B5 - Haemolytic anaemia and haemoglobinopathies Flashcards
haemolytic anaemia
- Red cell destruction
○ Increased bilirubin (haem breakdown)
○ Increased LDH - lactate dehydrogenase which is liberated from red blood cells
○ Reduced haptoglobins (Hb-haptoglobin complex) - haptoglobin is consumed when binding with haemoglobin- Evidence of damaged red blood cells
○ Spherocytes
○ Fragmented red blood cells (schistocytes) - occurs in mechanical fragmentation in intravascular haemolysis - Evidence of increased RBC production
○ Reticulocytosis (polychromasia) - typically larger, purple immature cell
○ Nucleated red blood cells - a step in red blood cell maturation prior to reticulocyte (reticulocyte has nucleus extruded)
○ Occurs with normal bone marrow function
- Evidence of damaged red blood cells
clinical features of haemolytic anaemia
- Anaemia - tiredness, fatigue etc.
- Breathless/light headedness
- Jaundice: bilirubin in plasma
- Pigment gallstones (composed primarily of bilirubin) may occur
- Splenomegaly (common)
- Ankle ulcers, usually with people with sickle cell
- Expanded bone marrow - response to blood cell breakdown by increasing erythropoiesis
- Aplastic crises: parvovirus
- Megaloblastic anaemia: folate deficiency (used up)
hereditary causes of haemolytic anaemia
○ Membrane defect: hereditary spherocytosis
○ Enzyme defect: G6PD deficiency
○ Globin chain defect: haemoglobinopathies
acquired causes of haemolytic anaemia
○ Immune haemolytic anaemia ○ Fragmentation haemolysis - thrombotic thrombocytopenic purpura (TTP) ○ Oxidative haemolysis ○ Liver disease (spur cell anaemia) ○ Infections, renal disease, etc.
hereditary spherocytosis
§ Most common inherited haemolytic anaemia
§ Autosomal dominant with variable severity
§ Defect in structural RBC membrane protein
□ Spectrin, ankyrin, band 3
§ RBC less deformable and lose membrane when passing through spleen
□ Lose surface area
§ Red cells become spherical, rigid and then destroyed
§ Fluctuating anaemia and jaundice
§ Splenomegaly and pigment gall stones
hereditary spherocytosis lab features
□ Spherocytes on blood film
□ Polychromasia due to increased reticulocytes (bone marrow response)
□ Negative DAT (direct antiglobulin test)
® Test looking for evidence of immune haemolysis and the presence of antibodies that want to bind red blood cells and destroy them, would be positive in immune haemolysis)
□ Positive EMA (band-3) (probe looking for band 3 protein)
® Flow cytometric test
® Specialised assay that identifies target structures or proteins on cells by creating a fluorescent probe that finds a particular structure
® Eosin-5-malemide binds to band-3 protein
® Probe tends to be reduced or deficient because band-3 is lacking
® Gold standard
direct antiglobulin test
® Test looking for evidence of immune haemolysis and the presence of antibodies that want to bind red blood cells and destroy them, would be positive in immune haemolysis)
EMA (band-3) (probe looking for band 3 protein)
® Flow cytometric test
® Specialised assay that identifies target structures or proteins on cells by creating a fluorescent probe that finds a particular structure
® Eosin-5-malemide binds to band-3 protein
® Probe tends to be reduced or deficient because band-3 is lacking
® Gold standard
treatment for hereditary spherocytosis
□ Splenectomy - if the haemolysis is pronounced, severe cases
□ Folic acid, used to quickly so needs to be replenished otherwise they will have haemolytic and megaloblastic anaemia at the same time
□ Chlocystectomy: removal of the gall bladder to prevent bilirubin gall stones
○ Hereditary Elliptocytosis
§ Autosomal dominant § Milder than HS § Many asymptomatic § Mutations in spectrin § 10% have haemolysis § Elliptical red blood cells § Variants □ Hereditary pyro-poikilocytosis □ South east Asian ovalocytosis
G6PD deficiency
§ Glucose-6-phosphate dehydrogenase deficiency
§ Enzyme in the hexose monophosphate shunt which generated reducing power as NADPH
§ G6PD deficiency: most common red cell enzyme disorder worldwide
§ Gene-X linked chromosome: males more likely to be effected
§ G6PD deficiency
□ RBC susceptible to oxidative stress - causes haemolysis
□ When not subject to oxidative stress, they’ll be fine
□ Triggers of oxidant haemolysis: drugs, fava (broad) beans, infection, hypoxia
□ Intravascular haemolysis (self limiting)
□ Oxidised Hb removed
□ Blood film: bite or blister cells - looks like a bit has been taken out of them due to denatured haemoglobin being removed by macrophages
® Due to oxidative stress denatured haemoglobin (heinz bodies) are formed and macrophages remove them
□ Pooling to one side of the cell - hemighost cells
□ Treatment
® Remove/stop/treat offending agent
® Treat infection
® Transfuse if necessary - most people will not need this
□ Normal blood count between crises
2 enzyme defects leading to haemolytic anaemia
G6PD deficiency, pyruvate deficiency
G6PD deficiency blood film
□ Blood film: bite or blister cells - looks like a bit has been taken out of them due to denatured haemoglobin being removed by macrophages
® Due to oxidative stress denatured haemoglobin (heinz bodies) are formed and macrophages remove them
□ Pooling to one side of the cell - hemighost cells
triggers of oxidation in G6PD enzyme deficiency
drugs, fava (broad) beans, infection, hypoxia
G6PD inheritance
X-linked
Heinz bodies
