Haemosiderin (urinary)

Haemoglobinuria and haemoglobinaemia occur when haemoglobin is released into the plasma in greater amounts than can be bound to haptoglobins. Haemoglobin bound to haptoglobin is unable to cross the glomerular membrane, but free haemoglobin is sufficiently small to be excreted in the urine. In acute intravascular haemolysis, haemoglobin appears in the urine more or less intact. In chronic haemoglobinuria, some of the pigment is taken up by the kidney and degraded and haemosiderin granules are passed into the urine. The presence of haemosiderin in the urine indicates the recent or chronic release of free haemoglobin into the circulating plasma, and the depletion of haemopexin and haptoglobin. Haemosiderin is usually attributable to intravascular haemolysis, but may originate from conditions such as haemorrhagic pancreatitis, in which breakdown of blood cells occurs in the peritoneal cavity.

Urinary haemosiderin may aid diagnosis of haemolytic anaemia associated with intravascular haemolysis, eg. haemolytic transfusion reactions, cold haemagglutinin disease, paroxysmal nocturnal haemoglobinuria (PNH), thalassaemia major, sickle cell disease, trauma due to replacement mechanical heart valves, and drug-induced oxidative stress (with/without G6PD/ PK deficiency) Diagnosis and assessment of iron overload conditions eg. post-transfusion, hereditary haemochromatosis, etc.