Antiphospholipid Antibody Test (e.g., dRVVT)

 


1. Objective:

To detect antiphospholipid antibodies in patient plasma, especially in suspected cases of antiphospholipid syndrome, using the Dilute Russell’s Viper Venom Time (dRVVT) test.

2. Principle:
The dRVVT measures the time it takes for plasma to clot after the addition of diluted Russell's viper venom, which directly activates factor X. In the presence of antiphospholipid antibodies, especially lupus anticoagulant, the clotting time is prolonged. A confirmatory test with excess phospholipids is used to demonstrate correction.

3. Materials Required:

  • Patient citrated plasma

  • Normal pooled plasma (control)

  • Russell’s viper venom reagent (screening and confirmatory)

  • Calcium chloride

  • Platelet-poor plasma

  • Coagulometer or water bath with stopwatch

  • Test tubes and pipettes

4. Procedure:

  1. Collected citrated blood and prepared platelet-poor plasma.

  2. Added venom reagent to both patient and control plasma.

  3. Added calcium chloride to initiate clotting.

  4. Measured clotting time (screen).

  5. Repeated test with confirmatory reagent containing excess phospholipid.

  6. Compared clotting times between screen and confirm.

5. Result:

  • Prolonged screen time with correction upon confirmatory test indicates presence of lupus anticoagulant (positive dRVVT).

  • No prolongation or no correction suggests absence of antiphospholipid antibodies or other coagulopathies.

6. Interpretation Table Example:

SampleScreening TimeConfirm TimeRatio (Screen/Confirm)Interpretation
Patient A52 sec35 sec1.49Positive (LA detected)
Normal Ctrl36 sec34 sec1.05Negative

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