Haemolytic Anaemias Flashcards
What is anaemia?
A reduced haemoglobin level for the age and gender of the individual
What is haemolytic anaemia?
anaemia due to shortened RBC survival
Describe the variation in blood haemoglobin concentration throughout life
Babies when they’re born have HbF which is very high in concentration [180-190 g/dl] which falls in the first few months of life
Children have lower Hb than adults and females have lower Hbs than men
Where are RBCs produced?
RBCs produced in bone marrow along with all the factors required for their production (iron, B12/folate, Globin chains, protoporphyrins to carry haem)
What stimulates RBC growth?
Erythropoietin (EPO hormone) signals RBC production
How are RBCs released into circulation?
RBCs lose their nucleus as they exit bone marrow into circulation where they survive for ~120days
What is the fate of RBCs after 120 days?
As RBCs mature, changes occur to their red cell membranes identified by macrophages in the liver & spleen. These organs remove the older RBCs from circulation
Describe the structure of mature RBCs in circulation
Seen in peripheral circulation
Biconcave disc shape; comply able to fit through small capillaries
What are the metabolic pathways taking place within RBCs?
- glycolytic pathway
- hexose-monophosphate shunt
What is the role of the metabolic pathways in RBCs?
Hb delivers O2 to tissues
Metabolic pathways maintain energy in RBC and keep it running
What is the consequence of incorrect functioning of RBC metabolic pathways?
Problems with these factors or external factors can reduce no. of RBCs
What is haemolysis?
Destruction of RBCs
How odes haemolysis affect the lifespan of RBCs?
Shortened red cell survival 30 - 80 days
How does the bone marrow compensate for haemolysis?
Bone marrow compensates with increased EPO ⇒ increased red blood cell production
What effect does haemolysis have on RBCs in circulation?
Increased young cells in circulation = Reticulocytosis +/- nucleated RBC
What is compesated haemolysis?
RBC production able to compensate for decreased RBC life span = normal Hb
What is Incompletely compensated haemolysis?
RBC production unable to keep up with decreased RBC life span = decreased Hb
Describe the clinical findings of haemolysis
- Jaundice (unconjugated bilirubin)
- Pallor/fatigue
- Splenomegaly
- Dark urine
- Haemolytic crises-increased anaemia and jaundice with
infections/ precipitants - Aplastic crises-anaemia, reticulocytopenia with parvovirus
infection
(causes rash & red cheeks, affects erythroblasts)
What are the chronic clinical findings of haemolysis?
- Gallstones; pigment due to breakdown of bilirubin
- Splenomegaly; abnormal RBCs detected by
macrophages from the spleen - Leg ulcers (Nitric Oxide scavenging)
- Folate deficiency (increased use to produce more RBCs)
Describe the clinical findings of haemolytic anaemia identified in the lab?
- Increased reticulocyte count
(exceptions: parvovirus / an inability to produce RBCs) - Increased unconjugated bilirubin
- Increased LDH (lactate dehydrogenase)
- Low serum haptoglobin (protein that binds free
haemoglobin) - Increased urobilinogen
- Increased urinary haemosiderin
(Fe from Hb picked up by urinary tract epithelial cells,
excreted in urine) - Abnormal blood film
What is a blood film?
A thin layer of blood smeared on a glass microscope slide and then stained in such a way as to allow the various blood cells to be examined microscopically
What blood film stain allows us to the reticular network?
Supravital stain used to see reticular network
What are polychromatic cells?
olychromasia is a disorder where there is an abnormally high number of immature red blood cells found in the bloodstream as a result of being prematurely released from the bone marrow during blood formation
Describe the blood film of polychromatic cells
These cells are often shades of grayish blue
What are poikilocytes?
abnormally shaped RBCs
their shape helps identify cause
Summarise the clinical features of haemolytic anaemia
Jaundice Pallor Splenomegaly Pigment gallstones (chronic) Risk of aplastic crisis from parvovirus B19
Summarise the lab findings of haemolytic anaemia
Normal/ low haemoglobin Reticulocytosis +/- NRBC Raised LDH Raised unconjugated bilirubin Decreased haptoglobin Increased urobilinogen +/- haemoglobinuria Abnormal blood film
How is haemolytic anaemia classified?
