Red Cell Disorders 1 Flashcards
Examples of Red Cell Disorders
- Iron Deficiency
-Megaloblastic Anaemia
-Haemolytic Anaemia - Inheritred / Acquired
What is Anemia?
Reduced oxygen carrying capacity causing insufficient tissue oxygenation
Symptoms of Anemia
SOB (Shortness of breath), tachycardia, paleness ect
What is a full blood count? Why do it for Anaemia?
FBC: counting of all different cell types in the blood.
Anaemia results in lack of red cells and haemoglobin
Reference range: Male 135-180 g/L and Female 115-160 g/L
Anemia - important values for RBC
Mean corpuscular volume (MCV) is important (average size and volume of a red blood cell) - normal/ reference range: 80-102 fl.
- calculated by multiplying the percent hematocrit by ten divided by the erythrocyte count
RDW (Red cell Distribution Width) also important - normal range is 11-15 fl.
- calculated by dividing the standard deviation (SD) of the mean corpuscular volume (MCV) by the MCV and multiplying by 100 to yield a percentage value to be on behalf of the RBC size heterogeneity
hereditaryAnaemia - Causes
- Blood Loss, acute and chronic, can it be distinguished by a FBC ?
- Haematinics deficiency.
- Genetic disorders of: Haemoglobin/ Red cell metabolism/ Red cell membrane
Red cell destruction (haemolysis). - Disorders affecting the bone marrow e.g. leukaemia.
- Chronic diseases e.g. renal failure.
etc.
Anemia - Classification due to red cell size
Microcytic (low MCV) - e.g. IDA, ACD, thalassaemia
Macrocytic (high MCV) -e.g. megaloblastic anaemia
Normocytic (normal MCV) - e.g. haemolytic anaemias, blood
loss, ACD
MCV reference range: 80-102 fL
Iron Deficiency Anaemia (IDA): Iron Metabolism
Used in redo reactions in most cells
-potentially toxic
-Sequested in transport and storage molecules (ferritin, haemosiderin, transferin)
Haem iron most easily absorbed
Absorption of iron involves passive diffusion and receptors
Most iron found in red cells (Hb)
IDA; most common cause of anemia worldwide
Iron metabolism - Ferritin
-Main iron storage protein
-Soluble - measured in plasma
-Found in all cells - highest concentration in liver/spleen/bone marrow
- makes iron available for critical cellular processes while protecting lipids, DNA, and proteins from the potentially toxic effects of iron.
Iron Metabolism - Haemosiderin
-Insoluble, crystalline protein
- Found predominantly in macrophages
- Stained by Prussian Blue Reactions
- Iron-storage complex that is composed of partially digested ferritin and lysosomes.
-Breakdown of heme gives rise to biliverdin and iron - body then traps this iron and stores it as haemosiderin in tissues
Iron Metabolism - Transferrin
-blood plasma glycoprotein
- responsible for ferric-ion delivery: functions as the most critical ferric pool in the body and has a cruical role in iron metabolism.
- Delivers iron to cells with transferrin receptors; e.g erythroblasts in the bone marrow and cells all over the body.
Transferrin Receptors
-Cells require transferrin receptors for uptake of iron - e,g red cells.
Hepcidin
- Protein synthesized in the liver in response to iron levels and inflammation
-Transfer to plasma depends on the requirements of the eythron for iron and available iron stores. - Hepcidin controlls this
accquiredCauses of Red Cell Disorders (Anaemia)
-Dietary
-Blood Loss: Peptic ulcer, aspirin, menorrhagia, postmenopausal bleeding, hookworms, chronic and acute
-Malabsorption: Gastrectomy, IBD, Coeliac Disease
- Increased physiological demands: Infancy, pregnancy
Symptoms of Red Cell Disorders (Anemia)
- Lethargy/ Shortness of Breath
- Koilonychia
- Angular stomatitis
- Glossitis
-Irritability and poor cognitive function in children
Diagnosis - Assessment of iron status for anemia
Bone marrow (not routine for simple IDA)
Low ferritin
Low serum iron
Increased TIBC
Increased soluble transferrin receptors (sTfR) -not routine in most labs.
