Explanation: Although he does have low protein C and S activity levels, he was on warfarin at the time of testing. These are both vitamin K–dependent proteins and will be low when a patient is on warfarin. This will need to be rechecked when the patient is off of warfarin for at least a month. The effect of warfarin on protein S especially can last for up to 4 weeks. Although he does have elevated FVIII activity, the level is not >250% and it was obtained in the acute setting. This is more likely an acute phase reactant and a result of the DVT. It will also have to be rechecked prior to stopping anticoagulation. If FVIII remains elevated after 3–6 months, he has increased risk of post-thrombotic syndrome and recurrent DVT. Although obesity is a risk factor, the most important contributor is an orthopedic injury requiring immobilization of the leg.
Question 2
