Q: Dark urine is consistent? (select one)
A) intravascular hemolysis
B) extravascular hemolysis
Dark urine is due to hemoglobinuria indicates severe intravascular hemolysis. This occurs due to overwhelming absorptive capacity of the renal tubular cells. Hemosiderin in urine confirms intravascular free hemoglobin, getting filtered by the kidneys. Also, Lactic dehydrogenase (LDH) is elevated in patients with intravascular hemolysis.
In extravascular hemolysis, spleen and liver macrophage Fc receptors bind immunoglobulin attached to RBCs and then either ingest small portions of the RBC membrane creating spherocytes or phagocytizing the RBCs.
Rother RP, Bell L, Hillmen P, Gladwin MT.
The clinical sequelae of intravascular hemolysis and extracellular plasma hemoglobin: a novel mechanism of human disease.
JAMA. 2005 Apr 6;293(13):1653-62.