20 minute whole blood clotting test (20 WBCT):

– It is a bedside test.

– Place 2 ml of freshly sampled venous blood in a small glass test tube and leave undisturbed for 20 minutes at ambient temperature.

– Gently tilt the test tube to see if the blood is still liquid; the patient has hypofibrinogenaemia

(“incoagulable” blood or “not clotted”) as a result of venom-induced consumption coagulopathy (Figure 7).

– If blood clot is formed and signs and symptoms of neurotoxic envenomation present, classify as neurotoxic envenomation.

– If there is any doubt, repeat the test in duplicate, including a “control” (blood from a healthy person).

Caution: If the test tube used for the test is not made of ordinary glass, or if it has been used before and cleaned with detergent, its wall may not stimulate clotting of the blood sample in the usual way and test will be invalid).

Counsel patient and relatives in the beginning that, 20WBCT may be repeated several times before giving any medication.


– If clotted, the test should be carried out every 1 h from admission for three hours and then 6 hourly for 24 hours. In case test is non-clotting, repeat 6 hour after administration of loading dose of ASV. In case of neurotoxic envenomation repeat clotting test after 6 hours.

Other investigations that may assist in the management of snake bite at various levels of healthcare