gastrectomy or chronic anti-acid ingestion are major causes for the absence of stomach acid and subsequently impairs the absorption of dietary iron.

2 -Increased requirement for iron

There are three main causes of an increased in daily iron requirement:

A. loss of blood

B. growth & pregnancy

C. loss of iron

1st : blood loss

The most common causes of blood loss are: • Menestruation.• parasitic infection (Ancylostoma & necator

americanus).• Carcinoma, • duodenal ulcer. • hiatus hernia.• haemoroids and menorrhgia.

2nd : growth & pregnancy

Adolescence & pregnancy are known as periods of accelerated growth. This makes iron deficiency very common. For example:

• In normal, uncomplicated pregnancy, maternal total red cell volume increases 20%-40%. This imposes an extra requirement for iron of up to 500mg.

• The developing feotus, requires about 300mg. • Blood loss at delivery is compounded the iron balance. • The excess requirement for iron in pregnancy is offset

partially by amenorrhea which saves about 200mg of iron.

3rd : loss of iron

• chronic intravascular haemolysis can result in the loss of considerable amounts of iron as haemosidein in the urine.

Pathophysiology

Sever iron deficiency anaemia is accompanied by a wide range of clinical manifestation, this can be considered under two main headings:

• Effects on the blood & blood-forming tissue• Effects on other tissue

1st : effects on blood & blood-forming tissue

Decreased iron incorporation into the haemoglobin in the developing erythroblast leads to:

• Decreased Hb concentration denoted by decreased MCHC• Increased free protoporphyrin concentration within the cell• Mature microcytic red blood cell due to extra mitotic division before

the nucleus die.• Thus, the anaemia which accompain iron deficiency anaemia

typically is hypochromic and microcytic. • Reticulocytopenia is present.• The bone marrow represents erythroid hypoplasia, decreased

macrophage iron and normoblast have ragged cytoplasm. • One of the whole mark in the iron deficiency anaemia is the

combination of raised TIBC with reduced % saturation of transferrin and decreased iron concentration. Ferritin levels are also reduced.

Laboratory Studies in Iron Deficiency

2nd : General effects of iron deficiency

anaemia

• Koilonychia- Flattening or spoon of the nail.• Angular stomatitis- atrophic lessions at the

corner of the mouth.• Glossitis- smoothed, inflamed tongue.• Atrophic gastritis- inflammation of the lining of

the stomach• Achlorhydria- decrease in gastric secretion

• Pica: Soil-geophagia & Ice- pagophagia

Koilonychia

Anaemia of Chronic Disorder 

Anaemia of Chronic Disorder 

• Chronic inflammatory or malignant disorders frequently are accompanied by a normocytic, normochromic anaemia, which is refractory to all treatment except that which causes regression of the primary condition. This form of anaemia is known as anaemia of chronic disorders (ACD).

Pathophysiology• Chronic inflammation causes activation to macrophages and

upregulation of surface apotransferrin receptors. Binding of significant quantities of apotransferrin to macrophage reduces

TIBC. 

• Inflammation also stimulates neutrophils to synthesis and release large quantities of apolactoferrin, which acts as iron binding protein.

The apolactoferrin is bound to specific receptors on the activated macrophages and acts like a magnet for the circulating iron. Any

iron that is bound to the apolactoferrin:receptor complex is internalized by the macrophage and stored as ferritin. Thus

increasing tissue iron stores. 

• Erythropoietic activity of the BM is suppressed in ACD. This most likely to be caused by the release of growth inhibitors such as IL-1, γ-interferon and tumor necrosis factor in response to the primary condition. RBC life span is also reduced. 

Diagnosis of ACD

• Anemia (mainly normo-, event. microcytic)• Inflammatory disease, cancer• Low serum iron concentration• This could be true also for iron deficiency

anemia• FERRITIN – increased• TRANSFERRIN – decreases• IRON STORES – sufficient

H E P CIDIN)not available in clinical

practice(

Sideroblastic Anaemia

Sideroblastic Anaemia• The sideroblastic anaemias are heterogeneous group of

disorders, which are characterized by disordered incorporation of iron within the haem in developing erythroblasts.

• The resulting toxic accumulation of iron in the mitochondria of erythroblast leads to the formation of iron encircling the nuclei (ringed sideroblast) and ineffective erythropoiesis ensues. However, ringed sideroblasts are not specific indicators of sideroblastic anaemia: they are frequently found in leukaemia, megaloblastic anaemia and alcoholism.

 • The sideroblastic anaemias are classified according to their

aetiology as:• Hereditary • Secondary or idiopathic

Sideroblastic anaemia. Erythroblasts showingperinuclear rings of iron (Perls’ stain).

Siderocytes and sideroblasts.

• Siderocyte Mature red cell containing one or more siderotic granules (Pappenheimer bodies)

• Normal sideroblast Nucleated red cell containing one or more siderotic granules, granules few, difficult to see, randomly distributed in the cytoplasm, reduced proportion of sideroblasts in iron deficiency and anaemia of chronic disorders

• Abnormal sideroblasts Cytoplasmic iron deposits (ferritin aggregates): increased granulation, granules larger and more numerous than normal, easily visible and randomly distributed, proportion of sideroblasts usually parallels the percentage saturation of transferrin (e.g. haemolytic anaemia, megaloblastic anaemia, iron overload, thalassaemia disorders) Mitochondrial iron deposits (non-ferritin iron): ring sideroblasts in inherited and acquired sideroblastic anaemias

Hereditary Sideroblastic Anaemia

• They are X-linked inherited diseases, which are mostly characterized by functional deficiencies of enzymes of the haem synthetic pathway, most commonly δ-aminolaevulinic acid (δ-ALA) synthetase or ferrochelatase.

