Depends.. is this a new diagnosis or an ongoing history?
You're going to definitely need to look at the patient's baseline PT, PTT and INR because you know the person is most likely either currently taking or going to need coumadin. If it is a new diagnosis, the person will also probably be on a heparin drip, so PTT is especially important. The pt will also probably need CBC and lytes to check for possible other underlying causes (esp Na and K) and thyroid function tests to check for hyperthyroidism. Cardiac markers such as troponins or CK/CK-MB may also be drawn to check for cardiac damage.
If the pt has a history of a-fib, lab tests might include PT, PTT and INR for coumadin or digoxin levels.
Hopefully this answer isn't too late!