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DIAGNOSIS OF CANINE HEARTWORM INFECTION | No. of Samples Sample Source 51 9 1 6 10 37 Table 1. Overview of Samples Used in This Study Sample Type CHW screening clinic (low risk)* Annual CHW screening (low risk)* Laboratory (uninfected)§ Laboratory (uninfected)§ Laboratory (experimental infection)§ Laboratory (experimental infection)§ Whole blood Plasma Whole blood Serum/plasma Whole blood Serum/plasma Classification Negative Negative Negative Negative Positive Positive * Samples were collected from dogs participating in CHW screening or outpatient clinics at the College of Veterinary Medicine, Western University of Health Sciences. These animals were pets of veterinary faculty, staff, and students living in an area of Southern California with low prevalence of CHW infection. Most dogs (38/51 whole blood samples), including all dogs with his- tory of living or travelling outside of California, were on a monthly CHW preventive program. § Samples were obtained from a commercial laboratory. These samples were collected from dogs that had been experimentally infected by IV transplantation with adult heartworms 4.5 to 12 months before sampling or inoculation of L3 larvae 1 to 3 years before sampling. Uninfected control dogs were also sampled. ÌiÃÌÃÊ>ÀiÊ«iÀvoÀmin}°Ê nÊÌhiÊ«>ÃÌÊ£äÊÞi>ÀÃ]ÊÃomiÊÌiÃÌÃÊh>ÛiÊ been reformulated and new tests have been introduced. We evaluated the performance of 4 immunoassays cur- rently available for point-of-care diagnosis of CHW infec- tion. Samples from a total of 114 dogs were tested, including 51 negative and 10 positive ethylenediaminetetraacetic acid / ®ÊÜholiÊLloo`ÊÃ>m«liÃ]Ê>n`Ê£xÊni}>ÌiÛiÊ>n`ÊÎÇÊ«oÃi- tive serum or plasma samples (Table 1). Test Results /iÃÌÃÊÜiÀiÊ`iÃi}n>Ìi`Ê ]Ê ]Ê ]ÊoÀÊ °Ê onVoÀ`>nViÊ>mon}Ê the tests was excellent. UÊ/hiÊonlÞÊ`iÃVoÀ`>nÌÊÌiÃÌÊÜ>ÃÊ>ÊÜi>kÊ«oÃiÌiÛiÊonÊ/iÃÌÊ Ê that was negative on all other tests. The sample, which Ü>ÃÊÜholiÊLloo`ÊvÀomÊ>Êhi>lÌhÞ]ÊloÜ-ÀiÃkÊ`o}]ÊÜ>ÃÊÀiÀÕnÊ on all tests with the same results using both whole blood and plasma. UÊ oniÊovÊ ÌhiÊ££{ÊÃ>m«liÃÊÀÕnÊonÊ/iÃÌÃÊ ]Ê ]Ê>n`Ê ÊÜiÀiÊ inÛ>li`ÆÊÓÊÃ>m«liÃÊÀÕnÊonÊ/iÃÌÊ control line and were declared invalid. The same samples were repeated successfully on additional Test B units. The ability of the CHW tests to correctly identify CHW diseased dogs (sensitivity) and CHW disease-free dogs (specificity) was determined using the described criteria for identification of diseased and nondiseased samples (Table 2). /iÃÌÃÊ ]Ê ]Ê>n`Ê Êi>VhÊ`imonÃÌÀ>Ìi`Ê£ää¯Ê sensitivity and 100% specificity, while Test A demonstrated 100% sensitivity and 98.5% specificity. Test A # C D Test Name (Type; Manufacturer) Table 2. Sensitivity & Specificity of CHW Tests Sensitivity VetScan Canine Heartworm Rapid Test (ICT; abaxis.com) Solo Step CH (ICT; heska.com) Canine Heartworm Test (ICT; safepath.com) SNAP Canine Heartworm Antigen Test Kit (ELISA; idexx.com) (No. positive/No. diseased) 100% (47/47) 100% (47/47) 100% (47/47) 100% (47/47) ELISA = enzyme-linked immunosorbent assay; ICT = immunochromatographic test All assays were run and scored by a single evaluator (Barr) according to the manufacturer’s directions for use. The evaluator was blinded to status of serum and plasma samples, but only partially blinded to status of whole blood samples due to awareness that most of these samples came from a low-risk population. July/August 2011 Today’s Veterinary Practice 35 Ê`i`ÊnoÌÊ`iÛilo«Ê>Ê«oÃiÌiÛiÊ Specificity (No. negative/No. disease- free) 98.5% (66/67) 100% (67/67) 100% (67/67) 100% (67/67)