Anaemia may be classified by
Inheritance
- genetic or acquired
Site of RBC destruction
- intravascular or extravascular
Origin of RBC damage
- intrinsic or extrinsic
Give an example of a inherited and acquired haemolytic anaemia
Inherited: Hereditary spherocytosis
Acquired: Paroxysmal noctural haemoglobiuria
Name haemolytic anaemias based on their site of RBC destruction
Intravascular: thrombotic thrombocytopenic purpura
Extravascular: Autoimmune Haemolysis
Give examples of haemolytic anaemias depending on the origin of RBC destruction
Intrinsic: G6PD
extrinsic: delayed haemolytic transfusion reaction
How do inherited haemolytic anaemias cause haemolysis?
Hereditary anaemias affect RBC membranes or enzyme function (G6PD etc.)
What are the inherited types of haemolytic anaemia?
Membrane Disorder
- Spherocytosis
- Elliptocytosis
Enzyme Disorders
- G6PD deficiency
- Pyruvate Kinase Deficiency
Haemoglobin DIsorders
- Sickle Cell Anaemia
- Thalassaemia
What are the acquired haemolytic anaemias?
Immune Drugs Mechanical Microangiopathic Inections Burns Paroxysmal Nocturnal Hemoglobinuria
What is the most common site of RBC destruction?
Most commonly extravascular haemolysis
Outline how extravascular haemolysis occurs
- Macrophage engulfs and destroys abnormal RBC into its
constituents - Bilirubin excreted, Fe stored and released back into
liver where globin chains are degraded into amino acids
Explain what occurs in intravascular haemolysis
Intravascular haemolysis
RBC not systematically broken down: all Hb released and pre-Hb in blood and urine
Describe the normal red cell membrane structure
Lipid bilayer
Integral proteins anchor membrane to cytoskeleton
Outline the protein defects in hereditary spherocytosis
Defects in vertical interaction (hereditary spherocytosis) - Spectrin - Band 3 - Protein 4.2 - Ankyrin
Describe the protein defects in hereditary elliptocytosis
Defects in horizontal interaction (hereditary elliptocytosis) - Protein 4.1 - Glycophorin C - (Spectrin – HPP)
What is the inheritance pattern for membrane disorders?
Most of these disorders are autosomal dominant, phenotypes run in families
What are spheorcytes?
Problems with vertical anchors = spherocytes
What are elliptocytes?
Horizontal stabilities = elliptocytes as cells elongate
Describe the features of hereditary spherocytosis
Common hereditary haemolytic anemia
- Inherited in autosomal dominant fashion (75%)
- Defects in proteins involved in vertical interactions
between the membrane skeleton and the lipid bilayer
- Decreased membrane deformability
- Bone marrow makes biconcave RBC, but as they
circulate membrane is lost, the RBC become spherical
How would a blood film differ between normal and spherocytosis RBCs?
Central pallor seen on blood film in normal RBCs
Spherocytosis blood film shows rounder RBCs with no central pallor and some polychromatic cells
How is hereditary spherocytosis diagnosed?
Diagnose using DAT (direct antiglobulin test): identifies Ab on RBC membrane
-ve in hereditary spherocytosis
+ve in autoimmune haemolysis
Outline the clinical features of hereditary spherocytosis
- Asymptomatic to severe haemolysis
- Neonatal jaundice
- Jaundice, splenomegaly, pigment gallstones
- Reduced eosin-5-maleimide (EMA) binding – binds to
band 3 membrane protein - Positive family history
- Negative direct antibody test
How is Hereditary spherocytosis managed?
Monitor
Folic acid
Transfusion (~1-2%)
Splenectomy
What are enzymopathies?
Defects within RBC Metabolic Pathways
What is the significance of glycolysis?
Glycolysis required for energy- ATP
Na/K pump
3 Na+ out 2 K+ in
ATP ADP+Pi
What is the significance of the hexose monophosphate shunt?
HMS – reducing power -NADPH/GSH
What is the isgnificance of the 2,3 BPG pathway?
2,3 Bi-PhosphoGlycerate (2,3 BPG) – modulates O2 binding to Haemoglobin
What are the most common enzyme abnormalities?
G6PD
Pyruvate Kinase
What is the role of the HMP shunt?
Role of the HMP shunt:
- Generates reduced glutathione
- Protects the cell from oxidative stress
When do G6PD patients experiece problems?
