Chapter 23: Hemolytic Anemia Resulting from Infectious Agents

INTRODUCTION

• Hemolysis represents a prominent part of the overall clinical picture in many infections. Table 23–1 lists the microorganisms associated with the induction of hemolytic anemia.

MECHANISMS

• Hemolysis may be caused by:

  — Direct invasion by infecting organisms (malaria).

  — Elaboration of hemolytic toxins (Clostridium perfringens).

  — Development of autoantibodies against red blood cell antigens (Mycoplasma pneumoniae).

MALARIA

Etiology and Pathogenesis

• The world's most common cause of hemolytic anemia.

• Transmitted by bite of an infected female Anopheles mosquito.

• Parasites grow intracellularly and parasitized cells are destroyed in the spleen.

• Uninvaded cells are also destroyed (estimated at 10 × the number of infected cells).

• Erythropoietin low for degree of anemia secondary to release of inhibitory cytokines, especially in Plasmodium falciparum infection.

• Certain heterozygous mutations that interfere with invasion of red blood cells by parasites have developed in endemic areas (G-6-PD deficiency, thalassemia, other hemoglobinopathies, and hereditary elliptocytosis).

Clinical Features

• Febrile paroxysms are characteristically cyclic: Plasmodium vivax every 48 hours, Plasmodium malariae every 72 hours, and P. falciparum daily.

• Rigors, headache, abdominal pain, nausea and vomiting, and extreme fatigue accompany the fever.

• Splenomegaly typically is present in chronic infection.

• Falciparum malaria is occasionally associated with very severe hemolysis and dark, almost black urine (blackwater fever).

• Cerebral malaria may result in delirium, other neurologic manifestations.

• Organ dysfunction (respiratory insufficiency and renal failure) may be present.

Laboratory Features

• Signs of hemolytic anemia.

• Thrombocytopenia nearly always present.

• Diagnosis depends on demonstration of the parasites on the blood film (Fig. 23–1) or the appropriate DNA sequences in the blood.

• If greater than 5 percent of red cells parasitized or if two ring forms in a red cell, P. falciparum infection usually present.