Post on 11-May-2015
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Classification of Anaemia: Microcytic Hypochromic Anaemia
Classification of AnaemiaMicrocytic &
Hypochromic Normochromic & Normocytic Macrocytic
MCV<RRMCH<RR
Defects in haem
synthesis
Defects in globin
synthesis
•Iron deficiency •ACD•Sideroblastic (congenital)
•Thalassaemia•Haemoglobinopathies
MCV within RRMCH within RR
Acute blood lossHaemolysisACDMarrow infiltration
MCV>RR
Megaloblastic Non-megaloblastic
B12/Folate deficiencyLiver diseaseDrug inducedMDS
Iron Regulation
Normal Iron Absorption and Metabolism
Ferritin• Iron storage protein• Produced by all living organisms including bacteria, algae, &
higher plants and animals• In humans, it acts as a buffer against iron deficiency and iron
overload• Consists of:
• Apoferritin – protein component• Core- ferric, hydroxyl ions and oxygen
• Largest amount of ferritin-bound iron is found in:– Liver hepatocytes (majority of the stores)– BM– Spleen
• Excess dietary iron induces increased ferritin production• Partially digested ferritin= HAEMOSIDERIN- insoluble and can be
detected in tissues (hepatocytes) using Perl’s Prussian blue stain
Transferrin (Tf)
• Transports iron from palsma to erythroblast• Mainly synthesized in the liver• Fe3+ (ferric) couples to Tf• Apotransferrin = Tf without iron• Contains sites for max 2 iron molecules• The amount of diferric Tf changes with iron status
– Levels decreased when cellular iron demand is increased– Increased levels lead to increase hepcidin production that
decreases iron absorption
Transferrin Receptor (TfR)
• Provides transferrin- bound iron access into cell• Control of TfR synthesis is one of major
mechanisms for regulation of iron metabolism• Cells maintain appropriate iron levels by altering TfR
expression and synthesis• Increased by iron deficiency
• Located on all cells except mature RBC• Can bind up to 2 Tf• apoTf is not recognized by TfR
Ferroportin
• Transmembrane protein• Found on the surface of most cells:
• Enterocytes • Hepatocytes • RE system
• Regulates iron release from those tissues (iron exporter)
• ‘Hepcidin receptor’
Hepcidin
• Is an antimicrobial peptide produced in the liver• Act as a negative regulator of intestinal iron absorption &
release from macrophages• Hepcidin binds to the ferroportin receptor & cause
degradation of ferroportin, resulting in trapping of iron in the intestinal cells
• As a result, iron absorption & mobilization of storage iron from the liver & macrophage are lowered
• Increased synthesis of hepcidin occurs when transferrin saturation is high and decreased synthesis when iron saturation is low
Causes of Iron deficiency
Major causes of IDA in Western
Society
Blood loss:•GIT•Urinary
Increased demand:• Growth
• Pregnancy
Inadequate intake• Infants
• vegetarian
Iron sequestration at inaccessible sites (pulmonary haemosiderosis)
Malabsorption
Haemolysis
Major causes of IDA in developing
countries
Parasitic infection
Malnutrition
Symptoms of Iron Deficiency
• Mainly attributed to anaemia– Fatigue– Pallor– Shortness of breath– Tachycardia– Failure to thrive
• More specific features (only apparent in severe IDA ):– Koilonychia– Glossitis– Unusual dietary cravings (pica)
Stages of Iron Deficiency
• 3 stages• Stage 1• Characterized by a progressive loss of storage iron• Body’s reserve iron is sufficient to maintain
transport and functional compartments through this phase, so RBC development is normal
• No evidence of iron deficiency in peripheral blood and patient experiences no symptoms
• Stage 2• Defined by exhaustion of the storage pool of
iron• For a time, RBC production is normal relying on
the iron available in transport compartment• Anaemia may not be present but Hb level starts
to drop• Serum iron, ferritin and Tf saturation decreased • Increased TIBC, Tf and TfR
• Stage 3• Microcytic hypochromic anaemia• Having thoroughly depleted storage iron and
diminished transport iron, developing RBCs are unable to develop normally
• The result is first smaller cells with adequate [Hb], although these cannot be filled with Hb leading to cells becoming microcytic & hypochromic
• FBE parameters & iron studies all outside RR
Diagnosis - FBE
• Hb or borderline• RBC• Hct/PCV • MCV• MCH• MCHC• RDW • +/- thrombocytosis• Elongated cells• Target cells (severe IDA)
Diagnosis- Iron studies
Ferritin Serum Iron
Transferrin Tf Saturation
TIBC TfR
Results in IDA
Differential diagnoses
• Thalassaemias/ Haemoglobinopathies– Not all hbpathies are microcytic and hypochromic
• Anaemia of chronic disease• Congenital sideroblastic anaemia
Treatment of Iron Deficiency
• Treatment of underlying cause (ulcers)• Dietary supplementation
– Oral supplements• Transfusion
– If anaemia is symptomatic and life threatening– No prompt response to treatment
• Dimorphic blood film is present in treated IDA– With oral supplements-newly produced cells are
normochromic normocytic– Transfused cells are normochromic and normocytic
Anaemia of Chronic Disease
• Anaemia of chronic inflammation• Usually normochromic normocytic; microcytosis &
hypochromia develop as the disease progress• Iron stores abundant, but iron is NOT available for
erythropoiesis• There are several proposed mechanism for abnormal iron
haemostasis in ACD:• Lactoferrin competes with transferrin for iron
– RBC don’t have lactoferrin receptors
• Ferritin increases• Cytokines inhibit erythropoieis• HEPCIDIN
ACD- Role of Hepcidin
• Increase in hepcidin:– Levels can be increased up to 100 times in ACD– Release from liver after stimulation by IL-6– Acute phase reactant
• Binds to ferroportin– Decreases iron absorption and export from cells
Diagnosis & Treatment
• Identification of the disease• CRP & IL 6• Measurement of hepcidin levels via ELISA, HPLC or LCMS• Iron studies to distinguish from IDA• Failure to respond to iron supplementationTx:• Maintaining normal Hb is challenging• EPO administration + IV iron• Anti-inflammatory therapy
Sideroblastic anaemia
• Can either be inherited or acquired• Rare condition• Most common mutation is in ALA synthase gene
(ALAS2) located on X chromosome• Abnormal haem synthesis & presence of ringed
sideroblasts in erythroid precursors (visible if stained with Perls Prussian Blue)
• Microcytic hypochromic anaemia– Ineffective erythropoiesis – Systemic iron overload
STRUCTURE OF HAEMOGLOBIN
Polypeptides are made up of 2a chains and 2B chains, a2B2. Haem groups bind oxygen.