G6PD patients RBCs are normal but when exposed to oxidative stress can cause problems
What are the effects of oxidative stress on G6PD patients
- Oxidation of Hb by oxidant radicals
- Resulting denatured Hb aggregates & forms Heinz
bodies; bind to membrane - Oxidised membrane proteins; reduced RBC deformability
Describe the inheritance pattern of G6PD
Hereditary, X-linked disorder
Common in African, Asian, Mediterranean and Middle Eastern populations
Mild in African (type A), more severe in Mediterraneans (type B
Clinical features range from asymptomatic to acute episodes to chronic haemolysis
What are teh oxidative precipitants of G6PD pateints
Oxidative Precipitants Infections Fava/ broad beans Many drugs Dapsone Nitrofurantoin Ciprofloxacin Primaquine
Name examples of oxidative precipitant drugs
- Dapsone
- Nitrofurantoin
- Ciprofloxacin
- Primaquine
Describe the blood film of G6PD patients
Bite cells were chunks have been taken out of RBCs
Blister cells & ghost cells from where membranes have blistered away from Hb
Heinz bodies (methylene blue)
Why may an enzyme assay of a G6PD patient come back normal?
Reduced G6PD activity on enzyme assay
May be falsely normal if reticulocytosis
What is the significance of pyruvate kinase?
PK required to generate ATP
Essential for membrane cation pumps (deformability)
Describe the inheritance pattern of PKD
Autosomal recessive (rarer)
What are the effects of PKD ?
Chronic anaemia
Mild to transfusion dependent
Improves with splenectomy
Describe the blood film of PKD patiets
Blood film shows prickle cells - RBCs with pricks coming off the surface
Polychromasia also visible
Describe the normal structure of Haemoglobin
Haem = Fe2+ ad protoporphyrin IX
Globin (protein)
2alpha and 2beta globin chains
What is the normal Hb composition in adults?
There are alpha-like and beta-like chains
Lots of HbA (2alpha, 2beta) - adult Hb Some HbA2 (2alpha 2delta)
Describe the structure of foetal Hb
Foetal Hb is designed to extract O2 from placenta rather than air and consists of 2alpha, 2gamma chains
What is the Hb composition at birth
When you’re born Hb consist of ~20-30% HbA and rest is HbF
What is the composition of Hb during early embryonic life?
During early embryonic life we mostly require alpha chains, beta chains are produced mainly postnatally
Which Hb globin chain defects is responsible for most haemoglobinopathies
Haemoglobinopathies usually due to problems with beta chains so patients are fine during neonatal period
Give an example of a alpha chain pathology
Alpha thalassemia 0 which causes problems in utero
What are the two types of causes of haemoglobinopathies?
- Quantitative
- Qualitative
What are quantitative haemoglobinopathies?
Quantitative - thalassaemias:
Production increased/ decreased amount of a globin chain (structurally normal)
What are qualitative haemoglobinopathies?
Qualitative – variant haemoglobins:
Production of a structurally abnormal globin chain
What are the features of sickle cell?
HbS: autosomal recessive
sickle cell point mutations cause Hb changes
RBCs polymerise producing long spindly cells rather than normal round RBCs
What are the features of Hb Koln?
Hb Koln: autosomal dominant
Alters Oxygen binding and becomes unstable
What are the features of HbC?
HbC: autosomal recessive, RBCs crystalise
What are thalassaemias?
Imbalanced alpha and beta chain production; too much of one causes issues
Why are excess unpaired Hb globin chains problematic?
- Precipitate and damage RBC and their precursors
(erythroblasts) - Ineffective erythropoiesis in bone marrow
- Haemolytic anaemia
Which is the most common of the thalassaemias
Beta thalassaemia
Describe the inheritance pattern of beta thalassaemia
Autosomal recessive: both parents would carry thalassaemia trait (small RBCs, low MCV) but are fine
¼ chance of having a child with both mutations
How can parents detect if their baby will be a carrier of thalassaemia?
Antenatal screening offered in UK - blood test carried out to assess if baby is a carrier - can get prenatal diagnosis
How is SCA tested in babies?
