Prospective determination of the specificity of a commercial snake venom detection kit in urine samples from dogs and cats

Abstract

Objective To determine the specificity of a snake venom detection kit in urine samples from dogs and cats presenting to a referral centre for diseases unrelated to snake envenomation.Design Urine was collected from 50 dog and 25 cats presented for investigation and treatment of diseases unrelated to snake envenomation. Urine was collected as a voided sample, by cystocentesis or by catheterisation, and routine urinanalysis was performed. Snake venom testing was performed within 2 h of collection using a commercially available snake venom detection kit, which was observed continuously during the 10-min colour reaction phase for evidence of a visible colour indicating a positive test. ResultsNo false-positive reactions occurred in any sample analysed. ConclusionThe snake venom detection kit appears to have 100% specificity for using urine as a test sample. T he CSL Snake Venom Detection Kit® is a rapid, freeze-dried, sandwich enzyme immunoassay. Each well of the test kit contains pairs of antibodies against a particular snake immunotype. Tiger, brown, black, death adder and taipan snake immunotypes are represented in the kit, together with a negative control, positive control and a blank well. One of the antibodies is attached to the plastic surface of the well and the other is modified by attachment of peroxidase and left free within the well. Any venom present in the test sample binds to the antibodies in the well and a washing phase subsequently removes any unbound material. Tetramethylbenzidine chromogen and peroxide are added to the wells, with oxidation of tetramethylbenzidine resulting in the development of a blue colour considered positive for a specific venom immunotype. This allows administration of the appropriate monovalent antivenom to the affected patient if indicated.1 Clinical sensitivity and specificity based on the presence of symptoms have been reported in the human literature at 53% and 83%, respectively.2 Cross-reactivity to other snake venoms and anecdotal incidences of false positives in urine containing haemoglobin have also been described.3-5 A case of brown snake bite without definitive evidence of envenomation, but displaying a positive result for black snake envenomation on snake venom detection kit testing of urine, has also been reported. 6 The incidence of false positives for urine samples is currently unknown in the veterinary population. Materials and methodsCats and dogs presenting to Murdoch University Veterinary Hospital for conditions other than suspected snake envenomation were assessed routinely and any urine samples obtained during the study period (March 2008 to August 2009) with sufficient residual volume were used for this study. On completion of the study, the medical records of the patients were reviewed to confirm that the patient's disease process had been unrelated to snake envenomation. This project had full Murdoch University Animal Ethics Committee approval.All urine samples had the method of collection recorded and were stored at room temperature after collection....

Venomous and Poisonous Australian Animals of Veterinary Importance: A Rich Source of Novel Therapeutics

“…Although bite site swabs can be used, bite sites are rarely identified in animals either in life or during a postmortem examination. False positives with SVDKs have been anecdotally reported; however, a study on urine from 50 dogs and 25 cats presenting to veterinary clinics demonstrated no false positive reactions, so test specificity was estimated at 100% on urine as a test sample [19]. False negatives can occur with high venom concentration saturating binding antibodies in the kit (known as the “hook effect”), with venom levels below the limit of detection in subclinical envenomation, and insufficient time for venom to concentrate in the urine, or an extended period of time between envenomation and testing, which results in venom levels in urine below the level of detection [19].…”

IN THIS ISSUE – June 2010

“…The snake venom detection kit used in this study had no false positive results using dog and cat urine as a test sample, although the authors stress that a negative result should not be taken as proof that envenomation has not occurred 4 …”

“…The snake venom detection kit used in this study had no false positive results using dog and cat urine as a test sample, although the authors stress that a negative result should not be taken as proof that envenomation has not occurred. 4 False-positive results have been reported for urine samples in snake envenomation kits in human medicine, but it is not know if false positives are produced in the veterinary setting.…”

Red‐bellied black snake (Pseudechis porphyriacus) envenomation in 17 dogs: clinical signs, coagulation changes, haematological abnormalities, venom antigen levels and outcomes following treatment with a tiger‐brown snake antivenom

“…The SVDK has been shown to be highly specific for detecting snake venom in urine. 16 Patients were treated with an experimental antivenom that has since become a licensed veterinary medicine for use in Australia: tigerbrown snake antivenom 8000 units (TBAV; Padula Serums Pty Ltd, VIC, Australia. APVMA Approval No.…”