Hemosiderinuria

Hemosiderinuria is the presence of hemosiderin in the urine. Hemosiderin is an insoluble storage form of iron, a protein complex that forms when iron is released from ferritin. Normally, hemosiderin is not found in the urine. Its presence indicates significant intravascular hemolysis, a condition where red blood cells are broken down within the blood vessels.

The primary cause of hemosiderinuria is prolonged or severe intravascular hemolysis. This can occur in various medical conditions such as paroxysmal nocturnal hemoglobinuria (PNH), autoimmune hemolytic anemia, mechanical heart valve hemolysis, and certain transfusion reactions. When red blood cells lyse intravascularly, hemoglobin is released. The kidney's filtration system can filter out hemoglobin, but if the rate of hemolysis exceeds the reabsorptive capacity of the renal tubules, free hemoglobin can be converted to hemosiderin within the tubular cells. These cells are then shed into the urine, leading to hemosiderinuria.

Diagnosis of hemosiderinuria is typically made by examining a urine sample using the Prussian blue stain, which stains iron deposits blue. The presence of a positive stain in the urine sediment confirms hemosiderinuria. It is an important indicator of ongoing or recent significant intravascular hemolysis and warrants further investigation to identify the underlying cause. Treatment focuses on addressing the root cause of the hemolysis.