Laboratory Findings

Laboratory findings of hemolytic anemia consist of:

1. Reduced red cell survival and evidence of accelerated hemoglobin catabolism

2. Evidence of increased erythropoiesis.

Accelerated Hemoglobin Catabolism

Accelerated hemoglobin catabolism varies with the type of hemolysis as follows:

• Extravascular hemoglobin catabolism (see Figure 7-1)

• Intravascular hemoglobin catabolism (see Figure 7-2).

Hemoglobin Catabolism Pathway
Fig. 7-1. Extravascular hemoglobin catabolism following extravascular destruction of the RBC.
Intravascular disruption of red blood cell (RBC) membrane and release of hemoglobin in circulating blood

Hemoglobin-Haptoglobin o

Haptoglobin Hemopexin-Heme ^-

Free Hemoglobin t

Heme

Hemopexin

^ Albumin Methemalbumin

Methemoglobin

Urobilinogen Pathway

Liver (Hepatocyte)

Liver (Hepatocyte)

Hemoglobinuria Urobilinogen

Hemoglobinuria Urobilinogen

Oxyhemoglobin Methemoglobin

Fig. 7-2. Intravascular hemoglobin catabolism following intravascular hemolysis. Hemoglobin-haptoglobin, hemopexin-heme, and methemalbumin are cleared by hepatocytes. Heme is converted to iron and bilirubin. The common pathway for both extravascular and intravascular hemolysis is the conjugation of bilirubin (bilirubin glucuronide) by the hepatocytes, its excretion in bile, and ultimately formation of the urobilinogen by the bacteria in the gut. Part of urobilinogen enters in enterohepatic circulation and part is excreted by the kidney in urine, and the remainder of urobilinogen is excreted in stool (see Fig. 7-1).

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