* A diagnosis of hereditary protein S deficiency cannot be made in the presence of one of these disorders. If repeat testing is not possible due to persistence of a condition that can account for low protein S levels, other approaches to testing (eg, testing family members) may be discussed with the consulting hematologist. ¶ In patients receiving warfarin, measure free protein S antigen level after cessation of warfarin anticoagulation for at least 2 weeks. For individuals who cannot discontinue their vitamin K antagonist and whose management would be altered by the results of protein S testing, the consulting hematologist may substitute a different anticoagulant (eg, heparin, a direct oral anticoagulant) for 2 weeks and repeat the testing. Δ In patients taking estrogen-progestin contraceptives, measure free protein S antigen level after the patient has not received estrogen for at least 1 to 2 months.
