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Screening tests for FeLV and FIV

Levy J, Crawford PC, Tucker SJ. Performance of 4 Point-of-Care Screening Tests for Feline Leukemia Virus and Feline Immunodeficiency Virus. J Vet Intern Med.  2017;31:521–526.

Identification of cats infected with Feline Leukemia Virus (FeLV) or Feline Immunodeficiency Virus (FIV) is critical to controlling these potentially lethal agents of disease. To this end, point of care ELISA kits are often used for screening for infection. As the authors state,” life or death decisions based on a single test result make the use of point-of-care screening tests a high-stakes event.” This investigation compared the performance of four such kits: SNAP® Combo FeLV Ag/FIV Ab Test3 (bidirectional flow ELISA), WITNESS® FeLV-FIV Test Kit4 (lateral flow immunochromatography with colloidal gold), Anigen® Rapid FIV Ab/FeLV Ag Test Kit5 (lateral flow immunochromatography with colloidal gold), and VetScan® Feline FeLV/FIV Rapid Test6 (lateral flow immunochromatography with colloidal gold).

146 FeLV+, 154 FeLV−, 94 FIV+, and 97 FIV− samples were tested using these kits.

Sensitivity and specificity, respectively, for FeLV were SNAP® (100%/100%), WITNESS®(89.0%/95.5%), Anigen® (91.8%/95.5%), and VetScan® (85.6%/85.7%).

Sensitivity and specificity for FIV were SNAP® (97.9%/99.0%), WITNESS® (94.7%/100%), Anigen® (96.8%/99.0%), and VetScan®(91.5%/99.0%).

The SNAP® test had the best performance for FeLV, but there were no significant differences for FIV. In typical cat populations with seroprevalence of 1–5%, a majority of positive results reported by most point-of-care test devices would be false-positives. This could result in unnecessary segregation or even euthanasia. As the authors state: “Positive test results, especially for cats in low-risk categories, should be confirmed with alternative testing modalities, such as a different type of point-of-care test, PCR, or, in the case of FeLV, IFA. However, all available diagnostic tests for FeLV and FIV have some intrinsic level of inaccuracy, making it difficult to resolve discordant results between screening and confirmatory tests with certainty.” (MK)

See also:
Westman ME, Malik R, et al. Duration of antibody response following vaccination against feline immunodeficiency virus. J Feline Med Surg.2016 Oct 21. pii: 1098612X16673292. [Epub ahead of print]