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4: Use of the CSL Venom Detection Kit

Venom Detection Kits are frequently used in patients attending emergency departments but there is a need for caution in interpreting their results.

Venom Detection Kits should not be used in isolation to diagnose or exclude envenomation.

A negative result of a Venom Detection Kit test should not be used to exclude envenomation. In our study, four of the 14 children with definite envenomation returned negative results of Venom Detection Kit tests. This is in accord with the results in adults, where about half of the envenomed patients returned negative results.⁴
A positive result of a Venom Detection Kit test, unless accompanied by clinical or laboratory evidence of envenomation, is not an indication for antivenom use. A positive test may be a false positive or represent subclinical envenomation. In our study, venom was detected in the urine of a number of children but tests of blood or bite swabs were negative. These children remained quite well without treatment.

Antivenom is not indicated unless clinical features or laboratory investigations suggest systemic envenomation.

Once envenomation is diagnosed the Venom Detection Kit provides a rapid guide to the snake genus and is used to guide antivenom therapy so that monovalent (instead of polyvalent) antivenom can be used where possible.
Detection of venom at the bite site also allows anticipation of genus-specific effects (such as rhabdomyolysis with tiger snake envenomation).
Some inaccuracy in the type of venom detected has been found. The Perth study in adults noted two cases where the Venom Detection Kit indicated different venom types in sequential tests on the same patient.⁴ The potential for an erroneous result is greatest when a blood sample is used.⁸

New CSL Venom Detection Kits

The new CSL Venom Detection Kit, a rapid simultaneous sandwich enzyme immunoassay (which tests for more than one venom simultaneously), has been available since July 1991. Laboratory studies⁹ have shown that it is able to detect venom at a concentration as low as 10 ng/mL in sample diluent. At high concentrations of venom, the kit may be positive for more than one type of venom, with a reduced specific venom reaction (a phenomenon known as the "high dose hook effect"). The correct result can be obtained by retesting a diluted sample.

The clinical performance of the Venom Detection Kit needs to be assessed by a prospective study of all patients presenting with possible and definite snakebite.

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