<prompt> A 45 year old lady with normal PT and increased aPTT. About 2 year back, she was operated for cholecystectomy did not have any bleeding episode.What is next investigation for clinical diagnosis ?Factor VIII assayDilute russel viper venom assayPlatelet aggregation testRistocetin cofactor assay  <response>: Answer- B. Dilute russel viper venom assayDilute Russel viper venom test is one of the test to detect lupus anticoagulant.Lupus anticoagulant is associated with prolongation in PTT and thrombosis no bleeding 