Performance of serologic tests used to detect heartworm infection in cats

Objective-To compare heartworm serum antibody (Ab) and antigen (Ag) test re sults, 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 th e cranial and caudal venae cavae of 330 cats that were euthanatized at a lo cal animal shelter. Results of heartworm Ab and Ag serologic tests for hear tworm 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 sensi tivities than using serum Ab and Ag test results alone tie, maximum sensiti vities 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 com bination of serum Ab and Ac results tie, maximum specificities of 99.4% Vs 92.9%, respectively). Conclusions and Clinical Relevance On the basis of our findings, if a cat h as clinical signs that suggest heartworm disease despite a negative heartwo rm serum Ab lest result, an alternative heartworm Aic test, a heartworm Ag test, thoracic radiography, or two-dimensional echocardiography should be p erformed.