Haematology/oncology Flashcards
Remind yourself of the structure of fetal Hb
Remind yourself of the structure of adult Hb
- Fetal Hb= 2 alpha, 2 gamma
- Adult Hb= 2 alpha, 2 beta
What is the main/key difference between fetal and adult Hb?
Fetal Hb has higher affinity for oxygen (important as fetal Hb needs to be able to ‘steal’ oxygen from mum’s Hb)
Discuss the transition from fetal to adult Hb
- From 32 weeks of gestation, HbF production decreases and HbA is produced in greater quantities
- At birth, around half of of Hb produced is HbF and half is HbA
- All HbF is replaced by HbA at around 6-12 months of age (except in haemoglobinopathies e.g. some thalassaemias)
Discuss the transition from fetal to adult Hb
- From 32 weeks of gestation, HbF production decreases and HbA is produced in greater quantities
- At birth, around half of of Hb produced is HbF and half is HbA
- All HbF is replaced by HbA at around 6-12 months of age (except in haemoglobinopathies e.g. some thalassaemias)
Most cases of anaemia in infancy are caused by physiological anaemia; what is physiological anaemia?
- At birth, have higher Hb, higher haematocrit and larger RBCs than older children & adults
- Once infant is breathing, there is an increase in oxygenation and hence increase in tissue oxygen level (compared to in utero)
- Results in negative feedback on EPO levels and erythropoiesis
- RBCs of neonate also have shorter life span (90 days)
- Hence, both of the above cause Hb concentration to decrease over first few months of life (around 6-9 weeks)
- It will then remain stable for a few weeks before beginning to rise due to EPO stimulation in the 4th-6th month
*If it occurs in premature babies we call it anaemia of prematurity. Same mechanism as above only their RBCs have even shorter lifespan and they have less EPO production
Other than physiological anaemia of infancy, state some potential causes of anaemia in infants
- Anaemia of prematurity
- Blood loss
- Haemolysis
- Haemolytic disease of newborn (ABO or rhesus incompatibility)
- Hereditary spherocytosis
- G6PD deficiency
- Twin-twin transfusion (blood unequally distributed between twins that share placenta)
Why are premature neonates at higher risk of becoming anaemic?
- Less time in utero receiving Fe from mother
- Reduced EPO levels
- RBC production cannot keep up with rapid growth over first few weeks
- Blood tests remove a significant proportion of their circulating volume
- *The more premature, the more likely they are to require one or more transfusions of anaemia. Becomes even more unlikley if unwell at birth e.g. neonatal sepsis*
- *Same process occurs as in physiological anaemia of infancy but is just enhanced in premature babies due to the above*
Discuss the pathophysiology of haemolytic disease of the newborn
- Lots of different types of rhesus antigens that may or may not be present on RBCs; most important is rhesus D antigen
- Woman may be rhesus D negative but her baby may be rhesus D positive
- Likely that at some point during pregnancy fetal blood will find a way into her blood stream
- Mother will become sensitised to rhesus D antigen (her immune system will recognise it as foreign and produce antibodies)
- Usually, sensitisation doesn’t cause problem in first pregnancy (unless happens early on e.g. in an antepartum haemorrhage)
- During subsequent pregnancies, mother’s anti-D antibodies can cross placenta and if fetus is rhesus D positive then antibodies will attach themselves to fetal RBCs and cause the immune system of the fetus to attack it’s own RBCs
- Leading to haemolysis causing anaemia and high bilirubin (jaundice)
What test can be done to check for haemolytic disease of the newborn?
