MBBS viva · Haematology
Sickle cell disease — blood film, crises and management viva
A final-prof viva on interpreting a sickle-cell blood film, defining the genotype, framing the crisis types, and justifying hydroxyurea, transfusion and gene therapy. Examiner expects mechanism, trial-level evidence and structured crisis management, not labels.
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NEET-PGINICETUSMLEPLAB
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Interpretation
The examiner presents a peripheral blood film showing elongated crescent-shaped sickled cells, target cells, boat-shaped cells and Howell-Jolly bodies, and asks: "What do you see, what is the underlying disease, and how would you confirm and manage it?"
- Film findings: sickled cells (pathognomonic), target cells, polychromasia (reticulocytosis) and Howell-Jolly bodies (indicating functional asplenia / autosplenectomy). These together point to sickle cell disease with chronic haemolysis and absent splenic function.[1]
- Confirm the genotype with haemoglobin electrophoresis or HPLC — HbSS shows HbS with no HbA; HbSC shows HbS and HbC; HbS-beta-thalassaemia shows HbS with reduced/absent HbA and a raised HbA2. The sickling test (Sickledex) confirms the presence of HbS but does not distinguish trait from disease.[2]
- Pathophysiology in one sentence: a single glutamic-acid-to-valine substitution at position 6 of beta-globin (Glu6Val) lets HbS polymerise under deoxygenation, producing rigid sickled cells that cause vaso-occlusion, haemolysis and endothelial damage.
Key points
The examiner will probe each of these; be ready to defend them at viva depth:
- Genetics — autosomal recessive, chromosome 11; HbSS (severe), HbSC (moderate), HbS-beta-thal. Sickle cell trait (HbAS) protects against severe falciparum malaria — balanced polymorphism explaining the geographic distribution.[2]
- The four crisis types — vaso-occlusive (commonest, painful bones/chest/abdomen), splenic sequestration (child, sudden splenomegaly and anaemia — emergency transfusion), aplastic (parvovirus B19, sudden Hb drop with low reticulocytes, self-limiting), hyperhaemolytic (raised reticulocytes, haemolysis).[1]
- Acute chest syndrome = leading cause of death — new infiltrate + hypoxia in a sickle cell patient; manage with oxygen, antibiotics (cephalosporin + macrolide), transfusion/exchange transfusion, and incentive spirometry.[1]
- Crisis bundle — oxygen, IV hydration (isotonic, avoid overload), titrated IV morphine (never under-treat pain), treat the trigger (infection, dehydration); incentive spirometry to prevent ACS.
- Hydroxyurea (hydroxycarbamide) — raises HbF, reduces crises ~50 percent and mortality (MSH trial); for nearly all from 9 months.[1]
- Stroke prevention — annual transcranial Doppler from age 1-2; chronic transfusion if abnormal prevents ~90 percent of strokes (STOP trial); acute stroke = emergency exchange transfusion to HbS under 30 percent.
- Functional asplenia by age 5 — encapsulated organisms (S. pneumoniae, Hib, N. meningitidis); vaccinate, penicillin V prophylaxis to 5, any fever = urgent empirical IV antibiotics.
- Curative therapy — haematopoietic stem cell transplant (matched sibling) and gene therapy exagamglogene autotemcel (exa-cel, CRISPR-Cas9), approved 2023-2024.[1]
References
- Kato GJ, et al. Sickle cell disease. Nat Rev Dis Primers 2022.[1]
- Rees DC, et al. Sickle-cell disease. Lancet 2010.[2]
References2ShowHide
- [1]Kato GJ, Piel FB, Reid CD, et al. Sickle cell disease. Nature Reviews Disease Primers, 2018.PMID 29542687
- [2]Rees DC, Williams TN, Gladwin MT. Sickle-cell disease. Lancet, 2010.PMID 21131035