• Affected male have hypochromic, dimorphic anaemia with mild ineffective erythropoiesis and erythroid hyperplasia.  

Lead Poisoning

• Chronic lead poisoning was a relatively common condition when most drinking water was supplied via lead pipes.

• Lead is absorbed by inhalation or ingestion. • Most absorbed lead accumulates in bone & bone

marrow.• In bone marrow, lead is associated with red cell

precursors and more specifically with mitochondrial membranes and disrupts haem synthesis.

• This leads to sever sideroblastic changes.• Lead also cause damages to red cell membrane and

inhibits glycolytic activity. • These two activities result in mild haemolysis which

contributes to anaemia of chronic lead poisoning.

Investigation of lead poisoning

• Blood lead levels.

• The free erythrocyte protoporphyrin. (Lead particularly affects the enzymes involved in haem

synthesis; thus a screening test for early lead poisoning is the measurement of haem precursors).

• An abdominal radiograph may show radio-opaque lead

fragments in the gastrointestinal tract.

• Also lead lines may be seen on examination of a radiograph of bony structures because lead interferes with the growing ends of bones.

Secondary Sideroblastic Anaemia

1- Drug-induced Siderblastic A naemia:• The most common cause of this condition is

the administration of drugs such as Chloramphenicol and alcohol. These drugs inhibit the synthesis of δ A L A synthetase and ferrochelatase.

• The blood picture is the same as in hereditary sideroblastic anaemia.

Other investigations include

• urinary coproporphyrin

• microcytic hypochromic anaemia

• The blood film shows basophilic stippling in the red cells and reticulocytosis. The basophilic stippling result of the acculmulation of pyrimidine nucleotides in the cytoplasm and is only present in the youngest red cells.

3 -Idiopathic Sideroblastic Anaemia

• It's the disease of eldery and most common one. It's identical to the mylodyplastic syndrome refractory anaemia with sideroblast (RAS).

• Characteristic dyserythropoietic changes include macrocytosis, poikilocytosis, basophilic stippling and ringed sideroblast affecting all stages of erythroblast development.

• In the early stages of the disease platelets and leucocytes appear normal.

Iron overload

There three commonly encountered forms of chronic overload:

1- Hereditary haemochromatosis

2- Transfusion-associated haemochromatosis

3- Dietary causes

1 -Hereditary haemochromatosis

Hereditary haemochromatosis is:

• a multi-organ disease

• inherited in an autosomal recessive manner • the most common genetic disease in Northern Europe

• The disease results from the excessive absorption of iron which is subsequently deposited in tissues such as the pancreas, heart and liver.

• The normal body content of iron is 2-6 g; patients with haemochromatosis may have 50-60 g.

Pathophysiology • One of the major sign of this condition is greatly

increased % saturation with transferrin. • Thus, when iron is absorbed inappropriately and

released in circulation some may be unable to bind to transferrin because it's already fully saturated.

• About 30% of the circulating iron exists as ferric or ferrous and waiting for binding sites to be available.

• These ionic iron acts as a catalyst for formation of toxic oxygen radicals in the presence of NADPH.

• Oxygen radical compound are short-lived and extremely reactive causing extensive localized tissue damage.

• The most common one is hydroxyl radical (OH.).• Accumulated organ damage can result in hepatic

cirrhosis, skin pigmentation, diabetes and congestive heart failure.

Laboratory Findings

• raised serum ferritin • reduced total iron binding capacity - TIBC • raised iron binding saturation:

– >60% transferrin saturation in males – >50% transferrin saturation in females

• liver biopsy for parenchymal iron deposition • exclusion of secondary causes by examination of a

blood film, and if necessary, the bone marrow.

(The patient's siblings should be screened by measurement of iron, TIBC and genetic Screening tests.)

Radiograph of hand – patient with haemochromatosisshowing loss of joint space and erosion of cartilage at themetacarpophalangeal joints.

Liver biopsy for a patient with type 1 haemochromatosis, showing staining predominantly in parenchymal cells.

Liver biopsy for a patient with type 4 haemochromatosis, showing iron staining predominantly in Kupffer cells.

Symptoms

Treatment

• Early diagnosis and treatment with venesection permits the avoidance of all the complications of haemochromatosis.

• At first venesection should be performed weekly, and each time the patient attends a full blood count should be done, as well as checking the liver function. Iron, TIBC and ferritin should be checked monthly.

• Venesection stops when haemoglobin reaches 10 g per dl, and follow up is by checking bloods and venesection every three months.

• Chelation with desferrioxamine may be tried in rare patients who cannot tolerate venesection because of cardiac failure or anaemia.

Prognosis

• The arthropathy, hypogonadism and hepatic cirrhosis rarely resolve with treatment.

• Intensively treated patients show an 11% five year mortality rare compared to 67% in those not treated.

• Hepatocellular carcinoma, cardiac disease and liver failure are the main causes of death.

2 -Transfusion-associated Haemochromatosis

• Patients who are completely dependent on a program of regular blood transfusion as in thalassemia are exposed to extensive iron intake, which can't be excreted.

• Each transfusion of 400ml carries with it 200ml of iron.

• Steady accumulation of iron can lead to haemochromatosis. This can be removed by administration of chelating agent.

3- Dietary causes

• Iron overload due to dietary causes was reported to be a serious problem among people who are exclusively cooking in iron pots.

• Acute iron poisoning due to ingestion of large number of iron tablets for therapeutic use is one of the most common causes of fatal poisoning in young children.

• Chronic use of iron supplements in the absence of iron deficiency can lead to iron overload, because iron is absorbed by passive diffusion across the gut in this condition regardless of the state of the body iron stores.