Here is an excellent patient's guide to managing your INR levels with warfarin(coumadin)
http://pfrc.med.nyu.edu/handouts/pdf/medic/warfa.pdf
As you'll see the most important thing is consistency in your diet, particularly with green leafy veg intake. The INR values will change fairly quickly with changes in diet ... nearly day by day, unlike cholesterol which tends to be about every two weeks, or blood sugar which is almost by the quarter hour!
An unusually heavy "green" mean the day before an INR test will produce an unusual result compared to a day without.
