Haematology Flashcards
What does normal adult Hb consist of? (HbA)
4 globin chains- 2 alpha and 2 gamma
4 haem molecules - one in each chain
In what chain is there a mutation that leads to sickle cell?
Beta chain
What is part of the clinical syndrome of sickle cell disease?
Painful crises
Systemic vasculopathy
End organ damage
Reduced life expectancy
What is the pathology behind thalassemia?
Reduced or absent production of beta or alpha chains leading to imbalance in the chains - ineffective erythropoiesis
What clinical features may be seen in thalassemia?
Effects of anaemia
Effects of iron overload in those with many transfusions
What is the genetic mutation that occurs in sickle cell disease?
Substitution of glutamate by valine in position 6 of the beta globin chain
What mode of inheritance is sickle cell disease?
Autosomal recessive
Do people who are sickle cell carriers experience symptoms?
No
What is the pathophysiology of sickle cell disease?
Polymerisation of the haemoglobin leads to deoxygenation and dehydration and sickling of the RBC leading to vaso-occlusion, infarction and haemolyisis
What are precipitating factors for a sickle cell crisis?
Hypoxia High HbS concentration (possibly via dehydration) Acidosis Infection Skin cooling Stress
What complication can arise post reperfusion after a sickle cell crisis?
Free radical damage
What are positive lab findings in sickle cell disease?
Anaemia
Haemolysis- high bilirubin, high LDH, high reticulocytes and undetectable haptoglobin
Blood film showing sickle cells
Hb electrophoresis
Hb solubility test - turns opaque if positive
What are the emergency presentations of sickle cell disease?
Acute chest syndrome Overwhelming sepsis Painful acute crisis Acute deterioration of anaemia (aplastic crisis or sequestration) Acute visual loss Priaprism Renal impairment Acute chest syndrome Fat embolism syndrome/ multi organ failure Stroke
How does a sickle cell crisis present?
Rapid onset bone pain due to bone marrow infarct
Variable severity and duration - can last hours to weeks
Fever and bone tenderness
+- swelling, hypertension, tachycardia, tachypnoea
How is a sickle cell crisis managed?
Adequate prompt analgesia (usually parental opiates)
Fluids
How is acute chest syndrome defined?
Acute illness
New infiltrate on CXR
Respiratory symptoms
When is acute chest syndrome more likely?
Surgery/anaesthesia
Pregnancy
What are complications from acute chest syndrome?
Increased risk of chronic lung disease and death
What is the pathophysiology of acute chest syndrome?
Infection, asthma and hypoventilation leading to hypoxia, inflammation and acidosis
Fat emboli and pulmonary thrombi leading to increased vaso occlusion within pulmonary microvasculature
Creates a vicious cycle
What is the immediate management of acute chest syndrome?
Adequate analgesia Incentive spirometry O2 therapy Non invasive ventilation even in the absence of severe hypoxia Fluids Antibiotics Transfusion
Why do sickle cell patients get overwhelming hypo splenic sepsis?
Splenic autoinfarction from a very young age leading to functional asplenia
What pathogens lead to overwhelming hypo splenic sepsis?
Pneumococcal
Meningococcal
H.influenzae
What age does hypo splenic sepsis typically occur?
Over 3 years
What is the mortality of splenic sepsis?
50 percent in fulminant disease
What are the symptoms of overwhelming splenic sepsis?
Febrile, coma, altered sensorium, seizures
What is the treatment for overwhelming splenic sepsis?
Urgent antibiotics
Prophylactic penicillin V
What can be done as prophylaxis in overwhelming splenic sepsis?
Prophylactic penicillin V
Vaccination
What are the signs and symptoms of sequestration?
Painful enlargement of the spleen
Drop in Hb of 2g per litre or more
High reticulocytes
What is the mortality from sequestration?
12 percent
What is the recurrence rate of sequestration?
50 percent
What percentage of sequestration cases occur in children under 2?
78 percent
What virus causes an aplastic crisis?
HPV B19 (common childhood illness)
What diseases are caused by HPV B19?
5th disease
Slapped cheek disease
What is the pathophysiology of an aplastic crisis?
