A 21-year-old man with a normal hemoglobin of 14.2 g/dL presents with a third episode of painless gross hematuria. Urinalysis shows red cells with no dysmorphism, proteinuria is absent, and renal function is normal. CT urography reveals a small area of sloughed papilla in the left kidney. His mother carries sickle cell trait. Which statement is correct?
- A Sickling cannot occur in red cells carrying HbAS, so another cause must be sought
- B Gross hematuria in sickle trait always indicates transitional cell carcinoma
- C The hypertonic acidotic renal medulla induces sickling even in HbAS red cells, causing papillary necrosis ✓
- D This picture is typical of thin basement membrane disease
Explanation
Although HbAS red cells do not sickle in systemic circulation, the renal medulla combines hypertonicity, acidity, low oxygen tension and low flow, conditions sufficient to polymerize HbS even at 40% concentration. This causes medullary microvascular occlusion, papillary necrosis, impaired concentrating ability, and painless hematuria, the classic renal manifestations of sickle trait. Most patients with sickle trait related hematuria have a benign course, so malignancy is not implied by the diagnosis itself, and thin basement membrane disease does not produce papillary sloughing on imaging.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.