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Performance of serologic tests used to detect heartworm infection in cats
P S Snyder1, J K Levy, M E Salute
1Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville 32610-0126, USA.
Insights
Combining heartworm antibody and antigen tests improves detection accuracy in cats. If initial antibody tests are negative but suspicion remains, further diagnostics like antigen tests or imaging are recommended.
Area of Science:
- Veterinary Medicine
- Parasitology
- Diagnostic Imaging
Background:
- Heartworm disease (Dirofilaria immitis) poses a diagnostic challenge in cats.
- Accurate detection is crucial for timely intervention and management.
Purpose of the Study:
- To compare the diagnostic performance of serum antibody (Ab) and antigen (Ag) tests against necropsy findings in shelter cats.
- To evaluate the effectiveness of combined Ab and Ag testing strategies.
Main Methods:
- A prospective study involving 330 euthanatized shelter cats.
- Blood samples collected for serum Ab and Ag testing (commercial and in-house kits).
- Comparison of serological results with post-mortem examination for Dirofilaria immitis.
Main Results:
- Adult heartworms were identified in 5.8% of cats upon necropsy.
- Combined Ab and Ag testing demonstrated higher sensitivity (100%) compared to individual tests (89.5%).
- Individual Ag and Ab tests showed higher specificity (99.4%) than combined testing (92.9%).
Conclusions:
- Combined heartworm antibody and antigen testing enhances diagnostic sensitivity in cats.
- Negative antibody tests in clinically suspicious cats warrant further investigation using antigen tests or imaging modalities like radiography or echocardiography.
Objective:
To compare heartworm serum antibody (Ab) and antigen (Ag) test results, using commercial laboratories and in-house heartworm test kits, with necropsy findings in a population of shelter cats.
Design:
Prospective study.
Animals:
330 cats at an animal shelter.
Procedure:
Between March and June 1998, 30 ml of blood was collected from the cranial and caudal venae cavae of 330 cats that were euthanatized at a local animal shelter. Results of heartworm Ab and Ag serologic tests for heartworm infection were compared with necropsy findings in this population of cats, using commercial laboratories and in-house test kits to measure serum Ab and Ag concentrations.
Results:
On necropsy, adult Dirofilaria immitis were found in 19 of 330 (5.8%) cats. Combining results from serum Ab and Ag tests achieved higher sensitivities than using serum Ab and Ag test results alone (i.e., maximum sensitivities of 100% vs 89.5%, respectively, whereas use of serum Ag and Ab test results alone achieved higher specificities compared with the use of a combination of serum Ab and Ag results (i.e., maximum specificities of 99.4% vs 92.9%, respectively).
Conclusions And Clinical Relevance:
On the basis of our findings, if a cat has clinical signs that suggest heartworm disease despite a negative heartworm serum Ab test result, an alternative heartworm Ab test, a heartworm Ag test, thoracic radiography, or two-dimensional echocardiography should be performed.