Infection of red cell precursors in the marrow leading to pre red cell aplasia - giving low reticulocytes
What can be seen on blood tests with aplastic crisis?
Hb nadir 15 days post infection
What is the management of an aplastic crisis?
Urgent blood transfusion
Which chromosomes are effected in beta thalassemia?
11 and 16
What is the pathophysiology of beta thalassemia?
Lack of production of beta chains so increased alpha chain inclusion which is toxic to red cell progenitors
Leads to ineffective erythropoiesis
What is the clinical syndrome of beta thalassemia?
Severe anaemia - leads to growth failure and plasma volume expansion (probably leading to worsening anaemia)
Bone marrow expansion - gives thalassemia facies and hairy skull on X-ray, also causes bone disease, poor dentition and extramedullary erythropoiesis
What is the prognosis of beta thalassemia?
Death in first to second decade without transfusion
How is beta thalassemia managed?
Regular transfusions to maintain Hb over 10/dl
Be aware of iron overload (haemosiderosis)
What is the clinical sequelae of iron overload?
Cardiac failure Arrhythmia Cardiomyopathy Pituitary - impaired growth and infertility Hypoparathyroidism Hepatic cirrhosis Hypogonadism DM
How can iron status be assessed?
Serum ferritin - although is an acute phase reactant so non specific
TIBC
Liver biopsy - invasive
Cardiac and liver MRI (gold standard)
What is the gold standard way of assessing iron status?
Cardiac and liver MRI
How does liver MRI grade iron status?
Liver (mg/g dry weight)
Normal15
How does a cardiac MRI grade iron status?
Cardiac (msec)
Normal >20
Moderate 10-20
Severe
Name some iron chelation agents?
Desferoxamine (continuous infusion)
Deferiprone (oral)
Deferassirox (oral)
Which features in the history may point to iron overload?
Short stature Splenectomy Osteoporosis Amenorrhoea Hair loss
How many alpha globin chains does a normal person have?
4, 2 from each parent
What is the pathophysiology in alpha thalassemia?
Reduced production of alpha chains so increased beta chains but these are less toxic that increased alpha chains
What different genotypes are relevant to alpha thalassemia?
Normal - 2 alpha on each chromosome
Silent carrier - single alpha deletion on one chromosome
Alpha plus thalassemia trait - single alpha deletion on each chromosome
Alpha 0 thal trait - double alpha deletion on one chromosome
What is HbH?
Beta tetramers- non functional
What is HbBarts?
Y tetramers
Which ethnic groups are high risk for Alpha 0 thalassemia?
China
South East Asia
East Mediterranean
Middle East
What is the clinical syndrome of alpha thalassemia trait?
Asymptomatic
Low or very low MCV/MCH with no evidence or iron deficiency
Definitive diagnosis with genetic testing
What mode of inheritance is alpha thalassemia?
Mendelian codominant
What happens in the event of homozygous alpha 0 thalassemia?
Incompatible with life
Hydrops fetalis
What is the genotype for HbH disease?
A single alpha deletion on one chromosome with a double alpha deletion on the other
What are the clinical features of HbH disease?
Microcytic/hypochromic anaemia of variable severity
HbH inclusion bodies
Tendency for iron overload
What is the clinical picture for thalassemia intermedia?
Significant anaemia but not transfusion dependent
Increased iron absorption so risk of iron overload disproportionate to transfusion history
What are common examples of thalassemia intermedia?
- Beta thal major with alpha thal trait so less beta and alpha imbalance
- Beta thal trait with triplicate alpha chains so more alpha and beta imbalance
What is the purpose of heel prick antenatal screening test?
To identify significant haemoglobinopathy including sickle cell and offer penicillin prophylaxis, immunisation and parent education
How much haemoglobin is made daily and lost daily?
1ml made, 1ml lost
What can cause a normocytic anaemia?
Haemolytic Bone marrow disorder Hypersplenism Acute blood loss Anaemia of chronic disease
What can cause a macrocytic anaemia?
B12 and folate deficiency
Liver disease
Hypothyroidism
Reticulocytosis
What can lead to normocytic anaemia with a high Hct?
Thalassemia