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in Journal of the American Veterinary Medical Association

Summary

Results of commercially available diagnostic test kits and commercial laboratory test results were compared for ability to detect FeLV antigen. Results of the immunofluorescent antibody (ifa) test were compared with test kit elisa results and with results of a system in which samples were applied to an absorbent material, dried, sent to a laboratory, eluted, and assayed by a plate elisa. Test kits were generally highly sensitive and specific, compared with the ifa test performed at a commercial laboratory. Feline heterophile antibody, specific for mouse immunoglobulin, was detected in approximately 0.14 to 0.57% of the cat population. Test kits B, E, and D contain reagents that correct for antimouse antibodies. During 1989 and 1990, 2,229 feline serum samples were tested for FeLV antigen (gsa p27); positive elisa results were obtained for 204 (9%) of the samples. Results for 32 (1.4%) samples were interpreted as equivocal (color development slightly exceeded that of the negative control, but was much less than that of the positive control). Collectively, the data indicate that when testing serum or saliva, a negative test result may be a good predictor that a cat is not infected. In populations of cats in which FeLV prevalence is low, a positive test result may not be reliable and thus, a confirmatory test should be performed.

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in Journal of the American Veterinary Medical Association

Summary

Feline sera were submitted to the Cornell Feline Health Center (n = 497) or to the New York State Diagnostic Laboratory (n = 1,565) for feline immunodeficiency virus (fiv) testing. Some sera (n = 166) were submitted for confirmation of previous fiv-positive results; 151 of these sera had been tested at the referring veterinary practice or laboratory, using an in-house elisa. Excluding the samples submitted for confirmation, a total of 173 samples (9.1%) were fiv-positive; 11.6% of the clinically ill or high-risk cats and 0.49% of the healthy, low risk cats were positive for fiv antibody.

A commercially available elisa for detection of antibody to fiv was evaluated in relation to the immunofluorescent antibody (ifa) test and the immunoblot assay. The elisa was interpreted according to the manufacturer's instructions, with the ratio of sample optical density to positive control optical density (s/p) determining a positive or negative result. The elisa results based on the s/p interpretation were compared with a kinetics-based (kela) interpretation of the elisa. The kela values were reported as positive, negative, or equivocal.

Using the immunoblot as the standard, elisa (s/p interpretation) had sensitivity of 0.93 and specificity of 0.98, whereas the ifa test had sensitivity of 0.95 and specificity of 0.98. However, the sensitivity and specificity of the elisa (s/p interpretation) were markedly reduced for sample results falling in the kela equivocal range, indicating that equivocal results were valid interpretations for some sera.

A high number (22.5%) of the samples submitted for confirmation of a positive result from use of the in-house elisa were determined to be negative for fiv antibody. Operator error or incorrect interpretation of the in-house elisa were thought to be the cause of most of these false-positive test results.

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To evaluate sensitivity and specificity of a new ELISA for antibodies against Mycobacterium avium subsp paratuberculosis.

Design—Cross-sectional observational survey.

Sample Population—Serum samples from 590 cattle that were infected with M avium subsp paratuberculosis and 723 cattle that were not infected.

Procedure—Serum samples were tested by use of an ELISA for antibodies against M avium subsp paratuberculosis.

Results—Sensitivity of the test varied from 15.4 to 88.1%, depending on the clinical stage and bacterial shedding status of the cattle.

Conclusions and Clinical Relevance—Results obtained with use of the new ELISA agreed favorably with those of a previous ELISA. Practitioners must be aware of variability in the sensitivity of the test, which depends on the clinical and shedding status of the cattle, because this may affect interpretation of test results. (J Am Vet Med Assoc 2001;218:1163–1166)

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in Journal of the American Veterinary Medical Association