What is the significance of a positive Filariasis (Antibody) IgG4 (Immunoglobulin G4) test result in a patient who has never traveled outside the United States?

From the Guidelines

A positive Filariasis AB IGG4 test in a patient who has never left the United States is likely a false positive result, and therefore, no specific treatment for filariasis is needed at this time without clinical symptoms or confirmed exposure. This test detects antibodies against filarial parasites, which are typically transmitted by mosquitoes in tropical and subtropical regions not endemic to the continental US 1. I recommend confirmatory testing with more specific assays, such as microscopy of Giemsa-stained thick and thin blood films, and consideration of alternative diagnoses. False positive results can occur due to cross-reactivity with other helminth infections or autoimmune conditions.

Key Considerations

• The patient should be evaluated for symptoms such as lymphedema, skin changes, or eosinophilia, and a detailed history should be taken to rule out any forgotten travel or exposure to potentially infected individuals.
• If the patient remains asymptomatic with no other supporting evidence of infection, monitoring without antiparasitic treatment is appropriate.
• Should symptoms develop or additional testing support a true infection, treatment with diethylcarbamazine, ivermectin, or albendazole might be considered under specialist guidance, as recommended by the Centers for Disease Control and Prevention (CDC) 1.

Diagnostic Approach

• According to the CDC, the main diagnostic test for filariasis is microscopy of Giemsa-stained thick and thin blood films, which can detect microfilariae in the blood 1.
• Serology does not differentiate between filarial species, and therefore, is not recommended as a primary diagnostic tool 1.
• The patient's test results should be interpreted in the context of their clinical presentation and exposure history, and a thorough evaluation should be conducted to rule out other potential causes of their symptoms.

From the Research

Filariasis AB IGG4 Test Results

• A patient has tested positive for Filariasis AB IGG4, but has never left the United States.
• The test results indicate the presence of IgG4 antibodies, which are a type of antibody associated with filarial infections 2.
• The presence of IgG4 antibodies can be an indicator of current or past infection with a filarial parasite, such as Wuchereria bancrofti or Brugia malayi.

Possible Explanations

• It is possible that the patient has been infected with a filarial parasite through a mosquito bite or other means, even if they have never left the United States 3.
• Alternatively, the positive test result could be a false positive, or the patient may have been exposed to a different parasite that cross-reacts with the Filariasis AB IGG4 test 4.
• The patient's medical history and travel history should be reviewed to determine the likelihood of filarial infection.

Treatment and Management

• If the patient is found to have a filarial infection, treatment with antifilarial medications such as diethylcarbamazine or albendazole may be necessary 5, 3.
• The patient should be monitored for signs and symptoms of filarial infection, such as microfilaraemia or antigenaemia, and treated accordingly 6.
• Further testing, such as PCR-based assays, may be necessary to confirm the diagnosis and monitor the patient's response to treatment 4.