Figure 4.5 Extravascular hemolysis: increased bilirubin and decreased haptoglobin.
Under conditions of extravascular lysis, these conditions are present:
• Hemoglobin, hematocrit, and red cell count are low.
• Serum bilirubin is elevated.
• Reticulocyte count is elevated.
• Hepatosplenomegaly may be seen.
The Physiology of Hemolysis
Distinguishing between intravascular and extravascular hemolysis can be accomplished by paying careful atten-
tion to laboratory data. Yet, it is imperative for a student to understand why each of these events is taking place. When considering intravascular lysis, conditions that may predispose to rapid and volatile lysis within vessels may activate complement, an efficient accessory to the hemolytic process. Red blood cells burst, releasing their contents, and the alpha and beta dimers of hemoglobin are released immediately into the plasma. From the plasma they are bound to haptoglobin. The hemoglo-bin-haptoglobin complex is too large to be filtered by the kidneys, so it is not excreted but rather transported to the liver, where it is destroyed and broken down. The actual haptoglobin measurement of the plasma is lower in a hemolytic event, indicating that there are no sites
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