1. What is DRVVT Ratio?

The DRVVT (Dilute Russell's Viper Venom Time) ratio is calculated by dividing the patient's DRVVT by the normal control DRVVT. It's used as a screening test for lupus anticoagulant in the evaluation of antiphospholipid syndrome.

2. How Does the Calculator Work?

The calculator uses the DRVVT ratio formula:

Where:

• \( Patient\ DRVVT \) — Patient's dilute Russell's viper venom time in seconds
• \( Normal\ DRVVT \) — Normal control DRVVT in seconds

Explanation: The ratio compares the patient's clotting time to the normal control time, with higher ratios suggesting the possible presence of lupus anticoagulant.

3. Importance of DRVVT Ratio

Details: The DRVVT ratio is crucial for detecting lupus anticoagulant, which is associated with an increased risk of thrombosis and pregnancy complications in antiphospholipid syndrome.

4. Using the Calculator

Tips: Enter both patient DRVVT and normal control DRVVT in seconds. Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is a normal DRVVT ratio?
A: Typically, a ratio ≤1.2 is considered normal. Ratios >1.2 may suggest the presence of lupus anticoagulant.

Q2: When should DRVVT testing be performed?
A: When antiphospholipid syndrome is suspected, in cases of unexplained thrombosis, recurrent pregnancy loss, or prolonged PTT.

Q3: What factors can affect DRVVT results?
A: Heparin contamination, high hematocrit, and certain anticoagulants can affect results. Testing should be done when the patient is off warfarin if possible.

Q4: Is DRVVT ratio alone diagnostic?
A: No, diagnosis requires persistent positivity (12 weeks apart) along with clinical criteria. Additional testing like hexagonal phase phospholipid neutralization may be needed.

Q5: How does DRVVT differ from aPTT?
A: DRVVT is more specific for lupus anticoagulant as it bypasses the intrinsic pathway and is less affected by factor deficiencies than aPTT.