COMPARISON OF 8 DIAGNOSTIC BLOOD-TESTS FOR HEARTWORM INFECTION IN DOGS

Sixty-one adult dogs not on heartworm (Dirofilaria immitis) preventive were included in this study. Blood tests performed for D. immitis inf ection were modified Knott's microfilaria, fluorescent immunoassay (FI AX) antibody, and six antigen tests: DiroCHEK(R) (Synbiotics, Inc., Sa n Diego, CA), PetChek(R) (IDEXX Laboratories, Inc., Westbrook, ME), As sure/CH(TM) (Synbiotics, Inc.), Snap(TM) (IDEXX Laboratories, Inc.), U NI-TEC(R) CHW (Synbiotics, Inc.), and CITE(R) Semi-Quant(TM) (IDEXX La boratories, Inc.). At necropsy, 33 dogs (54%) were infected with D. im mitis, 27 (82%) had patent and six (18%) had occult infections. DiroCH EK was the most sensitive test and Snap was the least sensitive test i n this study. Assure/CH and FIAX were the only tests with a specificit y and predictive value for a positive test < 100%. Predictive value of a negative antigen test was highest for DiroCHEK, and lowest for Snap and CITE Semi-Quant. DiroCHEK was the most accurate antigen test, and correctly identified more study dogs as infected or not than UNI-TEC CHW, CITE Semi-Quant, and Snap. All six antigen tests were semi-quanti tative and distinguished between dogs with less than or equal to five total heartworms and dogs with > 20 at necropsy. Assure/CH distinguish ed between dogs with less than or equal to five total heartworms and t hose with greater than or equal to six (P < 0.05). Most incorrect or f alse negative test results occurred in dogs with less than or equal to five heartworms.