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Detecting hemosiderinuria, secondary to excess hemolysis, as in incompatible blood transfusions, severe acute hemolytic anemia, or hemochromatosis
When the plasma hemoglobin level is >50 to 200 mg/dL after hemolysis, the capacity of haptoglobin to bind hemoglobin is exceeded, and hemoglobin readily passes through the glomeruli of the kidney. Part of the hemoglobin is absorbed by the proximal tubular cells where the hemoglobin iron is converted to hemosiderin. When these tubular cells are later shed into the urine, hemosiderinuria results. If all of the hemoglobin cannot be absorbed into the tubular cells, hemoglobinuria results.
Hemosiderin is found as yellow-brown granules that are free or in epithelial cells and occasionally in casts in an acidic or neutral urine.
Hemosiderin: negative (reported as positive or negative)
Hemoglobin (internal specimens only): negative
RBC (internal specimens only): 0-2 rbc/hpf
A positive hemosiderin indicates excess red cell destruction.
Hemosiderinuria may still be detected after hemoglobin has cleared from the urine and hemoglobin dipstick is negative.
No significant cautionary statements
Henry JB: Clinical Diagnosis and Management by Laboratory Methods. 18th edition. Philadelphia, WB Saunders Company, 1991, pp 412-413