Where is erythropoietin (EPO) produced and why?
Produced in the kidneys in response to tissue O2 concentration.
What are the various types of normal haemoglobin?
Hb-A = 2alpha/2beta
Hb-F = 2alpha/2gamma
HbA2 = 2alpha/2delta
All normal Hb have 2 alpha and 2 non-alpha chains
The gene for alpha globin is on which chromosome?
The genes for gamma, delta and beta haemoglobins is on which chromosome?
What percentage of a normal adult's Hb is Hb-A?
What percentage of a normal adult's Hb is Hb-A2?
What percentage of a normal adult's Hb is Hb-F?
What are the haemoglobinopathies?
Structural Hb variants - eg HbS (Sickle), C, D, E etc, usually a single base substitution in globin gene = altered structure/function
Thalassemias (alpha or beta) - change in globin gene expression leads to reduced rate of synthesis of NORMAL globin chains. Pathology is due to imbalance of alpha and beta chain production (free globin chains damage red cell membrane)
Why might physiological anaemia and macrocytosis occur during pregnancy?
Plasma volume expands in pregnancy by 50%.
Red cell mass expands by 25%
Haemodilution occurs, maximally at 32 weeks
CDC define anaemia as Hb <11g/dL 1st and 3rd trimester and <10.5 in the 2nd trimester
What are the features of obstetric leukocytosis?
Mainly a neutrophilia, rising from the 2nd month to a peak range of around 9-15 in the 2nd-3rd trimester
Left shift may also be seen (myelocytes/metamyelocytes)
What are the features of gestational thrombocytopenia?
Platelet count usually >70x10^9/l
Platelet count falls after 20weeks and thrombocytopenia is most marked in late pregnancy
No pathological significance for mother or fetus
Recovers rapidly following delivery
Main issue in management is differentiation from other causes
What are the pregnancy-associated causes of thrombocytopenia?
Production failure: - severe folate deficiency
- Pre-eclampsia and HELLP syndrome
- DIC eg in abruption
What are the coincidental causes of thrombocytopenia?
Production failure: - bone marrow infiltration/hypoplasia
ITP: primary/secondary -
Viral (HIV, EBV)
Sepsis Type 2B vWD
Why is pregnancy a pro-thrombotic state?
Evidence of platelet activation
Increase in many procoagulant factors
Reduction in some natural anticoagulants
Reduction in fibrinolysis
Rise in markers of thrombin generation
Rise in certain coagulation factors
What is the test of choice for diagnosing structural Hb abnormalities?
What are the microscopic features of thalassemic RBCs?
Small pale red cells (hypochromic/microcytic)
What battery of tests is performed for the diagnosis of haemoglobinopathies?
High performance liquid chromatography (HPLC)
Heat stability, isopropanol (unstable Hb’s)
Oxygen dissociation curve (p50, high affinity)
DNA analysis (genetic counseling, prenatal Dx)
Kleihauer testing, Supravital staining, Sickle solubility
What is the the molecular basis of sickle cell disease?
- valine substituted for glutamine at position 6 of the β-globin gene
Why does the RBC 'sickle' in sickle cell disease?
Sickle Hb (Hb-S) polymerises at low oxygen tensions to form long fibrils (“tactoids”) which distort the red cell membrane and produce the classical sickle shape.
Why do the sickle cells have a short lifespan?
What is haemolysis-associated haemostatic activation?
- Intravascular haemolysis releases Hb into plasma which quenches NO and generates ROS - The depletion of NO is associated with pathological platelet activation and tissue factor expression
What is sickle cell trait?
Hb Electrophoresis: Hb-S 45%, Hb-A 55%
What is sickle cell disease?
Blood count: anaemia (Hb 6-8g/dl)
Blood film: sickle cells
Hb Electrophoresis: Hb-S >95%, Hb-A 0%
Frequency: 1 in 200 African-Caribbeans, 1 in 60 West Africans
What are the acute complications of sickle cell disease?
Vaso-occlusive crisis - hands and feet (dactylitis), chest syndrome, abdominal pain (mesenteric), bones (long bones, ribs, spine), brain, priapism
Sequestration crisis (spleen, liver)
What are the chronic complications of sickle cell disease\/
- Hyposplenism - due to infarction and atrophy of spleen.
Renal disease: medullary infarction with papillary necrosis. Tubular damage - can’t concentrate urine (bed-wetting at night).
Glomerular – chronic renal failure/dialysis
Avascular necrosis (AVN) –femoral/humeral heads
Leg ulcers, osteomyelitis, gall stones, retinopathy, cardiac, respiratory
Mortality: ~ 0.5% per annum in UK
Why would you transfuse a sickle cell patient?
- Top up: splenic sequestration, aplastic crisis, pre-operative, acute chest crisis (usually when Hb <5g/dl)
What is the function of hydroxycarbamide and why would it be used?
