Physiology

• Mechanism: with intravascular hemolysis, hemoglobin is released from hemolyzed RBC’s into the blood, exceeding the binding capacity of haptoglobin -> excess hemoglobin is filtered by the kidney
  • Some of this hemoglobin is excreted in the urine, resulting in hemoglobinuria (with “coca cola-colored” urine)
  • Some of this hemoglobin is reabsorbed in the proximal convoluted tubule, where the iron portion is removed and stored in ferritin or hemosiderin -> proximal tubule cells slough off (containing the hemosiderin) and are excreted into the urine, resulting in hemosiderinuria
    • Urine hemosiderin (composed of a complex of ferritin, denatured ferritin, and other material) can be detected in iron-stained urinary sediment (within the sloughed proximal tubular cells)
• Diagnostic Utility
  • Urine hemoglobin disappears more quickly from the urine than hemosiderin, making it less sensitive for the presence of hemolysis (especially in cases with intermittent hemolysis)
  • Urine Hemosiderin can remain in the urine for several weeks (making it a more sensitive marker for hemolysis in the recent past): however, after an acute episode of intravascular hemolysis, several days may pass before urinary hemosiderin can be detected

Etiology

• Hemolytic Anemia (see Hemolytic Anemia, [[Hemolytic Anemia]]):

References

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