Hemoglobinuria (hemoglobin in the urine)
Hemoglobinuria (the appearance of hemoglobin in the urine) is a sign of intravascular hemolysis of erythrocytes. With hemoglobinuria, urine is dark brown. Hemoglobinuria is preceded by hemoglobinemia.
In a healthy person, about 10% of erythrocytes are destroyed in the bloodstream, therefore, the plasma contains free hemoglobin in a concentration not exceeding 4 mg%. Free hemoglobin in blood is bound by haptoglobin. The haptoglobin-hemoglobin compound does not pass the renal filter, since its MW is 160-320 kDa. The complex enters the reticulohistiocytic system of the liver and spleen, where it undergoes cleavage to form the end products of pigment metabolism.
Hemoglobinuria occurs only when the level of free plasma hemoglobin exceeds the reserve ability of haptoglobin to bind hemoglobin. At a normal concentration of blood haptoglobin, it is 100 mg%.
The intensity of hemoglobinuria depends on the degree of hemoglobinemia, the concentration of haptoglobin in the blood, and the resorption capacity of the renal tubules.
With a low level of plasma haptoglobin, hemoglobinuria appears without significant hemoglobinemia.
Hemoglobinemia above 100-120 mg% causes increased reabsorption of hemoglobin by the cells of the renal tubules. Reabsorbed hemoglobin is oxidized in the epithelium of the proximal tubule into hemosiderin, ferritin. The cells loaded with hemosiderin are exfoliated and detected in the urine. With a large amount of hemosiderin, free-lying hemosiderin is found in the urine sediment. Hemoglobinemia over 125 mg% is accompanied by hemosiderinuria and hemoglobinuria.
Thus, laboratory signs of intravascular hemolysis are hemoglobinemia, hemoglobinuria, hemosiderinuria.
Intravascular hemolysis is typical for:
- paroxysmal nocturnal hemoglobinuria (Markiafava-Micheli disease)
- autoimmune hemolytic anemias
- post-transfusion reactions
- blood parasites (malaria)
- sickle cell hemoglobinopathy
Increased hemolysis of erythrocytes in the bloodstream is possible with:
- malignant tumors
- poisoning with snake venom, phenylhydrazine, and other chemicals