All babies are tested for SCA using a newborn blood spot which also detects thalassaemia
Describe the blood film of a transfused patient
Normal RBCs as well as abnormal RBCs with precipitated Hb and ghost cells
Describe the symptoms used to diagnose thalassaemia trait
- Asymptomatic
- Microcytic hypochromic anaemia
- Low Hb, MCV, MCH
- Increased RBC
- Often confused with Fe deficiency
- Compensatory increased HbA2; more delta chains in β-
thal trait – (diagnostic) - a-thal trait often by exclusion
- Globin chain synthesis (rarely done now)
- DNA studies (expensive)
Why is beta thalassaemia major so dangerous in children?
As children stop producing HbF and are unable to form correct HbA thalassemia patients become increasingly anaemic
What are the effects of beta thalassaemia major?
Patients still try making Hb but it isn’t picked up so get enlarged spleen and liver
Transfusion dependent in 1st year of life
What are the consequences of beta thalassaemia major if patients aren’t transfused?
If not transfused:
- Failure to thrive
- Progressive hepatosplenomegaly
- Bone marrow expansion; skeletal abnormalities
- Death in 1st 5 years of life from anaemia
What are the side effects of transfusion in beta thalassaemia major patients?
Iron overload
- Endocrinopathies
- Heart failure
- Liver cirrhosis
What causes SCA?
Different combinations of genetic mutations can cause SCA
e. g. Clinically significant sickling syndromes:
- HbSS
- HbSC
- HbS-D Punjab
- HbS- O Arab
- HbS- β thalassaemia
Outline how SCA arises
- point mutation in Beta globin gene: glutamic acid ->
valine - insoluble Hb tetramer when deoxygenated ->
polymerisation - sickle cell shaped cells
Describe the pathophysiology of SCD
SCD causes a huge spectrum of problems due to intravascular haemolysis causing changes to NO
RBCs have abnormal membranes which alters the vasculature
What are the acute complications of haemolytic anaemias?
- Stroke: ischaemic + haemorrhagic
- cholecystitis
- hepatic sequestration
- dactylitis
- bone pain + infarcts
- osteomyelitis
- retinal detachment
- vitreous haemorrhage
- chest syndrome
- splenic sequestration
- haematuria papillary necrosis
- priapism
- aplastic crisis
- leg ulcers
Outline the chronic complications of haemolytic anaemias
- silent infarcts
- pulmonary hypertension
- chronic lung disease, bronchiectasis
- erectile dysfunction
- chronic pain syndromes
- Azoospermia
- delayed puberty
- moya-moya
- retinopathy, visual loss
- chronic renal failure
- avascular necrosis
- leg ulcers
What are the clinical features of SCD?
Painful crises
Aplastic crises
Infections
Outline the acute sickling features
Acute sickling:
- Chest syndrome
- Splenic sequestration
- Stroke
Outline the chronic sickling effects
Chronic sickling effects:
- Renal failure
- Avascular necrosis bone
What are the lab features of SCD?
Anaemia Hb often 65-85 Reticulocytosis Increased NRBC Raised bilirubin Low creatinine
How is SCD diagnosis confirmed?
Solubility test
Expose blood to reducing agent
Hb S precipitated
Positive in trait and disease
electrophoresis to confirm
HPLC is not definitive – need sickle solubility test
What are the 2 types of immune haemolysis?
- autoimmune
- alloimmune
What are the causes of autoimmune haemolysis?
Autoimmune (immune / ab mediated) - ab produced against own cells
Idiopathic
- Usually warm
- IgG, IgM
Drug-mediated (mainly antibiotics)
Cancer associated
- LPDs
What are the causes of alloimmune haemolysis?
Alloimmune
Transplacental transfer:
- Haemolytic disease of the newborn: D, c, L
- ABO incompatibility
Transfusion related
- Acute haemolytic transfusion reaction; ABO
- Delayed haemolytic transfusion reaction E.g Rh groups,
Duffy
Give examples of non-immune acquired haemolysis
- Paroxysmal nocturnal haemoglobinuria
- fragmentation haemolysis
What is paroxysmal nocturnal haemoglobinuria
Red cells have proteins protecting them from complement mediated lysis
Acquired mutations in these cause cells to become vulnerable to complements within the plasma causing lysis → haemoglobinuria; intravascular haemolysis
What is fragmentation haemolysis?
Red cell fragments on blood film due to: Mechanical Microangiopathic haemolysis - Disseminated intravascular coagulation - Thrombotic thrombocytopenic purpura
What other ways can we acquire haemolysis?
Severe burns
Some infections: e.g. malaria
