Intravascular hemolysis describes hemolysis that happens mainly inside the vasculature. As a result, the contents of the red blood cell are released into the general circulation, leading to hemoglobinemia and increasing the risk of ensuing hyperbilirubinemia. Mechanism
Intravascular hemolysis is the state when the red blood cell ruptures as a result of the complex of complement autoantibodies attached (fixed) on the surfaces of RBCs attack and rupture RBCs membranes, or a parasite such as Babesia exits the cell that ruptures the RBCs membrane as it goes.Upon RBCs rupture, components of which are released and circulating in the blood plasma.These components comprise hemoglobin and others. At this stage, the hemoglobin is called free hemoglobin. Free hemoglobin (also called naked hemoglobin) is the un-bound hemoglobin that is not enclosed in the red blood cell. The naked hemoglobin is devoid of its anti-oxidant sentries that are normally available within the RBC. Free hemoglobin is thus vulnerable to be oxidized.When the serum concentration of free hemoglobin is within the physiologic range of haptoglobin, the potential deleterious effects of free hemoglobin are prevented because haptoglobin will bind to "free hemoglobin" forming a complex of "free hemoglobin-haptoglobin" evidenced by reduced amount of haptoglobin. However, during hyper-hemolytic conditions or with chronic hemolysis, haptoglobin is depleted so the remaining free hemoglobin readily distribute to tissues where it might be exposed to oxidative conditions, thus some of the ferrous heme (FeII), the oxygen-binding component of hemoglobin, of the free hemoglobin are oxidized and becoming met-hemoglobin (ferric hemoglobin).
In the end, if the plasma concentration of the "free met-hemoglobin" and/or "free hemoglobin" is still too high for proximal tubule to absorb back into the body, then hemoglobinuria occurs, indicating an extensive intravascular hemolysis. These remaining free hemoglobin entities also begin to consume nitric oxide, which is critical regulators of vascular homeostasis and basal and stress-mediated smooth muscle relaxation and vasomotor tone, endothelial adhesion molecule expression, and platelet activation and aggregation. The reduction of nitric oxide deeply disturbs the bodys mechanism to maintain the stability of the hemodynamics. Additionally, free hemoglobin manifests direct cytotoxic, inflammatory, and pro-oxidant effects that in turn negatively impact endothelial function. At the meantime, free heme exerts its multiple pro-inflammatory and pro-oxidant effects to the tissues it goes through.It is important to note that although hemosiderins are also included in the urine in the setting of intravascular hemolytic hemoglobinuria, it will be detected only several days after the onset of the extensive intravascular hemolysis and will remain detectable several days after termination of intravascular hemolysis. The phenomenon tells that the detection of hemosiderin in urine is indicative of either ongoing or recent intravascular hemolysis characterized by excessive hemoglobin and/or met-hemoglobin filtered through the renal glomerulus as well as the loss of hemosiderin-laden necrotic tubular cells. See also
Extravascular hemolysis

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