Blood tested against FBC parameters such as WBC, HB, MCV, MCHC, PLT.
Diagnosis - Microcytic hypochromic anaemia
Microcytic: circulating RBCs are smaller than the usual size of RBCs
hypochromic: RBCs have decreased red color
Diagnosis: Pencil vs Target cells
Pencil cells: elongated, hypochromic RBCs, in which the long axis was more than 3 times the length of the short axis
Target cells: RBCs with a central hemoglobin- ized area surrounded by an area of pallor.
-Pallor: an abnormally pale appearance.
Treatment
Oral Iron e.g. ferrous sulphate or ferrous gluconate.
Usually required for 3-6 months or more.
Treat underlying cause.
causes of Anaemia of Chronic Disease
- Associated with inflammatory disorders (E.G malignancy and RA) due to production of inflammatory cytokines (IL-6).
- Causes of anemia often multi-factorial:
- Defective iron incorporation into developing red cells
- A reduced erythropoietin response to anaemia
- Decreased sensitivity of erythroid precursors to erythropoietin.
- Shortened red cell survival.
- Hepcidin plays a important role
Anaemia of Chronic Disease - Lab Investigations
About 30-50% are microcytic
Hb usually above 90g/L
Normocytic/mild microcytic anaemia
Rouleaux
Raised ESR/CRP
Normal/increased ferritin
Reduced serum iron & TIBC
Little or no effect on sTfR
Vitamin B12 & Folate Deficiency (Megaloblastic Anaemia)- effect on erythropoiesis
Megaloblastosis: Due to faulty DNA synthesis
Nucleus of developing erythroblast maintains primitive appearance despite maturation and haemoglobinisation of the cytoplasm
Low B12 and folate levels result in failure to convert dUMP to dTMP
Conversion of deoxyuridine monophosphate (dUMP) to deoxythimidine monophosphate (dTMP) during DNA sythesis via methyl group transfer is facilitated by vitamin B12 and folate - leads to ineffective erythropoiesis.
Role of dTMP
dTMP is subsequently phosphorylated to produce dTTP, a vital precursor for DNA replication and repair.
What do you need b12 for
B12 is only present in food of animal origin
Can take 3 -5 exhaust stores
B12 required for normal blood production and nerve function
Causes of B12 deficiency
Poor nutrition
Malabsorption: Chrons disease, Tapeworms, Deficiency of Intrinsic Factor (essential for B12 absorption)
- Gastrectomy
- Perneicious anemia
- Autoimmune attack on gastric mucosa leading to stomach atropy
Diagnosis of B12 deficiency
antiperiatal antibodies, pernicious anemia
folate sources: Folate Deficiency
-Folate found in plant and animal food (especially liver)
- Easily destroyed by cooking
-Stores 3 months
Folate Deficiency - Causes
- Nutritional : (Especially old age, severely ill, special diets etc.)
- Malabsorption: Crohns disease, Tropical Sprue, Gluten induced enteropathy.
- Increased requirement: e.g Pregnancy, Renal Dialysis, Haematological Disorders (HA, myelofibrosis)
- Drugs : anticonvulsants, alcohol
- Liver Disease
Clinical features and symptoms of B12 and folate deficiency
- Weakness, tiredness, SOB, weight loss
- Diarrhoea, constipation
- Glossitis and angular cheilosis
- Jaundice
Low platelets occasionally lead to bleeding
Low WBC occasionally leads to infections
Neural tube defect (Spina Bifida)
Vitamin B12 deficiency can lead to
Progressive neuropathy
Degeneration of the spinal cord
Optic atrophy
Cerebral symptoms i.e. muscle weakness, paraesthesia, walking difficulty and psychotic disturbances.
anemia- Lab investigations
FBC.
