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) are destroyed, thereby releasing free hemoglobin into the plasma. Hemoglobin (Hb) in urine: Between 135 and 175 grams/liter for men. Between 120 and 155 grams/liter for women.