Sickle cell & thalassaemia flashcards
13 high-yield MRCP Part 1 cards from the Intellect Medicos Haematology & Oncology course. Try to answer each question before you open it — then study them properly with spaced repetition, which brings each card back just before you would forget it.
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What amino-acid change causes sickle haemoglobin, and on which chromosome is the β-globin gene?
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Valine replaces glutamic acid at position 6 of β-globin; chromosome 11.
Why? Deoxygenated HbS polymerises, turning red cells into rigid sickles that block small vessels.
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What is the first-line disease-modifying drug in sickle cell disease, and how does it help?
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Hydroxycarbamide (hydroxyurea): it increases fetal haemoglobin (HbF).
Why? HbF does not polymerise with HbS, so a higher HbF means less sickling and fewer painful crises.
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What is the first-line management of an acute sickle cell painful (vaso-occlusive) crisis?
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Analgesia within 30 minutes (a strong opioid bolus for severe pain, plus regular paracetamol and an NSAID unless contraindicated), with hydration, and oxygen if SpO2 is 95% or below.
Why? Pain is caused by microvascular occlusion and ischaemia; fluids and oxygen reduce further sickling.
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A 22-year-old with sickle cell disease has fever, chest pain, hypoxia and new bilateral infiltrates on CXR. He worsens despite oxygen, fluids, analgesia and IV antibiotics. What is the key escalation treatment?
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Exchange transfusion.
Why? This is acute chest syndrome. Exchange transfusion lowers the HbS percentage quickly without raising blood viscosity.
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What long-term infection prevention is given in sickle cell disease?
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Daily oral penicillin prophylaxis plus extra vaccines against encapsulated organisms (pneumococcal PCV20, meningococcal ACWY and B) and yearly influenza vaccine.
Why? Repeated splenic infarction causes functional asplenia (autosplenectomy), so encapsulated bacteria are dangerous.
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Which haemoglobin fraction is characteristically raised in β-thalassaemia trait?
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HbA2 (above 3.5%).
Why? With fewer β chains, spare α chains pair with δ chains to form HbA2 (α2δ2).
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Which iron chelator is given by slow subcutaneous infusion in transfusion-dependent β-thalassaemia major?
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Desferrioxamine.
Why? Every unit of blood adds iron that the body cannot excrete; chelation prevents iron overload of the heart, liver and endocrine glands.
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Which oral iron chelator needs regular blood count monitoring because it can cause agranulocytosis?
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Deferiprone.
Why? It can cause neutropenia and agranulocytosis, so neutrophil counts are checked regularly (BNF advises weekly).
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What is the gold-standard test to confirm sickle cell disease and identify the genotype (e.g. HbSS vs HbSC)?
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Haemoglobin electrophoresis (or HPLC).
Why? It separates and measures HbS, HbA, HbC, HbF and HbA2, so it distinguishes disease, trait and compound states.
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A 3-year-old with HbSS suddenly becomes pale and shocked. Hb has fallen from 80 to 40 g/L, the spleen is massively enlarged and the reticulocyte count is high. What is the diagnosis and the immediate treatment?
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Acute splenic sequestration crisis — urgent fluid resuscitation and red cell transfusion.
Why? Blood pools suddenly in the spleen, causing a rapid fall in Hb and hypovolaemia; the marrow is still working, so reticulocytes rise.
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Deletion of three α-globin genes causes ______; deletion of all four causes Hb Bart's hydrops fetalis.
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HbH disease
Why? With too few α chains, spare β chains form HbH (β4) and spare γ chains form Hb Bart's (γ4); Hb Bart's cannot release oxygen to tissues, causing death in utero.
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Deletion of three α-globin genes causes HbH disease; deletion of all four causes ______.
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Hb Bart's hydrops fetalis
Why? With too few α chains, spare β chains form HbH (β4) and spare γ chains form Hb Bart's (γ4); Hb Bart's cannot release oxygen to tissues, causing death in utero.
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Which toxicities are screened for regularly in patients on long-term desferrioxamine?
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Auditory (high-frequency hearing loss) and ocular (retinal/visual) toxicity — regular audiology and eye checks.
Why? These dose-related effects are more likely when the dose is high relative to the iron burden.