Peer-reviewed veterinary case report
How immune complex dissociation improves heartworm antigen tests
By Beall, Melissa J et al.·Published in Parasites & vectors·2017·IDEXX Laboratories, United States·View original on PubMed →
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Original publication title: Validation of immune complex dissociation methods for use with heartworm antigen tests.
- Species:
- dog
Plain-English summary
A group of dogs with unclear heartworm test results were evaluated using a special method to release heartworm antigens that might be hidden by the dog's own antibodies. Researchers found that this immune complex dissociation (ICD) method helped detect heartworm in some dogs that previously tested negative. In a study involving 12 dogs undergoing heartworm treatment, three showed a decrease in heartworm antigens after four weeks, indicating that the treatment was effective. This suggests that using ICD can help clarify heartworm diagnoses, especially in dogs that have been treated or are on preventive medication.
People also search for: dog heartworm test results · heartworm treatment for dogs · why is my dog testing negative for heartworm · heartworm antigen test accuracy
Abstract
BACKGROUND: Antigen testing is routinely used to diagnose canine Dirofilaria immitis infections. Immune complex dissociation (ICD) methods, which were employed in the original heartworm antigen tests to release antigen that was bound by endogenous canine antibodies, were discontinued with improvements in assay reagents. The purpose of this study was to evaluate different ICD methods for detection of heartworm antigen by microtiter plate ELISA and assess the performance in samples from pet dogs. METHODS: The original PetChek® Heartworm Test (IDEXX Laboratories, Inc.) utilized pepsin at an acidic pH for ICD prior to antigen testing. Performance and characteristics of the pepsin ICD method were compared with those for heat treatment (with and without EDTA) and acid treatment. RESULTS: All four methods released complexed antigen in serum samples when tested using microtiter plate ELISA. Heat treatment required ≥600 μL of serum or plasma, whereas pepsin and acid methods needed only a 50-μL sample. Samples from 1115 dogs submitted to IDEXX Laboratories between 2014 and 2016 for investigation of discrepant heartworm results were evaluated with and without pepsin ICD using the PetChek Heartworm Test. Samples from 10% (n = 112) of the dogs were antigen positive with the ICD protocol only while 90% of the results remained unchanged. In a prospective study, antigen levels with and without ICD were evaluated for 12 dogs receiving pre-adulticide heartworm treatment with a macrocyclic lactone and doxycycline for 28 days. Serial samples revealed that three dogs had a reduction in detectable heartworm antigen within 4 weeks of initiating treatment. In these cases, heartworm antigen levels could be recovered with ICD. CONCLUSIONS: Heartworm antigen testing with ICD can be a valuable diagnostic tool for patients with discrepant results that have had intermittent use of a preventive, or have been treated with a macrocyclic lactone and doxycycline. Heartworm therapies may reduce antigen production and favor immune complexing in some dogs, resulting in false-negative results. Therefore, it is important to confirm positive heartworm antigen test results before initiating therapy.
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Search related cases →Original publication on PubMed: https://pubmed.ncbi.nlm.nih.gov/29143646/