Hemosiderinuria (syn. haemosiderinuria) is the presence of hemosiderin in urine. It is often the result of chronic intravascular

hemolysis Hemolysis or haemolysis (), also known by several other names, is the rupturing (lysis) of red blood cells (erythrocytes) and the release of their contents (cytoplasm) into surrounding fluid (e.g. blood plasma). Hemolysis may occur in vivo o ...

, in which hemoglobin is released from red blood cells into the bloodstream in excess of the binding capacity of

haptoglobin Haptoglobin (abbreviated as Hp) is the protein that in humans is encoded by the ''HP'' gene. In blood plasma, haptoglobin binds with high affinity to ''free'' hemoglobin released from erythrocytes, and thereby inhibits its deleterious oxidative ...

. The function of haptoglobin is to bind to circulating hemoglobin, thereby reducing renal excretion of hemoglobin and preventing injury to kidney tubules. The excess hemoglobin that is not bound to haptoglobin is filtered by the kidneys and reabsorbed in the

proximal convoluted tubule The proximal tubule is the segment of the nephron in kidneys which begins from the renal pole of the Bowman's capsule to the beginning of loop of Henle. It can be further classified into the proximal convoluted tubule (PCT) and the proximal straig ...

, where the iron portion is removed and stored in

ferritin Ferritin is a universal intracellular protein that stores iron and releases it in a controlled fashion. The protein is produced by almost all living organisms, including archaea, bacteria, algae, higher plants, and animals. It is the primary ' ...

hemosiderin Hemosiderin image of a kidney viewed under a microscope. The brown areas represent hemosiderin Hemosiderin or haemosiderin is an iron-storage complex that is composed of partially digested ferritin and lysosomes. The breakdown of heme gives rise ...

. The tubule cells of the proximal tubule become damaged, slough off with the hemosiderin and are excreted into the urine, producing a "brownish" color. It is usually seen three to four days after the onset of hemolytic conditions.

Hemoglobinuria Hemoglobinuria is a condition in which the oxygen transport protein hemoglobin is found in abnormally high concentrations in the urine. The condition is caused by excessive intravascular hemolysis, in which large numbers of red blood cells (RBCs) ...

is another indicator of intravascular hemolysis, but disappears more quickly than hemosiderin, which can remain in the urine for several weeks; therefore, hemosiderinuria is a better marker for intravascular hemolysis.

References

Red blood cell disorders {{med-sign-stub