Snakebite, scorpion and envenomation

20WBCT and venom-induced coagulopathy

Reviewed Nov 2026·2 references
New· views rounded down, updated weekly

The 20-minute whole blood clotting test is the bedside decider for haemotoxic envenoming in India. Use a new clean dry glass tube, do it serially, and do not let a single normal result reassure you; ASV, not FFP, corrects VICC.

At the bedside

Timed steps
  1. 1

    Standard technique

    Method

    2 mL fresh venous blood into a NEW, CLEAN, DRY GLASS tube; leave undisturbed 20 min at room temperature; tilt once. Blood flows = incoagulable (positive).

  2. 2

    Know the limits

    Accuracy

    Pooled sensitivity ~84% and specificity ~91% for INR > 1.4; a clotted result does not exclude evolving coagulopathy.

  3. 3

    Repeat

    Schedule

    If clotted: hourly for 3 h, then 6-hourly for 24 h. If non-clotting: repeat 6 h after each ASV loading dose.

  4. 4

    Where available

    Labs

    PT/INR, fibrinogen, platelets, creatinine, CK, urine for blood/myoglobin; INR does not replace serial 20WBCT in resource-limited settings.

  5. 5

    ASV first

    Treat

    Clotting factors (FFP/cryo) only for life-threatening bleeding after ASV; they are consumed by circulating venom otherwise.

Red flag · call your senior now
Spontaneous systemic bleeding beyond 20 min from bite: give ASV without waiting for 20WBCT.
Red flag
Intracranial bleeding: altered sensorium or focal signs in a viper bite.
Pitfall
Using plastic tubes or reused vials – false 'non-clotting' results.
Pitfall
Shaking the tube or checking repeatedly before 20 min.
Pearl
Hump-nosed pit viper coagulopathy (Western Ghats) does not respond to Indian polyvalent ASV and can last up to 3 weeks.

References

  1. 1

    Lamb T, Abouyannis M, de Oliveira SS, et al. The 20-minute whole blood clotting test (20WBCT) for snakebite coagulopathy – a systematic review and meta-analysis of diagnostic test accuracy. PLoS Negl Trop Dis. 2021;15(8):e0009657

  2. 2

    Directorate General of Health Services, Ministry of Health and Family Welfare, Government of India. Standard Treatment Guidelines: Snakebite. New Delhi: MoHFW/NHSRC; June 2016

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