Increases Hb F (time delay to polymerisation, reduced adhesion to endothelium, enhances NO)
Consider if >3 admissions with painful crisis in 12 months or 2 chest crisis (MSH study 1995)
What are the curative treatments for sickle cell disease?
Bone marrow transplant from normal donor
What perioperative care is required for people with sickle anaemia?
Avoid local tourniquet
What are the other possible causes of sickle cell disease?
Co-inheritance of βs and another β chain abnormality
SC disease – fewer crisis, risk AVN and retinopathy
S/β-thalassaemia, S/Lepore, S/D-punjab (moderate)
S/HPFH, S/δβ0, S/E (mild)
How are the thalassemias classified?
Divided into α, β, δβ and γδβ according to which globin chain is reduced.
What is alpha thalassemia?
Results from one or more defective alpha globin genes.
What are the different types of Alpha thalassemia?
Alpha thalassemia minima: only one allele affected, minimal pathology
Alpha thalassemia minor: two alleles affected but still almost normal production of RBCs. Mild microcytic hyperchromatic anaemia.
Haemoglobin H disease: two unstable haemoglobins are present in the blood: Haemoglobin Barts (tetrameric γ chains) and Haemoglobin H (tetrameric β chains). Both of these unstable haemoglobins have a higher affinity for oxygen than normal haemoglobin, resulting in poor oxygen delivery to tissues.
Alpha thalassemia major: Foetuses are oedematous and have little circulating hemoglobin, and the haemoglobin that is present is all tetrameric γ chains (also called haemoglobin Barts). When all four alleles are affected, the foetus likely will not survive gestation without in utero intervention: most infants with alpha thalassemia major are stillborn with hydrops fetalis, and those who do not receive in utero treatment and are born alive die shortly after birth.
What is beta thalassemia?
Reduced rate of production of beta-globin chains (pathology caused by excess alpha chains)
Many molecular variants arising in different locations worldwide
Carriers (Thalassaemia Minor) are clinically normal
Homozygotes (Thalassaemia Major) have a severe disease which is usually fatal if untreated – can produce little, if any, Hb-A and die of severe anaemia
What are the microscopic features of beta thalassemia minor?
Blood picture resembles iron deficiency (small, pale red cells)
Total Hb level normal or only slightly reduced
Hb-A2 level >3.5% - “target cells” on film
What are the features of beta thalassemia intermedia?
Bone changes and osteoporosis
Endocrine and fertility (DM, Hypothyroid)
What are the features of beta thalassemia major?
present with very severe anaemia at 1 to 2 years of age
blood film very abnormal with lots of nucleated red cells
clinical features due to severe anaemia and attempt to make more red cells in marrow to compensate
Describe the pathology of beta thalassemia major.
Alpha chain excess - ineffective erythropoiesis, shortened RBC lifespan (haemolysis) = anaemia
Increased marrow activity - skeletal deformity, stunted growth, increased iron absorption and organ damage (exacerbated by blood transfusion), protein malnutrition
Enlarged and overactive spleen - pooling of red cells (increased anaemia), increased tranfusion requirement
Short stature and distorted limb growth due to premature closure of epiphyses in long bones
Enlarged liver and spleen “extramedullary haemopoiesis”
What are thalassaemic facies?
Frontal bossing due to expanded bone marrow
What is a classic feature of beta thalassemia seen on x-ray?
“hair on end” skull due to widening of diploic cavities by marrow expansion
How is transfusion a useful treatment for beta thalassemia major?
to maintain mean Hb 12g/dl (pre-transfusion Hb 9.5-10)
suppresses marrow red cell production and prevents skeletal deformity and liver/spleen enlargement
3 to 4 weekly transfusions from 1st year of life
What are the problems associated with treating beta thalassemia with transfusion?
each unit of red cells contains 200-250mg Iron and the body has no excretory mechanism for iron
by 10-12 years of age there is severe iron overload and toxicity: gonads/hypothalamus – failure of puberty, growth failure, pancreas – diabetes, heart – dilated cardiomyopathy and heart failure, liver - cirrhosis
What are the top five causes of death in thalassemia?
1. Heart failure
How is death from iron overload prevented in patients with beta thalassemia?
Iron chelation therapy from 2nd year of life
Desferrioxamine is given by 8-12 hourly subcutaneous infusion via a syringe-pump as home-treatment on at least 5 nights a week to prevent the accumulation of iron
New Oral Iron Chelators include Deferiprone and Deferasirox
How is bone health maintained in patients with beta thalassemia?
Timely transfusion, no over-chelation, diet, hormone replacement of hypogonadism, monitoring for OP, treatment with bisphosphanates
How is fertility maintained in patients with beta thalassemia?
Good chelation, fertility clinic advice, may need induction.
Cardiac, thyroid, diabetic and bone assessments.
What is the cure rate for bone marrow transplantation for patients with beta thalassemia?