The Whole Blood Clotting Test (WBCt), often referred to as the Whole Blood Clotting Time (WBCT), is a straightforward bedside test used to evaluate the intrinsic pathway of the coagulation cascade.
How to Perform a Whole Blood Clotting Test (WBCt/WBCT)
Performing a Whole Blood Clotting Test involves careful sample collection and precise timing to assess the blood's ability to clot. Here’s a detailed guide to the procedure:
1. Materials and Preparation
Before starting the test, ensure you have all the necessary materials ready. The choice of equipment is crucial for accurate results.
- Test Tube: A 10-mL glass test tube is well-suited for this test. Glass tubes promote clotting, making them ideal for this assessment.
- Syringe/Collection Device: For drawing blood.
- Timer: A reliable timer is essential for accurate assessment intervals.
2. Sample Collection
The method of blood collection directly impacts the reliability of the test results, especially to avoid dilution or premature activation of clotting.
- Standard Venipuncture:
- Collect a sufficient volume of whole blood directly into the test tube.
- Ensure a clean venipuncture to minimize tissue factor contamination, which could falsely shorten the clotting time.
- Collection from Existing Intravenous (IV) Catheters:
- When collecting a sample from an existing IV catheter, it is critical to perform a 2 mL waste draw first. This step ensures that the collected sample is undiluted by any IV fluids or heparin that might be present in the catheter line, which could interfere with the clotting process.
- After the waste draw, collect 2 mL of undiluted whole blood into the 10-mL glass test tube. It's important to measure this volume precisely.
3. Incubation and Assessment
Once the blood sample is collected, the test tube should remain undisturbed initially, and then assessed at specific intervals.
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Initial Incubation: After placing the blood into the tube, avoid shaking or agitating the tube immediately. Start your timer as soon as the blood enters the test tube.
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Assessment Intervals: The clotting process is assessed at two precise time points:
- 20 minutes: Gently tilt the tube to observe if a clot has formed.
- 30 minutes: Re-assess the tube. A clot should ideally be visible by this time.
Precision is key: Assess at 20 and 30 min precisely to ensure consistent and comparable results. The presence or absence of a clot at these specific times provides valuable information regarding the patient's coagulation status.
Key Considerations for Accurate WBCt
| Aspect | Detail | Importance |
|---|---|---|
| Test Tube Type | 10-mL glass test tube | Glass surfaces activate the intrinsic coagulation pathway, which is essential for the test. |
| Sample Volume | 2 mL of whole blood per tube | Ensures appropriate blood-to-surface area ratio for consistent clotting. |
| IV Catheter Draw | Perform a 2 mL waste draw before collecting the sample. | Prevents sample dilution by IV fluids or heparin, ensuring an undiluted sample. |
| Assessment Times | Precisely at 20 and 30 minutes post-collection. | Standardized timing is crucial for interpreting results accurately. |
| Sample Agitation | Avoid vigorous shaking or agitation of the tube immediately after collection and during assessment, as this can affect clotting time. Gently tilt to observe. | Prevents premature or inhibited clot formation. |
By following these precise steps, you can accurately perform a Whole Blood Clotting Test to evaluate a patient's coagulation profile.
