Pathology > Basic Hematology > Red Cell Disorders > Miscellaneous

Miscellaneous

Infections may initiate a hemolytic crisis especially in patients with G-6-PD deficiency. In people with meningcoccal or pneumococcal septicemia the infection may result in a microangiopathic hemolytic anemia. Clostridial endotoxin may also cause hemolysis.

Intravascular and extravascular hemolysis of infected RBCs may occur in malaria.

Other causes of hemolysis include hypersplenism, hypophosphatemia, and certain snake venoms.

In Plasmodium falciparum the young trophozoites seen above will develop into schizonts, lysing the RBCs, and initiating another cycle of infection about every 48 hours.

Erythrocytes are protected from complement attack by the complement (C3) inactivating proteins: decay-acclerating factor (DAF), C8- binding protein (C8-bp), and membrane inhibitor of reactive lysis (MIRL). Each of these proteins are variably deficient in people with paroxysmal nocturnal hemoglobinuria (PNH).

PNH is a clonal disorder with an abnormality in the gene involved in the synthesis of the glycosyl-phosphatidylinositol (GPI) anchor in the RBC membrane.

 

DAF and MIRL are missing from the RBC membrane in PNH because the abnormal GPI cannot anchor the proteins.

Any protein requiring the GPI anchor to attach to the RBC membrane will be unable to hold on and therefore missing or deficient. This explains the absence of DAF, C8-bp, MIRL, acetyl cholinesterase, leukocyte alkaline phosphatase, the Fc receptor, and others in PNH.

 

DAF and MIRL are missing from the RBC membrane in PNH because the abnormal GPI cannot anchor the proteins.

Hemoglobinuria, often on awakening, is a characteristic symptom of PNH, but one not always present. This is of course secondary to chronic intravascular hemolysis.

Iron deficiency secondary to chronic loss of iron in the urine is common.

The peripheral blood shows a mild to moderate macrocytosis and if Fe deficient, microcytosis and hypochromia.

The WBC and platelet count are usually decreased due to complement mediated destruction, as both lack DAF.

Bone marrow erythroid hyperplasia is common, but hypoplasia and pancytopenia may be seen.

The lack of DAF, MIRL etc. allows C3 to bind activating the alternate pathway resulting in lysis by C5-9.

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