STRUCTURE OF HAEM
• Haem structure: the iron (Fe)at the centre enables oxygen to bind
Development of Haemoglobin
Stages of Haemoglobin Development
• Embryonic haemoglobin– Hb Gower 1 z2e2
– Hb Portland a2g2
– Hb Gower 2 a2e2
• Foetal Haemoglobin– Hb F a2g2 Foetus 100% Adult <1%
• Adult haemoglobins – Hb A2 a2d2 Adult 1.8-3.6%– Hb A a2b2 Adult 96-98%– The globin genes are arranged on the chromosomes in order of
expression
Inherited defects of globin synthesis
• These are due to:1. Synthesis of an abnormal haemoglobin eg
haemoglobinopathies2. Reduced rate of synthesis of α or β chains:
thalassaemia
Β- Thalassaemia
• Caused by defective B globin chain synthesis• Due to mutations in the B globin gene• The unpaired α chain precipitate in the developing
cells leading to damage to the RBCs surface ~ leading to removal of RBCc by macrophages
• Leads to ineffective erythopoiesis• The more α chain in excess, the more haemolysis
occurs• Can be divided into B-thal minor and B-thal major
B-thal minor
• Results when 1 of the 2 gene that produces B- chain is defective (heterozygous)
• Usually present as a mild asymptomatic anaemia
• Hepatomegaly and splenomegaly are seen in some patients
B-thal major
• Characterized by severe anaemia first detected in early childhood as σ to β switch takes place
• Patient presents with jaundice, hepatosplenomegaly, marked bone changes (frontal bossing)
α thalassaemia
• Due to large deletions in the α globin genes• Notation for the normal α gene complex or
haplotype is expressed as α α, signifying 2 normal genes on chr 11
• There are 4 clinical syndromes of α thalassaemias; silent carrier, α-thal minor/trait, HbH disease (due to accumulation of unpaired B chain, homozygous α-thal (hydrops foetalis)
Signs & Symptoms of Thalassaemia
• Severe anaemia first detected in early chilhood
• Jaundice, hepatosplenomegaly, marked bone changes (frontal bossing)
• Microcytic hypochromic anaemia
Laboratory Findings
• Most thalassaemias are microcytic & hypochromic• Hb and PCV, MCV• RCC• Poikilocytosis, target cells, elliptocytes,
polychromasia, nRBCs, basophilic stippling• Bone marrow – hypercellylar with extreme erythroid
hyperplasia• Electrophoresis- decresead % of Hb A• Supravital stain to detect α thalassaemia major (HbH)
Treatment
1. Transfusion2. Iron chelation therapy- desferrioxamine3. BM transplantation4. Hydroxyurea- to increase Hb F levels enough to
eliminate transfusion requirements for patients with thalassaemia major
Hb 107 120-160g/LRCC 5.50 3.80-5.401012/LMCV 61 80-100 fLMCH 19.5 27-32 pgHb A2 5.0 1.8-3.5 %Hb F <0.1 0.0-1.0 %
Comparison of a normal blood film with b-thal major
Normal Blood Film Intermittently transfused b-thal
HbF>90%Bain B. ‘Blood Cells. A practical guide’2006 Free a chains form Heinz bodies and inclusions
Marked haemolysis reticulocytosisBasophilic stippling and Pappenheimer bodies
HbH Disease
Study Questions
• What are the main causes of IDA?• Draw a diagram that explains how iron
haemostasis is maintained in the body• Discuss different stages of development of IDA• How would you differentiate between different
microcytic and hypochromic anaemia?• Explain the involvement of iron regulatory
proteins in ACD
Study Questions• Describe how you would approach the investigation of a patient who has been
diagnosed with mild microcytic hypochromic anaemia. In your answer include the tests, expected results and how they would help you differentiate the disorders to make a final diagnosis.
• Are thalassaemias & haemoglobinpathies the same? Why?• Why do patients with iron deficiency and a suspected thalassaemia need to receive
iron replacement therapy before Hb electrophoresis and HPLC can be performed? How does iron deficiency influence these tests and the results obtained?
• Describing the principle and rationale, explain why Hb electrophoresis and HPLC can be used to diagnose these disorders. Are there any analytical errors that could lead to inaccurate results?
• What role does prenatal diagnosis & genetic counseling have in this group of disorders?