20WBCT interpretation — DTM&H MCQ

Correct answer: C — Consumption coagulopathy confirming systemic envenomation

The correct answer is C, consumption coagulopathy confirming systemic envenomation. Failure of blood to clot in a clean, dry glass tube after 20 minutes reflects venom-induced consumption of clotting factors (particularly fibrinogen), a hallmark of venom-induced consumptive coagulopathy (VICC) following envenoming by species such as vipers. The 20WBCT is the WHO-recommended bedside surrogate for laboratory clotting studies in resource-limited settings, used specifically to decide whether antivenom is indicated. A positive test (non-clotting) is a validated, low-cost, high-sensitivity indicator of systemic envenoming and directly triggers antivenom therapy, since coagulopathy signifies venom has entered the circulation rather than remaining a purely local bite reaction. Why the other options are wrong: E. Incorrectly collected: the test protocol mandates a new, clean, dry glass tube free of detergent residue precisely to avoid false positives from contamination; a properly performed test failing to clot is a true result, not a technical error. A. Anticoagulant medication use: while anticoagulants can prolong clotting, this is not the expected or intended interpretation in the context of a snakebite victim being assessed for envenoming, and clinical practice attributes a positive 20WBCT to venom effect unless a clear anticoagulant history exists. B. Normal result in a haemophilia patient: haemophilia is not remotely relevant to snakebite triage and this option deliberately misattributes a coagulation defect to an unrelated congenital disorder rather than the acute venom effect being tested for. D. Non-venomous bite with vasovagal response: vasovagal reactions cause haemodynamic symptoms, not defibrination or factor consumption, and have no bearing on in vitro clot formation. Key point: A non-clotting 20WBCT at 20 minutes confirms venom-induced consumption coagulopathy and systemic envenoming, mandating antivenom administration.

Reference: WHO Guidelines for the Prevention and Clinical Management of Snakebite in Africa/Guidelines for the management of snakebites, 2nd edition (2016), Twenty Minute Whole Blood Clotting Test (20WBCT) section: https://apps.who.int/iris/handle/10665/249547