The frequency of lupus anticoagulant in systemic lupus erythematosus. A study of sixty consecutive patients by activated partial thromboplastin time, Russell viper venom and anticardiolipin antibody level - Petri, M; Rheinschmidt, M; Whiting-O'Keefe, Q; Hellman, D; Corash, L (Ann Intern Med, 1987)