DRVVT Interpretation Guide for Lupus Anticoagulant

Dr Abdul Mannan FRCPath FCPS

Blood 🩸Doctor

What is DRVVT?

The Dilute Russell Viper Venom Time (DRVVT) test is a functional clotting assay used to detect Lupus Anticoagulant (LA). It works by adding Russell Viper Venom, which directly activates Factor X to Xa, bypassing factors VIII and IX in the coagulation cascade. This makes it particularly sensitive to inhibitors that interfere with phospholipid-dependent clotting reactions, such as Lupus Anticoagulant.

The Three-Step DRVVT Process

Screen test (low phospholipid concentration): Prolonged if LA is present or if there's a factor deficiency.
Mix test (patient plasma + normal pooled plasma): Helps distinguish between factor deficiency and inhibitor presence.
Confirm test (high phospholipid concentration): The addition of excess phospholipid should correct LA-induced prolongation, as it neutralises the antibody.

Results are typically expressed as ratios (patient clotting time / normal control clotting time). A cut-off ratio of >1.2 is generally considered abnormal, though this may vary between laboratories.

Enhanced DRVVT Interpretation Table

DRVVT Screen	1:1 Mix	DRVVT Confirm	Screen/Confirm Ratio	Interpretation	Clinical Action
≤1.20	—	—	—	Normal Result	No LA detected. Consider alternative tests if clinical suspicion remains high
>1.20	<1.20	—	—	Factor Deficiency	Check factors II, V, X. Consider vitamin K deficiency or warfarin effect
>1.20	>1.20	<1.20	≥1.20	Lupus Anticoagulant Present	Confirm with second method (aPTT-based). Repeat in 12 weeks if APS suspected
>1.20	>1.20	>1.20	<1.20	Non-phospholipid Inhibitor	Screen for heparin/DOACs. Consider specific factor inhibitors if negative

Clinical Considerations

When interpreting DRVVT results, it's important to consider:

Anticoagulant therapy can interfere with results (heparin, DOACs, warfarin)
LA testing should be performed before starting anticoagulation when possible
Per ISTH guidelines, LA diagnosis requires at least two positive phospholipid-dependent tests
Results should be interpreted in the clinical context (thrombosis history, autoimmune disease)

Simplified Mnemonic for Remembering Patterns

To remember the interpretation patterns:

Mix corrects → think deficiency (deficiencies are "fixed" by adding normal plasma)