Hematology

20 minute whole blood clotting test procedure, precautions

The 20 Minute Whole Blood Clotting Test (WBCT) is a simple and rapid test. It is used in resource-limited settings. It is particularly useful for evaluating clotting in patients suspected of snakebite envenomation. This is especially relevant for snakebites 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.