Use of the Snake Venom Detection Kit

Use of the Snake Venom Detection Kit is the soundest method of discovering the immunotype to which the snake responsible for the envenomation belongs. This is the important information to have when choosing antivenom. Determination of species may be aided by considering the snakes geographical distribution. Further confirmation may be made by considering specific symptoms.

Kit Components
Sample Selection
Sample Preparation
Recommended Method
Interpretation of Results
Notes

KIT COMPONENTS

SAMPLE SELECTION

Test specimen options include:

The SVDK is capable of detecting and immunotyping venom from any tissue, body fluid or other biological sample. The best type of sample to use is dependent on the patient presentation, the case history and the available samples for each case. Generally, a bite site swab will provide the most valuable result followed by urine and then whole blood. If the bite site is dry, a valuable sample may be obtained from affected potions of clothing or bandages. Although blood may be used and often gives a valuable result, interference may occur from free haemoglobin or rheumatoid factor and this can result in an invalid test. For this reason, bite site swabs or urine are more reliable.

SAMPLE PREPARATION

1. Prepare the Test Sample.

Note: There is enough yellow sample diluent in one vial to perform two snake venom detection tests. This will allow repeat testing of the original sample should there be a processing failure during the initial test.

Bite Site Swab:

Affected Bandage or Cloth Specimen:

Urine Specimen:

Plasma or Blood Specimen: Plasma or serum is the preferred blood based sample, however, whole anticoagulated blood is recommended in urgent situations as this sample does not require centrifugation and is therefore available more rapidly. A plasma or whole blood sample should be used if a bite site or urine specimen is not available.

Note: Erroneous reactions resulting in an invalid assay may occur if a whole blood specimen is tested.

Other Samples:

RECOMMENDED METHOD

2. Preparing the Test Strip.

3. Adding the Test Sample.

4. Removing the Well Contents.

5. Washing the Test Strip.

Note: Insufficient washing during this step may cause erroneous results.

6. Adding the Chromogen Solution

7. Adding the Peroxide Solution

8. Reading Colour Reactions

INTERPRETATION OF RESULTS

Test Validation The SVDK has an in-built positive and negative control to ensure that each test gives a valid result. For the test to be valid the negative control (well 6) should be visually clear, with no blue colour. The positive control (well 7) should show rapid blue colour. This indicates that all SVDK components are active and performing correctly.

Test Interpretation Australian snake venoms are immunologically cross-reactive, therefore, the first well (wells 1-5) to show colour development (with the exception of the positive control) should be taken as diagnostic. Please note that other wells may change colour but at a much lower rate. Very high levels of venom in a sample may cause rapid and confusing colour development. If two or more wells show similar rates of colour development, the sample should be further diluted and retested. This can be achieved by adding 1 drop of the diluted specimen to an unused yellow sample diluent vial (approximately a 1:30 dilution) and retested using the test method above. Positive reactions in wells 1-5 indicate the presence of venom and define the snake’s immunotype and the appropriate monovalent antivenom for treatment. Remember, a positive result does not always mean that clinical envenomation has occurred. A positive result is only an indication of the venom immunotype and the type of antivenom to be given if the patient requires antivenom therapy based on clinical or laboratory test result evidence.

Notes:
1. Positive findings of venom at the bite site, in the absence of systemic symptoms, is not an indication for the use of antivenom, as venom may not have entered the circulation. Similarly, a positive venom detection in urine is not, alone, a reason for commencing antivenom therapy. Conversely, a negative SVDK result in a patient with systemic symptoms is not a reason for withholding antivenom. Venom may not be present in the sample used or the venom may be from an unusual venom immunotype.

2. A positive SVDK result does not mean the patient has clinically significant envenomation. The SVDK can detect venom in concentrations as low as 0.01ng/mL and at levels below that which can cause clinical envenomation. A positive SVDK result is therefore not an indication to give antivenom. It is an indication of the type of monovalent antivenom to give if the clinical decision is made to use antivenom therapy based on clinical symptoms and laboratory test results.

3. Snake venom in an envenomated patient will be neutralised and undetectable after adequate amounts of the appropriate antivenom is administered. This effect should be recognised if SVDK samples are collected and tested after the administration of antivenom. Venom will immediately become undetectable in blood and serum samples collected after sufficient antivenom is administered. Venom will also cease to be excreted in urine collected after sufficient antivenom is administered. This means that it is likely that urine samples will become negative, depending on the patient’s urine output and next urine voiding event.

 

 

 

 

 

 

Last updated: December 2006
Text supplied by CSL Limited.