The 20 Minute Whole Blood Clotting Test (WBCT) is a simple, rapid test used in resource-limited settings, particularly to evaluate clotting in patients suspected of envenomation by snakebites, especially those causing coagulopathy.
Here’s a step-by-step whole blood clotting test procedure :
- Clean the venipuncture site with an alcohol swab and allow it to air dry.
- Using a sterile needle and syringe, draw 2-3 mL of venous blood.
- Quickly transfer the collected blood into the clean, dry glass test tube
- Ensure the test tube is completely free of anticoagulants or moisture, as these can interfere with clotting.
- Place the test tube in a secure position at ambient room temperature.
- Do not disturb the test tube during the observation period.
- After 20 minutes, gently tilt the tube to assess the presence of a clot.
Result interpretation
- Normal clotting function. If the blood has clotted, the patient likely does not have significant coagulopathy.
- No clot. This indicates that the blood is not clotting properly, which is common in viper envenomation or disseminated intravascular coagulation (DIC).
Purpose of whole blood clotting test
- To detect coagulopathy caused by snake venom, particularly in viper or other snakebite cases.
- Often used in rural or emergency settings where laboratory facilities are not available.
Equipment and Materials
- A clean, dry glass test tube (10 mL capacity; no anticoagulants).
- A stopwatch or timer.
- Disposable syringe or lancet for blood collection.
- Alcohol swab for skin preparation.
- Gloves and personal protective equipment (PPE).
Precautions during whole blood clotting test
- Use only clean, dry glass tubes; moisture or anticoagulant residues will invalidate the test.
- Avoid shaking or disturbing the test tube during the observation period.
- Perform the test at room temperature (20-25°C); temperature extremes can alter clotting times.
Clinical Significance whole blood clotting test
- A failure to clot within 20 minutes is a strong indicator of coagulopathy, often seen in cases of:
- Viperidae snake envenomation (e.g., Russell’s viper, saw-scaled viper).
- Severe coagulopathies such as DIC or liver failure.
- Immediate intervention, such as antivenom administration or transfusion of clotting factors, may be required.
Limitations of whole blood clotting test
- This is a crude test and does not quantify the degree of clotting factor deficiency.
- It may not detect mild clotting abnormalities.
- Laboratory-based tests (e.g., PT, aPTT, INR, fibrinogen levels) are needed for detailed evaluation.