From the Guidelines
The Quest Diagnostics FILARIA AB IGG4 test can cross-react with several non-filarial infections, including strongyloidiasis, ascariasis, schistosomiasis, echinococcosis, toxoplasmosis, and trypanosomiasis, as well as non-parasitic conditions such as hypergammaglobulinemia and certain autoimmune disorders. These cross-reactions occur due to molecular mimicry, where many helminths share conserved protein structures that can trigger similar immune responses 1. When interpreting positive FILARIA AB IGG4 results, clinicians should consider the patient's travel history, clinical presentation, and results of other diagnostic tests to differentiate between true filarial infection and cross-reactivity from these other conditions 1. Some key points to consider in the laboratory diagnosis of blood and tissue parasites include:
- Microscopy is the cornerstone of laboratory identification but is highly subjective and dependent on technologist experience and training
- Proper specimen collection and transport are essential components of morphology and culture-based techniques
- Serology shows significant cross-reactivity among helminths, including filaria
- There are a limited number of antigen detection methods available for blood and tissue parasites in the United States
- Automated hematology analyzers may fail to detect malaria or babesiosis parasites; request manual stain and evaluation if either agent is suspected
- NAATs are useful for detection of low parasitemia or in specifically identifying organisms that cannot be differentiated microscopically
- Antigen and nucleic acid detection methods should not be used to monitor response to therapy, since antigen or DNA may be detectable for days to weeks after successful treatment
- NAATs for detecting blood and tissue parasites are currently available only from specialized laboratories and turnaround time may be prolonged 1. In endemic areas where multiple parasitic infections may coexist, additional confirmatory testing may be necessary to accurately diagnose the infection. The following infections can cross-react with the Quest Diagnostics FILARIA AB IGG4 lab test:
- Strongyloidiasis
- Ascariasis
- Schistosomiasis
- Echinococcosis
- Toxoplasmosis
- Trypanosomiasis
- Hypergammaglobulinemia
- Certain autoimmune disorders It is essential to consider these potential cross-reactions when interpreting positive FILARIA AB IGG4 results to ensure accurate diagnosis and treatment of the underlying infection 1.
From the Research
Infections that can Cross-React with Quest Diagnostics FILARIA AB IGG4 Lab Test
- Strongyloidiasis: Studies have shown that there is a positive correlation between the titres of antifilarial IgG4 and the optical densities of anti-Strongyloides IgG4-ELISA 2.
- Lymphatic filariasis: This is the primary infection that the Quest Diagnostics FILARIA AB IGG4 lab test is designed to detect, with IgG4 antibodies being highly elevated in patients with filariasis 3, 4.
- Loa loa infection: While IgG4 antibodies to the recombinant antigen Ll-SXP-1 are highly specific for Loa loa infection, there may be some cross-reactivity with other filarial infections 5.
- Other helminthiases: There may be some cross-reactivity between the Quest Diagnostics FILARIA AB IGG4 lab test and other helminthiases, such as onchocerciasis and mansonellosis, although the specificity of the test for filariasis is generally high 5.
Factors Influencing Cross-Reactivity
- The presence of common antigenic determinants: Cross-reactivity among different infections can occur due to the presence of common antigenic determinants, which can lead to the production of antibodies that react with multiple infections 6.
- Immunologic mechanisms: Cross-reactivity can be mediated by immunologic mechanisms, such as the production of IgG4 antibodies, which can recognize multiple infections 2, 4.