Detection of lupus coagulant

There is no direct test for the lupus anticoagulant (LA). Detection is based upon its inhibitory actions on coagulation. It binds to phospholipid on the platelet surface and interferes with the formation of the prothrombin activator complex.

The classical findings for a LA assay include:

• prolongation of a phospholipid-dependent clotting test.
• demonstration of the presence of an inhibitor by mixing tests.
• demonstration of the phospholipid dependence of the inhibitor.

Screening tests for LA include:

• activated partial thromboplastin time (APTT)
• dilute Russell's viper venom time (DRVVT)
• kaolin clotting time (KCT)

Confirmatory tests of the presence LA include:

• mixing tests with normal plasma
• confirmation of phospholipid dependence - the platelet neutralization procedure (PNP) is commonly used.
  • platelet neutralization procedures
    • LA-insensitive reagents
    • high-concentration phospholipid

The 2012 edition of BCSH guidelines recommends that

• DRVVT and one other test should be employed for LA detection (2C), and the patient regarded as having a LA if either test is positive
• a confirmatory step (e.g. using a high phospholipid concentration, platelet neutralizing reagent or LA-insensitive reagent) is needed to demonstrate phospholipid dependence (1)

Note:

• is not recommended in patients receiving vitamin K antagonists (VKA) because exclusion of a LA is problematic whilst the international normalized ratio (INR) is in the therapeutic range (1)

Reference:

• (1) Keeling D et al.Guidelines on the investigation and management of antiphospholipid syndrome. Br J Haematol. 2012;157(1):47-58.