Morphology
Bone marrow (if severe, unexplained macrocytic anaemia).
Serum B12 and Folate Levels (enzyme-linked immunosorbent assays).
Red cell folate levels.
IF antibodies.
Treatments of Folate / B12 deficiency
Determine underlying cause e.g. Reduced alcohol intake, Improved diet , Treat underlying disorder.
Folic acid supplements
B12 injections
Blood transfusion should be avoided if possible as it may cause circulatory overload. (TACO)
Haemoglobin - Structure
Consists of four globin chains each containing a haem group with iron.
Different types of haemoglobin and their chromosomes
Normal, adult blood contains 3 types of haemoglobin with different globin chains: alpha 2 beta 2- Hb A(97%), alpha 2 sigma 2 (2.5%)-HbA2, alpha 2 gamma 2- HBF (0.5%)
a-globin genes found in chromosome 16
b-globin genes found on chromosome 11
What is the major haemoglobin in foetus’?
Hb F
Qualitative or quantitiative defects in Hb synthesis
Qualitative defects involve abnormalities in the structure or function of the hemoglobin molecule itself
quantitative defects involve abnormalities in the overall production or concentration of hemoglobin.
trait conditions occuring when an individual inherits one abnormal and one normal gene
hemoglobin synthesis Quantitative defects
Caused by reduced / imbalanced synthesis of globin chains (thaassaemias)
alpha-thalassaemia: reduced production of alpha-globin chains
beta-thalassaemia: reduced beta globin chains
leads to excess of alpha or beta chains - this causes pathophysiology
Qualitative defectsof hemoglobin
Caused by structural defects in globin chains e.g sickle cell disease.
Genetic Disorders of haemoglobin
most common genetic disorder worldwide
Trait thought to give protection from malaria
>1000 genetic mutations described
Sickle Cell Disease being the most clinically significant qualitative defect
HbC,D,E are also common
Frequeuntly get homozygous or compound heterozygotes e.g Hb SC and HbS/beta thal.
Alpha-thalassemia
Traits occur with loss of one / two genes
-Often no anaema, but reduced MCV/MCH/raised RBC
-There are normally 4 copies of the a-genes.
-High prevalence in sub-saharan africa, middle east, india, mediterranean areas, south east asia.
-Clinical severity depending on number of inactive/missing genes.
Alpha thalassaemia - what is Hydrops foetalis?
- alpha-chains essential for both adult and fetal Hb - death in utero occurs if they are absent
A-thalassaemia - Haemoglobin H disease
-Occurs with deletion of 3 alpha - chains
- Excess beta chains form tetramers (B4) known as HbH.
-HbH has a higher oxygen affinity ( do these mutated RBCS get destroyed?.)
-Moderately severe anemia (Hb 7-11 g/dL)
-Microcytic / hypochromic
Englarged spleen (splenomegaly)
Beta Thalassaemia
More than 200 gene mutations
Much more diverse
Wide geographic distribution - Africa, Middle East, Miderterranean areas, South East Asia.
1/4 offpsring if both parents are carriers of the B thalassaemia trait
Excess a-chains responsible for pathology
What are the 3 main categories of Beta Thalassaemia?
B thalassaemia trait (or minor)
B Thalassaemia intermedia
B thalassaemia Major
B Thalassaemia Trait (or minor)
Often asymptomatic or
Mild anaemia/splenomegaly.
B thalassaemia intermedia
More significant clinical problems: anaemia splenomegaly, leg ulcers, bony deformaties.
β Thalassaemia Major (Cooley’s anaemia)
Homozygosity or compound heterozygosity for β thalassaemia.
Ineffective erythropoiesis and a shortened red cell life span.
Severe Anaemia.
Transfusion dependent (iron overload is a problem)
The expansion of haematopoietic bone marrow leads to bony deformities, particularly in the skull and facial bones.
Beta Thalassaemia - Treatment/ Management
Blood Transfusions.
Iron chelation e.g. desferoxamine.