Direct Coombs test (DCT) -used to check for immune haemolytic anaemia
State 2 common causes of anaemia in older children
State some other rarer causes of anaemia in older children
Common
- Fe deficiency anaemia (most common)
- Blood loss (most frequently in menstruating girls)
Rarer causes
- Sickle cell anaemia
- Thalassaemia
- Hereditary spherocytosis
- Hereditary eliptocytosis
- Sideroblastic anaemia
- Leukaemia
Anaemias can be categories based on RBC size; state 5 causes of microcytic anaemia
*Hint: TAILS
- Thalassaemia
- Anaemia of chronic disease
- Iron deficieny anaemia
- Lead poisoning
- Sideroblastica anaemia (body has Fe available but cannot incorporate it into haemoglobin)
Anaemias can be categories based on RBC size; state 5 causes of normocytic anaemia
*HINT: 3A’s and 2H’s
- Acute blood loss
- Anaemia of chronic disease
- Aplastic anaemia
- Haemolytcia aneamia
- Hypothyroidism
Anaemias can be categories based on RBC size; state 8 causes of macrocytic anaemia- differentiating into megaloblastic and normoblastic macrocytic anaemias
Megaloblastic
- B12 deficiency
- Folate deficiency
Normoblastic
- Alcohol
- Reticulocytosis (usually from haemolytic anaemia)
- Hypothyroidism
- Liver disease
- Drugs e.g. azathioprine
- Pregnancy & neonatal period
State some generic symptoms of anaemia
State 2 symptoms specific to Fe deficiency anaemia
Anaemia symptoms
- Tiredness
- SOB
- Headaches
- Dizziness
- Palpitations
- Worsening of other conditions
Fe Deficiency Anaemia
- Pica
- Hair loss
State some generic signs of anaemia
State some signs that indicate specific causes of anaemia
Generic signs
- Pale skiin
- Pale conjunctiva
- Tachycardia
- Raised RR
Specific signs anaemia
- Fe deficiency: koilonychia (spoon nails), brittle hair & nails, angular chelitis, atrophic glossitis (smooth tongue due to papillae atrophy)
- Haemolytic anaemia: jaundice
- Bone deformities: thalassaemia
What investigations would you do if you suspect a pt has anaemia?
- FBC: haemoglobin, MCV
- Ferritin: Fe deficiency
- TIBC
- Serum Fe
- B12 & folate
- Bilirubin: raised in haemolysis
- Reticulocyte count: check bone marrow response- if high usually indicates anaemia due to haemolysis or blood loss
- Blood film: diagnose G6PD (Heinz bodies, blister cells)
- Direct Coombs test: autoimmun haemolytic anaemia
State 3 reasons for Fe deficiency (not asking for exact causes/disease- just broad reasons but may give examples of diseases); highlight the most common in children
- Dietary insufficiency
- Loss of Fe (e.g. heavy menstruation)
- Inadequate absorption (e.g. Crohn’s disease)
Explain why medications that reduce stomach acid (e.g. PPI’s) can lead to Fe deficiency
Fe mainly absorbed in duodenum or jejenum
Acid is required from stomach to keep Fe in solube ferrous (Fe2+) form
If there is less acidic/environment less acidic then it will change to insoluble ferric (Fe3+) form
It is important to understand tests for Fe deficiency; explain what is meant by:
- TIBC
- Transferrin
- Transferrin saturation
- Ferritin
*Transferrrin is the carrier protein for Fe
- TIBC: space available on transferrin molecules for the Fe to bind
- Transferrin saturation: proportion of transferrin molecules that are bound to Fe (serum Fe/TIBC)
- Ferritin: form Fe takes when deposited and sorted (raised in inflammation)
Why is serum Fe on it’s own not a useful test?
Serum Fe varies significantly throughout day (higher in morning & after eating Fe containing meals)
Explain why a pt with Fe deficiency anaemia may have normal ferritin
- Ferritin released when there is inflammation e.g. infection or cancer
- High ferritin most likely related to inflammation rather than Fe overload
- Pt with Fe deficiency anaemia may have normal ferritin if they have other reasons for raised ferritin e.g. infection
Would the following values be increased or decreased in Fe deficiency anaemia:
- TIBC
- Transferrin
- TIBC: increased (less Fe in body so less bound to transferrin so more space for Fe to bind)
- Transferrin: increased (body tries to compensate for low Fe by making more transferrin to increase carrying capacity)
Would the following values be increased or decreased in Fe overload:
- TIBC
- Transferrin
- TIBC: decreased
- Trasnferrin: decreased
Discuss the management of Fe deficiency anaemia
- Treat underlying cause
- Most common cause is dietary insufficiency hence give oral Fe supplementation (ferrous sulphate or fumarate) and dietician input (NOTE: if due to poor absorption may give IV supplementation)
- Blood transfusion (rarely necessary as children able to tolerate a low Hb well)
For sickle cell anaemia, discuss:
- What it is
- Inheritance pattern
- Mutation
- Genetic condition that results in sickle (crescent) shaped RBCs
- Autosomal recessive
- Substitution of Glu to Val at the sixth amino acid position in the beta-chain hemoglobin; beta globin gene on chromosome 11.
