Laboratory Studies
Laboratory studies are not necessary for most people with fire ant stings; however, in severe reactions, a CBC count, coagulation studies, and a urinalysis could be obtained for the following uncommon but possible manifestations:
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Leukocytosis
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Thrombocytopenia
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Hypofibrinogenemia
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Abnormal coagulation
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Proteinuria
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Hemoglobinemia
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Hemoglobinuria
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Myoglobinemia
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Azotemia
Other Tests
Skin testing, enzyme-linked immunosorbent assay (ELISA), and radioallergosorbent testing (RAST) can be used to confirm a clinical history of fire ant hypersensitivity.
A venom ELISA assay has demonstrated equivalent sensitivity to venom RAST and is less expensive. [12] Reagents containing venom proteins are required for these tests. Because pure venom vaccines are not commercially available, whole-body extracts are used.
Patients without a clinical history of allergic reactions to fire ants should not be tested because of the high degree of asymptomatic IgE production in an exposed population.
Histologic Findings
The histologic findings depend on the stage of evolution of the lesion. In early lesions, a perivascular infiltrate of lymphocytes, neutrophils, and eosinophils is found within the dermis. Later, an intraepidermal vesicle or pustule (containing mostly neutrophils) is usually present, often with a central focus of epidermal necrosis. Dermal edema is often present. Compared with other arthropod assaults, fire ant stings are far more pustular, with more neutrophils and fewer eosinophils.
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Imported fire ant national distribution map. From http://fireant.tamu.edu. Reproduced with permission from B.M. Drees, Texas Imported Fire Ant Project Coordinator, Texas A&M University, College Station, Texas.
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Red imported fire ant worker. From http://fireant.tamu.edu. Reproduced with permission from B.M. Drees, Texas Imported Fire Ant Project Coordinator, Texas A&M University, College Station, Texas.
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Fire ant mound in lawn. From http://fireant.tamu.edu. Reproduced with permission from B.M. Drees, Texas Imported Fire Ant Project Coordinator, Texas A&M University, College Station, Texas.
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Venom sac and stinger of a fire ant. From http://fireant.tamu.edu. Reproduced with permission from B.M. Drees, Texas Imported Fire Ant Project Coordinator, Texas A&M University, College Station, Texas.
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Fire ant worker biting and stinging. From http://fireant.tamu.edu. Reproduced with permission from B.M. Drees, Texas Imported Fire Ant Project Coordinator, Texas A&M University, College Station, Texas.
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Pustules and blisters formed following fire ant stings on the arm. From http://fireant.tamu.edu. Reproduced with permission from B.M. Drees, Texas Imported Fire Ant Project Coordinator, Texas A&M University, College Station, Texas.
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Pustules and blisters formed following fire ant stings on the hand. From http://fireant.tamu.edu. Reproduced with permission from B.M. Drees, Texas Imported Fire Ant Project Coordinator, Texas A&M University, College Station, Texas.
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Fire ant bites on the foot.