Folic acid supplements.
Splenectomy.
Stem cell transplants in severe forms.
Screening and counselling.
Beta Thalassaemia - Lab investigations
Clinical history/ethnic origin.
FBC (variable).
Reticulocytes.
Blood film (β thal major for example shows target cells, microcytosis/hypochromia, basophilic stippling, teardrop poikilocytosis).
HPLC for quantification of HbA2 and HbF (may be raised).
HbH inclusions.
Ferritin or other tests of iron status.
DNA analysis.
Globin chain studies.
Beta Thalassaemia - Haemoglobin Variants
- Qualitative defects caused by the normal synthesis of an abnormal globin chain.
- Often a single defect in the β-chain e.g. amino acid substitution.
Examples: Haemoglobin S (sickle cell anaemia)
Haemoglobin C, Haemoglobin D, Haemoglobin E, Haemoglobin S/C
Beta Thalassaemia - Haemoglobin Variants - Hemoglobin C
lysine for glutamic acid position 6 on
the β chain
Beta Thalassaemia - Haemoglobin Variants - Hemoglobin D
position 121 glutamine replaces glutamic acid position 121 on the β chain Hb D also known as as Hb D Punjab
Beta Thalassaemia - Haemoglobin Variants - Hemoglobin E
Haemoglobin E: β chain position 26 lysine replaces glutamic acid on the β chain
Sickle Cell Anaemia :
-Form of sickle cell disease (most common)
- Sickle B-globin gene inherited: One from each parent.
- Valine replaces glutamic acid at position 6 of the beta globin chain
Trait : One B-globin gene is inherited (Hb AS)
Sickle Cell Disease
2 β-globin genes are inherited (HbSS).
- Highest incidence in tropical and sub-tropical regions
Predominantly found in people of African and Afro-Caribbean origin.
Protection against malaria.
Common Types of Sickle Cell Disease
Most common are: Sickle Cell Anaemia (SS), Sickle Haemoglobin-C Disease (SC), Sickle Beta-Plus Thalassemia and Sickle Beta-Zero Thalassemia
Pathophysiology of Sickle cell anemia
- Deoxygenated HbS form ‘sickle cells’.
- Deoxygenation causes confirmational changes resulting in insolubility, crystallisation and polymer formation with consequent cell distortion and loss of deformability (sickle cells).
- Results in vaso-occulsion
- Short lifespan results in premature destruction
Clinical features of sickle cell anemia.
- Trait often asymptomatic unless precipitating factor
- Even with HbSS there is variable severity (may be very mild or severe)
- Neonates asymptomatic as mainly HbF (symptoms start about 3-4 months of age)
- May be severe haemolytic anaemia (intravascular & extravascular)
- Painful Vaso-occlusive crisis - Caused by infections, dehydration, acidosis or hypoxia e.g. operations/anaesthesia, altitude, cold weather, extreme exercise
-Dactylitis. - Splenomegaly.
- Neurological problems e.g TIAs, stroke.
- Infections (Aplastic crisis due to parvovirus)
- Priapism.
Treatment of Sickle Cell Anemia
- Avoid factors likely to precipitate crisis e.g. dehydration
- Folic acid
- Good diet
- Hepatitis B, Pneumococcal, Haemophilus and meningococcal vaccinations
- Prophylactic penicillin
- Vaccination and regular oral penicillin
- Crisis – rest, warmth, rehydration, analgesia
- Blood transfusions for severe anaemia and sometimes prophylactic to prevent crisis
- Hydroxycarbamide
- Stem cell transplant
- FBC/blood film
- Automated HPLC for routine screening to detect and quantitate HbS
- Individuals with trait have about 40% HbS
Electrophoresis: CAM electrophoresis at pH 8.4 , Citrate agar electrophoresis at pH 6.2 to separate Hb S, D & G - Hb solubility test
- Prenatal diagnosis / genetic counselling
- NHS Sickle Cell and Thalassaemia Screening Programme