denatured haemoglobin formed due to G6PD deficiency
pyruvate kinase
§ Glucose is metabolised in RBC by anaerobic glycolysis
§ Embden-Meyerhof pathway
§ Pyruvate kinase is the enzyme that catalyses the final step of glycolysis and is required to make ATP
§ G6PD is more common
pyruvate kinase deficiency
□ Inherited enzyme defect
□ Lack of PK: insufficient ATP made
□ Rigid cell membrane and cell death
□ Haemolytic anaemia
□ Splenectomy partly improves anaemia
□ Autosomal recessive inheritance
□ Variable clinical presentation
® Mild: occasional compensated haemolysis
® Severe: can present in neonatal period with failure to thrive, splenomegaly
□ Prickles on RBC
diagnosing pyruvate kinase deficiency
pyruvate kinase assay
○ Structural haemoglobinopathies
§ Abnormal globin chain structure
§ HbS (sickle cell anaemia); HbE (Thailand); HbC (africa)
Thalassemia
○ Thalassemia
§ Reduced production of a or b globin chains
§ SE Asia (alpha) and Mediterranean (beta)
§ Microcytic anaemias
B thalassaemia
§ Mediterranean or SE Asia § Mutations in the B globin gene § Reduced b chain production § Homozygous (thalassemia major) □ Present at 3-6 months □ Sever anaemia, transfusion dependant, bone marrow transplant § Heterozygous (thalassaemia minor) □ Asymptomatic
A thalassaemia
§ Common in SE Asia
§ 4 a globin genes on chromosome 16 aa/aa
§ Gene deletions 1,2,3, or 4
□ -a/aa and -a/-a thalassaemia minor
□ –/aa thalassaemia minor
□ –/-a haemoglobin H disease
□ –/– Hb barts hydrops fetalis (not compatible with life)
Bart’s hydrous fetalis
§ No a chains
HbS
occurs in African ethnicities
□ HbS forms crystals: sickle shapes RBC
□ Sickling crisis: painful, occluded vessels - happen during low oxygen levels
□ Chest pain, bone pain, tissue infarction, stroke
□ ‘auto-splenectomy’: infarction of spleen - spleen gradually dies off
□ Sickle shapes don’t pass through microvasculature very well
□ Haemolysis - anaemia
○ Structural haemoglobinopathies
Point mutations causing a structural abnormality in a globin chain
HbE
Thailand, target cells, low MCV, common
HbC
west Africa, target cells
auto Immune Haemolytic Anaemia
○ Haemolysis due to antibodies directed at RBC
○ Auto-immune haemolytic anaemia
§ Derived from antibodies made by one’s own body
§ Auto antibody directed at own red blood cells
§ Causes: idiopathic/unknown
§ Disease associations: b cell lymphoma or lymphoid leukemias, autoimmune diseases eg. Lupus
auto immune haemolytic anaemia blood film
§ Blood film
□ Spherocytes and polychromasia due to reticulocytosis on PB film
Presence of nucleated red blood cells and associated disease eg. Leukaemia
auto immune haemolytic anaemia direct anti-globulin test
§ Positive direct antiglobulin test (DAT)
□ Marker of the presence off antibodies that want to bind and destroy red blood cells
□ Blood sample from patient is incubated with antihuman antibodies (Coombs reagent) - if the RBCs agglutinate - this means antihuman antibodies are forming links with antibodies bound to cell surface of RBCs - positive result
auto immune haemolytic anaemia treatment
§ treatment: immunosuppression (corticosteroids to reduce antibody production); treat cause (lymphoma, leukaemia, auto-immune disease), splenectomy in some cases, transfusion may be required if severe
Allo-immune haemolytic anaemia
§ Antibody made by 1 individual reacts with RBC of another (donor)
§ Acute haemolytic transfusion reaction
□ Transfuse wrong/incompatible blood (lab error)
§ Delayed haemolytic transfusion reaction
□ Low level antibody in donor serum not found in testing, driving low level haemolytic reaction over time
§ Haemolytic disease of the newborn
□ Allo-immune haemolytic anaemia
® Transplacental passage of maternal RBC antibodies
® Maternal antibodies destroy fetal RBC
® Doesn’t effect first pregnancy, but will effect second
® Usually Rh(D) negative mother & Rh(D) positive fetus
◊ Anti-D (antibodies) made by mother in first pregnancy when exposed to D antigen
◊ Subsequent pregnancy: maternal anti-D crosses the placenta, binds to and destroys fetal Rh(D) positive RBC
◊ Give anti-D injections to the mother at staggered phases during pregnancy
- Acquired: fragmentation haemolysis
○ Mechanical damage to RBCs
○ ‘Micro angiopathic haemolytic anaemia’ - defect in the blood vessels
§ Red blood cells get damaged as they pass through due to the defect in the blood vessels
§ Any impediment to smooth passage of red blood cells
○ Red cells exposed to an abnormal surface
§ Small blood vessels
§ Heart valve, pinhole lesion in heart
§ Fibrin strands in the vasculature
§ Damaged small blood vessels
§ Any impediment to smooth passage of red blood cells
○ Red cell fragmentation
§ Leads to anaemia
§ Schistocytes (fragments) on film
§ Intravascular haemolysis (inside BV)
‘Micro angiopathic haemolytic anaemia’
defect in the blood vessels
§ Red blood cells get damaged as they pass through due to the defect in the blood vessels
§ Any impediment to smooth passage of red blood cells
- Other Acquired Haemolytic Anaemia
○ Liver disease (spur cell anaemia) and renal failure alter the RBC membrane
○ Infections: can be inside RBC eg. Malaria (malarial parasites like to live inside RBC)
○ Infections and haemolytic anaemia
§ Severe bacterial sepsis
□ Disseminated intravascular coagulation which results in microangiopathic haemolytic anaemia
§ Malaria
§ Clostridium welchii
□ Spherocytic