Discuss the pathophysiology of sickle cell disease/why it is a problem
- Polar glutamate replaced with to non-polar valine
- This decreases the water solubility of deoxy-Hb
- Leads to abnormal beta globin chains and abnormal haemoglobin (known as Haemoglobin S)
- Abnormal beta globin chains are prone to polymerising when in the deoxygenated state
- Leads to characteristic sickle shaped RBCs
- Sickled RBCs are more fragile and prone to damage and also lead to further complications e.g.:
- Vaso-occlusive crisis
- Splenic sequestration crisis
- Aplastic crisis
- Acute chest syndrome
Sickle cell trait (where only inherit one mutated gene) results in milder form of sickle cell disease; true or false?
True
- HbAS patients sickle at p02 2.5 - 4 kPa
- HbSS patients at p02 5 - 6 kPa
Explain why sickle cell disease is more common in patients from areas traditionally affected by malaria (e.g. Africa, India, Middle East, Carribean)
- Having one copy of gene (also known as sickle cell trait) reduces the severity of malaria
- Consequently, pts with sickle cell trait more likely to survive in these areas and pass on their genes
- “Selective advantage/natural selection”
When and who do we test for sickle cell disease?
- Pregnant women at risk of having sickle cell gene are offered testing during pregnancy
- Tested for during newborn screening heel prick test
*definitive diagnostic test is Haemoglobin electrophoresis
State some potential complications of sickle cell disease
- Anaemia
- Increased risk of infection
- Avascular necrosis in large joints (e.g. hip)
- Pulmonary hypertension
- Priapism
- CKD
- Sickle cell crisis
- Vaso-occlusive ‘painful’
- Splenic sequestration
- Aplastic
- Acute chest syndrome
- Haemolytic (rare)
Why does sickle cell disease lead to anaemia?
Sickle cells are fragile and more easily destroyed hence lifespan of sickled RBC is ~10-20 days
*NOTE: may also cause more severe anaemia in splenic sequestration crisis and aplastic crisis
State the 5 types of sickle cell crisis
- Vaso-occlusive
- Splenic sequestration
- Aplastic
- Acute chest syndrome
- Haemolytic (rare)
For vaso-occlusive crisis, discuss:
- What causes crisis
- Precipitators (4)
- Presentation
- Management
- Complications
- Sickled RBCs have become stuck and are clogging capillaries causing distal ischaemia
- Maybe precipitated by dehydration, infection, deoxygenation, cold weather (associated with raised hematocrit)
- Presentation:
- Pain (anywhere but usually in bones in arms, legs, spine, chest), fever, priapism, dactylitis, signs of precipitating factor
- Diagnosis= clinical
- Management:
- Analgesia
- Fluids
- High flow oxygen
- Abx if infection suspected
- Priapism= urological emergency (aspiration of blood from penis)
- May get infarcts in various organs including the bones (e.g. avascular necrosis of hip, hand-foot syndrome in children, lungs, spleen and brain)
For splenic sequestration crisis, discuss:
- What causes crisis
- Presentation
- Complications
- Management
- Sickled RBCs blocking blood flow within the spleen causing an acutely enlarged painful spleen
- Presentation: abdo pain, shock
- Complications: severe anaemia, hypovolaemic shock, splenic infarction which results in increased susceptibility to infection
- Management:
- Emergency management: blood transfusions, fluid resuscitation
- Splenectomy prevents sequestration crisis