How long before Effexor XR will not show up on blood test?

I've been on Effexor XR 75 MG for about 3-4 years - I want off of it and have cut it down to 37.5 MG the last couple of days - it's going ok - I've been through it before - I look to stop taking it completely within a week or so. I want to know how long before it is out of my system (blood) and will no longer show up on a blood test. I know it stays in your brain for a bit - but how long before it's out of your blood completely? I'm tappering off of it this time - I went cold-turkey before - having to get back on it later because of anxiety. But I've heard its better to slower reduce dosage...its easier on your body. I've read about the half-life and all that - but need to get it totally out of my blood system. THANK YOU! =)