Medical Emergencies · patient case question
Which change to the sickled erythrocyte contributes most directly to the anaemia and to vaso-occlusive crisis?
Patient case: A painful crisis in a young adult
demo: 24-year-old male
chief: Severe generalised bone pain, worst in the mandible and long bones, for two days.
history: Sickle cell anaemia diagnosed in infancy. Two hospital admissions in the past year for painful crises. He became dehydrated at a football match the day before this episode began.
meds: Hydroxyurea, folic acid.
findings: Afebrile, tachycardic. Panoramic radiograph shows a stepladder trabecular pattern with enlarged marrow spaces and generalised radiolucency of the jaws.
Show answer and explanation
Correct answer: A. A markedly shortened red cell lifespan
- A. Correct. Polymerised haemoglobin S distorts the cell into a rigid sickle. Those cells are cleared by the spleen and haemolyse in the circulation, cutting the normal 120-day lifespan to roughly 10 to 20 days. The rigid cells also jam in the microvasculature, which is the vaso-occlusion that causes the pain.
- B. Haemoglobin S has reduced oxygen affinity, shifting the dissociation curve to the right. In any case increased affinity would not drive the sickling process; deoxygenation does.
- C. Sickled cells are less deformable, not more. Loss of the flexibility that lets a normal biconcave disc squeeze through a capillary is precisely why they occlude vessels.
- D. The opposite is true. Any process that lengthened red cell survival would improve, not worsen, the anaemia.
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